Immunohistochemical localization of low density lipoprotein receptor-related protein 1 and alpha(2)-Macroglobulin in retinal and choroidal tissue of proliferative retinopathies

The immunolocalization of the low density lipoprotein receptor-related protein 1 (LRP1) and its ligand alpha 2-Macroglobulin (alpha(2)M) was examined in tissues from human donor eyes of normal, diabetic and sickle cell disease subjects. Streptavidin alkaline phosphatase immunohistochemistry was performed with a mouse anti-human LRP1 and rabbit anti-human alpha(2)M antibodies. Retinal and choroidal blood vessels were labeled with mouse anti-human CD34 antibody in adjacent tissue sections. Mean scores for immunostaining from the pathological and control eyes were statistically compared. LRP1 immunoreactivity was very weak to negative in the neural retina of normal subjects except in scattered astrocytes. LRP1 expression in diabetic eyes was detected in the internal limiting membrane (ILM), astrocytes, inner photoreceptor matrix, choriocapillaris and choroidal stroma. The ligand alpha(2)M, however, was limited mainly to blood vessel walls, some areas of the inner nuclear layer (INL), photoreceptors, RPE-Bruch's membrane-choriocapillaris complex, intercapillary septa, and choroidal stroma. In sickle cell eyes, avascular and vascular retina as well as choroidal neovascularization (CNV) were analyzed. In avascular areas, LRP1 immunoreactivity was in innermost retina (presumably ILM, astrocytes, and Muller cells) and INL as well as RPE-Bruch's membrane-choriocapillaris complex and choroidal stroma. alpha(2)M was very weak in avascular peripheral retina compared to vascularized areas and limited to stroma in choroid. In contrast, in areas with CNV, LRP1 immunoreactivity was significantly decreased in overlying retina and in RPE-Bruch's membrane and choroidal stroma compared to the controls, while alpha(2)M was elevated in RPE-Bruch's membrane near CNV compared to normal areas in sickle cell choroid. The mean scores revealed that LRP1 and alpha(2)M in neural retina were significantly elevated in astrocytes and ILM in diabetic eyes (p < or = 0.05), whereas in sickle cell eyes scores were elevated in ILM and INL (p < or = 0.05). In addition, alpha(2)M immunoreactivity was in photoreceptors in both ischemic retinopathies. In choroid, the patterns of LRP1 and alpha(2)M expression were different and not coincident. This is the first demonstration of the presence of LRP1 and alpha(2)M in human proliferative retinopathies. Elevated LRP1 expression in sickle cell neural retina and diabetic inner retina and choroid suggests that LRP1 plays an important role in ischemic neovascular diseases.

Development of the human choriocapillaris

Vasculogenesis and/or angiogenesis are thought to be the major mechanisms for new vessel formation during development. A third mechanism, haemo-vasculogenesis, has been described in which blood vessel and blood cells (haematopoiesis (expression of CD34(+)) and erythropoiesis (presence of epsilon chain of haemoglobin or Hb-epsilon(+))) differentiate from a common precursor, the haemangioblast. This review describes the mechanism(s) for development of human choroidal vascular from 6 until 22 weeks gestation (WG). Endothelial cell or EC (CD31, CD34, CD39, VEGFR-2) and angioblast (CD39, VEGFR-2) markers were present in choriocapillaris (CC) by 7 WG through 22 WG. From 6 to 8 WG, many erythroblasts (nucleated Hb-epsilon(+) RBCs) were observed in the CC layer. Erythroblasts (Hb-epsilon(+)) were also positive for CD34, CD31, and/or VEGFR-2. Proliferation of vascular cells (Ki67+), suggesting angiogenesis, was not observed until 12 WG. TEM analysis demonstrated that CC was structurally immature even at 11 WG: no basement membrane, absence of pericytes, and poorly formed lumens that were filled with filopodia. Contiguous fenestrations and significant PV-1 (protein in diaphragms of fenestrations) were not observed until 21-22 WG. Smooth muscle actin was prominent at 20 WG and the maturation of pericytes was confirmed by TEM. Therefore, the embryonic CC appears to form initially by haemo-vasculogenesis (Hb-epsilon(+)/CD31(+) cells), whereas angiogenesis (CD34(+)/Ki67(+)) appears to be the mode of intermediate and large choroidal vessel development later in the foetus. Contiguous fenestrations, mature pericytes, and EC basal lamina occur late in development, around 22 WG, which coincides with photoreceptors developing inner segments.

Localisation of SDF-1 and its receptor CXCR4 in retina and choroid of aged human eyes and in eyes with age related macular degeneration

AIM

To examine the immunolocalisation of stromal cell derived factor 1 (SDF-1) and its receptor CXCR4 in aged control human donor eyes and eyes with age related macular degeneration (AMD).

METHODS

Postmortem eyes from eight aged control donors (mean age 79.8 years) and from 12 donors with AMD (mean age 83.9 years) were cryopreserved and sectioned through the macular region. SDF-1 and CXCR4 were localised using streptavidin alkaline phosphatase immunohistochemistry and then sections were bleached. Three independent masked observers scored the immunohistochemical reaction product.

RESULTS

In aged control retinas, SDF-1 immunoreactivity was most intense in inner photoreceptor matrix (IPM). CXCR4 showed a similar pattern of immunostaining, but was more prominent in inner segments of photoreceptors. In aged control and AMD choroid, SDF-1 and CXCR4 localisations were most prominent in retinal pigment epithelial (RPE) cells and choroidal stroma. However, the intensity for SDF-1 was significantly reduced in RPE (p < 0.0001) and choroidal stroma (p < 0.05) in late AMD eyes. SDF-1 and CXCR4 immunoreactivities were weak or nearly absent in disciform scars with choroidal neovascularisation (CNV). Circulating cells, presumably leucocytes, were most intensely positive for CXCR4.

CONCLUSIONS

These results show that changes in distribution and relative levels of SDF-1/CXCR4 were not evident in early AMD. This suggests that SDF-1/CXCR4 may not contribute to the formation of CNV in AMD, in that CXCR4+ cells were not incorporated into neovascularisation. However, the examples of CNV studied were within disciform scars, so the authors cannot comment on the role of SDF-1/CXCR4 in the early stages of CNV formation.

Impaired expression of thrombospondin-1 in eyes with age related macular degeneration

AIMS

This study investigated the expression and localisation of thrombospondin-1 (TSP-1), a known anti-angiogenic extracellular matrix protein, in normal aged control human eyes and eyes with age related macular degeneration (AMD).

METHODS

Immunohistochemical analysis with mouse anti-human TSP-1 antibody and mouse anti-human CD 34 antibody, as a blood vessel marker, was performed on frozen sections from macular and peripheral blocks of aged control donor eyes (n = 12; mean age 78.8 years), and eyes with AMD (n = 12; mean age 83.9 years). Pigment in retinal pigment epithelium (RPE) and choroidal melanocytes was bleached. Three independent observers scored the immunohistochemical reaction product.

RESULTS

In the macular region, TSP-1 expression was observed intensely in Bruch's membrane and weakly in RPE basement membrane, choriocapillaris, and the wall of large choroidal blood vessels in the aged control eyes. In eyes with AMD, TSP-1 immunoreactivity was significantly lower in all structures except RPE basement membrane (p<0.01). There was significantly lower TSP-1 in the far periphery than the equator and submacular regions in all eyes. TSP-1 immunoreactivity was low in choroidal neovascularisation (CNV), but it was high and diffuse in adjacent scar tissue.

CONCLUSION

These findings suggest that decreased TSP-1 in Bruch's membrane and choroidal vessels during AMD may permit the formation of CNV.

Ocular structure and function in an aged monkey with spontaneous diabetes mellitus

Diabetes mellitus develops spontaneously in middle-aged, obese rhesus monkeys, thus making them a good model for examining the effects of co-morbid factors on the development of end-organ damage. Changes in structure and function in the eyes of one monkey who spontaneously developed type 2 diabetes are reported here. This animal had concomitant hypertension, high levels of triglycerides and serum cholesterol, and a low fraction of high-density lipoprotein. The eyes showed intraretinal hemorrhages and large areas of retinal capillary nonperfusion. Indo-cyanin green (ICG) angiography revealed a large area of non- or poorly perfused choriocapillaris in one eye, and immunohistochemistry showed loss of viable choriocapillaries in this region. Both basal laminar deposits and hard drusen were present on areas of Bruch's membrane adjacent to nonviable choriocapillaris. Blood flow via the nasal posterior ciliary arteries to this section of choroid was not detectable by color duplex Doppler ultrasound, indicating contribution of extraocular vascular disease to ischemia in this eye. There was a severe decline in number of photoreceptor inner and outer segments, and corresponding reductions in the multifocal electroretinogram (ERG), in the areas of choriocapillaris loss. The ganzfeld ERG indicated loss in both inner and outer retinal function. Much of the ganglion cell layer was absent throughout the retina, possibly reflecting the effect of diabetes as well as chronic open angle glaucoma; the latter diagnosis supported by elevated intraocular pressures and excavated optic disks. In summary, high resolution, enzyme histochemical and histopathological analyses of a diabetic hypertensive monkey retina and choroid after serial functional in vivo analyses have demonstrated the relationship between vascular dysfunction and visual function loss. Choroidal vascular dysfunction in both large and small vessels was associated with age-related macular degeneration-like changes in Bruch's membrane and photoreceptor degeneration.

Neutrophils and leucocyte adhesion molecules in sickle cell retinopathy

AIMS

The expression of the adhesion molecules ICAM-1, VCAM-1, and P-selectin, and the distribution and number of polymorphonuclear leucocytes (PMNs) were investigated in sickle cell retinopathy (SCR) and compared to the normal retina.

METHODS

Postmortem ocular tissue was obtained from five subjects (16, 21, 28, 40, and 41 years of age) with sickle haemoglobinopathies and from one control subject. Tissue was cryopreserved, and streptavidin peroxidase immunohistochemistry was performed with antibodies against ICAM-1, VCAM-1, and P-selectin. Immunohistochemical reaction product was scored, and PMN numbers were counted in sections stained with non-specific esterase.

RESULTS

Increased ICAM-1, VCAM-1, and P-selectin immunoreactivities were observed in sickle cell subjects compared to the control subject. The highest ICAM and P-selectin immunoreactivity was associated with intraretinal vessels adjacent to the preretinal neovascular formation in subjects with proliferative retinopathy. This was not the case with VCAM-1 immunoreactivity, which was highest in intraretinal vessels adjacent to the sea fan when the sea fan was still "in statu nascendi." Fully formed, "older" sea fans had the highest levels of VCAM-1. The increase in adhesion molecule immunoreactivity was paralleled by an increase in intraretinal PMNs. The number of intraretinal PMNs increased with progression of the disease and the numbers surpassed those in control subjects by threefold. In the sea fan with the greatest VCAM-1 immunoreactivity, there were 20 times more PMNs were observed than in the rest of the retina in the same subject.

CONCLUSION

These data suggest that adhesion molecule mediated leucocyte adhesion might play an important part in the vaso-occlusive phase of sickle cell retinopathy and in autoinfarction of sea fan formations.

Inhibition of TNF-alpha-induced sickle RBC retention in retina by a VLA-4 antagonist

PURPOSE

Patients with sickle cell disease have elevated circulating levels of cytokines including tumor necrosis factor (TNF) alpha. TNF-alpha stimulates expression by endothelial cells of adhesion molecules, including vascular cell adhesion molecule (VCAM) 1. Others have demonstrated that VLA-4 (alpha(4)beta(1)), a ligand for VCAM-1 or fibronectin, is present on a fraction of sickle reticulocytes. The intent of this study was to determine, using a rat model, if TNF-alpha increases retention of sickle erythrocytes in retina and if that retention can be inhibited.

METHODS

TNF-alpha was given intraperitoneally to rats 5 hours before IV administration of FITC-labeled, density-separated sickle erythrocytes. After 5 minutes, rats were exsanguinated, and retinas were excised and incubated for ADPase activity, permitting the determination of the number and location of retained cells.

RESULTS

TNF-alpha caused a three- to fourfold increase in retention of sickle erythrocytes in retinal capillaries (P < 0.05) but not of normal human erythrocytes. Preincubation of sickle erythrocytes with TBC772, a peptide that blocks the binding of alpha(4)beta(1) and alpha(4)beta(7), or a monoclonal antibody against VLA-4 (19H8), significantly inhibited the TNF-alpha-induced retention (P < or = 0.02), whereas a control cyclic peptide and antibody had no effect. IV TBC772 also inhibited sickle erythrocyte retention (P = 0.01). Two intravenously administered anti-fibronectin antibodies inhibited sickle cell retention as well, but an anti-rat VCAM-1 antibody did not inhibit retention.

CONCLUSIONS

The authors conclude that TNF-alpha stimulates retention of sickle erythrocytes in the retinal vasculature. This increased retention can be blocked by a VLA-4 antagonist, suggesting that the cells retained after cytokine stimulation are reticulocytes. The counter-receptor for VLA-4 in this rat retina model appears to be fibronectin and not VCAM-1, based on data obtained using antibodies against these molecules.

EMAP cytokine expression in developing retinas of normal and retinal degeneration (rd) mutant mice

Endothelial-monocyte-activating polypeptide (EMAP) is a proinflammatory cytokine and a mediator of programmed endothelial cell death. To gain insight into its possible functions during retinal development and degeneration, the cellular distribution of EMAP protein was compared in control and retinal degeneration (rd) mice. EMAP immunoreactivity was confined to the ganglion cell layer (GCL) and the inner nuclear layer (INL). There were significant differences in the intensity of EMAP labeling in the GCL and the INL when comparing control and rd mouse retinas. Rd retinas contain much more EMAP immunoreactivity in the GCL and the INL than the control retinas at postnatal day 14, which is the time point immediately after the onset of the degeneration of the rd retina. Histopathologic examination showed no significant abnormalities in the GCL and INL in the rd mouse, despite a great degree of photoreceptor cell death from P12 to P18. Light and electron microscopic studies immunolocalize EMAP protein to the cytoplasm of retinal ganglion cells, amacrine cells, and horizontal cells. The data suggests that EMAP is synthesized and accumulated as an intracellular precursor protein that has a functional role in translation and protein synthesis as a cofactor for tRNA synthetase. The increased expression of EMAP precursor levels in rd mouse retina may reflect the enhanced rate of translation and protein synthesis in the production of endogenous factors that promote survival in the GCL and INL.

Velocity measurements of normal and sickle red blood cells in the rat retinal and choroidal vasculatures

The purpose of this study was to develop an in vivo, noninvasive method to assess the velocities of normal and sickle red blood cells (RBCs) in the retinal and choroidal vasculatures of rats. Human and rat RBCs were isolated from whole blood, labeled with fluorescein isothiocyanate (FITC), and administered intravenously to anesthetized rats. A Rodenstock scanning laser ophthalmoscope (SLO) was used to image the FITC-labeled RBCs as an NTSC video signal. Video sequences of RBC transit in the retinal (pigmented rats) and choroidal (albino rats) vessels were captured directly to digital format. Following in vivo angiography, the animals were sacrificed, the eyes enucleated, and retinas prepared by our adenosine diphosphatase vascular labeling technique for viewing by conventional optical microscopy. Although rat and normal human RBCs differ slightly in size, their velocities were similar in the retinal arteries and capillaries (within 4%). Velocities of RBCs from sickle cell patients (sRBCs) were slower by 12 and 9% in arteries and by 38 and 25% in capillaries, compared to rat and normal human RBCs, respectively. Compared to velocities in retinal capillaries, the velocities in choroidal capillaries were much slower for rat RBCs (77%), normal human RBCs (79%), and sRBCs (67%). In contrast to normal human RBCs, sRBCs were often retained transiently in retinal capillaries at preferred sites, but in choroidal capillaries large numbers of cells were retained for extended periods. SLO imaging of FITC-labeled RBCs in rat retina and choroid provided a reliable method for evaluating normal and abnormal hemodynamics.

Localization of adenosine A2a receptor in retinal development and oxygen-induced retinopathy

PURPOSE

To investigate the association of adenosine A2a receptors (A2aR) with retinal vasculogenesis and angiogenesis that occurs in the canine model of oxygen-induced retinopathy (OIR).

METHODS

One-day-old dogs were exposed to 100/o oxygen for 4 days and killed in oxygen (5 days old) and at 3, 10, 17, and 23 days after exposure to hyperoxia. Room air control animals were killed at 1, 5, 8, 15, 22, and 28 days of age. Immunolocalization of A2aR was performed on frozen sections, and reaction product density was quantified using microdensitometry. Cell types were identified in serial sections using antibodies against von Willebrand factor (endothelial cells) and GFAP (astrocytes), and enzyme histochemistry for menadione-dependent a-glycerophosphate dehydrogenase (M-a-GPDH) (to label angioblasts and developing blood vessels).

RESULTS

A2aR immunoreactivity was associated with forming blood vessels and angioblasts in the nerve fiber layer (NFL) of peripheral retina. As development progressed, vascular labeling decreased, whereas labeling of neuronal elements increased. In OIR, A2aR immunoreactivity in the NFL was reduced after exposure to hyperoxia and significantly elevated in the inner retina throughout vascularized retina and in advance of forming vasculature in all oxygen-treated animals returned to room air. A2aR immunoreactivity was also prominent in fronds of intravitreal neovascularization.

CONCLUSIONS

A2aR immunoreactivity was associated with developing retinal vessels. As development progressed, vascular-associated A2aR labeling decreased and, concomitantly, labeling of neuronal elements increased. A2aR immunoreactivity was significantly elevated at the edge of forming vasculature in all animals returned to room air after hyperoxia and in intravitreal neovas cular formations. These results provide additional evidence for the importance of A2aR and its ligand adenosine in retinal vascular development and in the vasoproliferative stage of canine OIR.

5' nucleotidase and adenosine during retinal vasculogenesis and oxygen-induced retinopathy

PURPOSE

5' nucleotidase (5'N) is a major source of the vasogenic substance adenosine in most tissues. The distribution and relative levels of 5'N and adenosine were examined in neonatal dog inner retina during normal vasculogenesis and oxygen-induced retinopathy (OIR).

METHODS

Animals ranging in age from 1 to 22 days of age were used in this study. Adenosine immunolocalization was performed on frozen sections with an antibody against adenosine conjugated to laevulinic acid using a streptavidin peroxidase technique. Triplicate room air control animals at different postnatal ages and triplicate oxygen-treated animals at different time points during or after hyperoxic insult were analyzed. Adenosine immunoreactivity (AI) and 5'N enzyme histochemical reaction product were quantified using microdensitometry. Adjacent sections were incubated for von Willebrand factor to label blood vessels.

RESULTS

During normal vasculogenesis, AI was most prominent within the inner retina. The peak of immunoreactivity was located at the border of vascularized retina throughout the period of primary retinal vasculogenesis (1-15 days of age). At 22 days when vasculogenesis was complete, AI decreased within the inner retina. The highest 5'N activity was localized to inner Muller cell processes in inner retina and decreased after vasculogenesis was complete. In animals killed after 4 days of oxygen breathing, the vasoobliterative stage of OIR, AI and 5'N activity were reduced throughout the retina. During the vasoproliferative stage, AI was markedly elevated at the edge of reforming vasculature as well as throughout the more posterior inner retina where 5'N activity also was elevated. AI was also in intravitreal neovascularization.

CONCLUSIONS

Peak adenosine levels in the inner retina correlated temporally with active vasculogenesis. Adenosine and 5'N levels were reduced in hyperoxia and then returned to above normal levels during the vasoproliferative stage of OIR.

Angiogenic factors in human proliferative sickle cell retinopathy

BACKGROUND/AIMS

Preretinal neovascular formations called sea fans develop at the border of non-perfused peripheral retina in sickle cell retinopathy. Angiogenic factors which could contribute to their development, however, have not been examined previously. The objective of this study was to determine immunohistochemically if vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF) were associated with sea fan formations.

METHODS

Immunohistochemistry on cryosections was used to localise bFGF, VEGF, heparan sulphate proteoglycan, human serum albumin, collagens IV and II, and von Willebrand factor in tissue from five sickle cell and one control subject.

RESULTS

The greatest immunoreactivity for VEGF and bFGF was in the feeder and preretinal vessels of sea fans (p<0.01). The most prominent reaction product was localised to vascular endothelial cells. In retinal vessels, VEGF and bFGF immunoreactivities were greater in sickle cell subjects (both proliferative and non-proliferative) than in the control subject (p<0.01 and p<0.02 respectively). In the sickle cell retina, no angiogenic factor immunoreactivity was detected in non-perfused periphery and there was no significant difference in bFGF or VEGF immunoreactivity between perfused retina and the border of perfused and non-perfused areas.

CONCLUSION

Our results demonstrate for the first time that VEGF and bFGF are associated with sea fan formations in sickle cell retinopathy. Both factors may function in an autocrine manner because immunoreactivity for these factors was greater within the neovascularisation than in adjacent retina.

Senescence-associated beta-galactosidase histochemistry for the primate eye

PURPOSE

To develop a senescence-associated beta-galactosidase histochemistry and bleaching protocol for the primate posterior pole.

METHODS

Rhesus monkey eyes of different ages were enucleated after death, fixed in 4% paraformaldehyde for up to 16 hours, and cryoprotected using a graded sucrose infiltration technique. Ten-micrometer tissue sections were treated with beta-galactosidase, pH 4 (lysosomal) or pH 6 (senescence-associated) activity, for various times. Bleaching of retinal pigment epithelial (RPE) cell and choroidal melanocyte pigment was performed after beta-galactosidase histochemistry using 0.1% to 1% potassium permanganate incubation for 1 minute to 2 hours followed by 0.5% oxalic acid immersion.

RESULTS

A 6-hour incubation with beta-galactosidase, pH 4 or 6, demonstrated optimal staining of the RPE. Uniform staining of the RPE for pH 4 beta-galactosidase was seen in both young and old eyes. In contrast, senescence-associated beta-galactosidase (pH 6) staining was seen in the RPE of 16 and 29-year-old, but not 1- and 2-year-old eyes. Senescence-associated beta-galactosidase staining was evident in RPE cells adjacent to cuticular drusen. Optimal bleaching without loss of beta-galactosidase staining was obtained using a 25-minute incubation with 0.05% permanganate.

CONCLUSIONS

The senescence-associated beta-galactosidase histochemistry assay, adapted for use in the primate posterior pole, showed staining of RPE cells in older eyes. Visualization of beta-galactosidase activity in the RPE was enhanced by permanganate bleaching of melanin pigment. This technique could be valuable for identifying senescent RPE cells in human eyes.

Increase in the advanced glycation end product pentosidine in Bruch's membrane with age

PURPOSE

To determine whether there is an age-related increase of pentosidine in human Bruch's membranes and to localize pentosidine and carboxymethyllysine (CML), two well-characterized, advanced glycation end products (AGEs) in aged human Bruch's membranes and choroid in vivo.

METHODS

Human Bruch's membrane samples were isolated from the retinal pigment epithelium (RPE) and choroid and subjected to reversed-phase high-performance liquid chromatography to determine pentosidine content. A polyclonal anti-pentosidine antibody and a monoclonal antibody specific for carboxymethyllysine were used to localize AGEs in 20-month-old nondiabetic, 82-year-old nondiabetic, and 82-year-old diabetic globes.

RESULTS

Human Bruch's membranes (n = 20) showed a linear age-dependent increase in pentosidine that reached approximately 0.17 millimoles pentosidine per mole hydroxyproline in late life (r = 0.896; P < 0.001). Immunohistochemical evaluation showed evidence of pentosidine in Bruch's membrane, choroidal extracellular matrix, and vessel walls in the 82-year-old nondiabetic and diabetic globes. A similar staining pattern was found with the anti-CML antibody. Basal laminar deposits and drusen stained with both antibodies in the elderly nondiabetic eye. In contrast, neither antibody stained the 20-month-old tissue.

CONCLUSIONS

We provide biochemical and immunohistochemical evidence for the formation of pentosidine and CML structures in human Bruch's membrane and choroid with age. These changes could promote aging of the RPE-Bruch's membrane-choroid complex.

Clinical and histopathologic features of canine oxygen-induced proliferative retinopathy

PURPOSE

In previous studies the morphologic features of the acute vaso-obliterative and vasoproliferative stages of oxygen-induced retinopathy (OIR) were quantified and described in the dog model of retinopathy of prematurity (ROP). In the present study the sequelae of these events were examined using fluorescein angiography and histologic, enzyme, and immunohistochemical techniques.

METHODS

Thirty newborn animals were exposed to 95% to 100% oxygen for 4 days and returned to room air until they were 22 to 45 days of age. Before death some animals were anesthetized, and fluorescein angiography was performed. Retina and vitreous from some animals were processed for adenosine diphosphatase (ADPase) flat-embedding. In other cases, eyes were prepared for full-thickness eyewall sectioning or frozen for histochemical analysis.

RESULTS

Fluorescein angiography, funduscopic examination, and ADPase preparations showed dilated and tortuous retinal vessels, pigmentary changes, incomplete vascularization of peripheral retina, vitreous hemorrhage, and persistence of massive intravitreal neovascularization. Full-thickness eyewall sections showed tractional retinal folds, tented intravitreal vascularized membranes, and vitreous synchysis. Immunohistochemical analysis showed inner retinal astrogliosis. Enzyme histochemistry showed high alpha glycerophosphate dehydrogenase activity in poorly differentiated neovascular formations and low activity in formations with mature pericytes and endothelial cells.

CONCLUSIONS

End-stage OIR in the neonatal dog shares many features with the chronic human disease. These results provide additional support for the use of this model in experimental studies of ROP.

Retinal hypoxia in long-term diabetic cats

PURPOSE

To determine whether the retina is hypoxic in early stages of diabetic retinopathy in cats and to correlate intraretinal PO2 with fluorescein angiographic and histologic alterations.

METHODS

Intraretinal PO2 was measured with microelectrodes in three cats with long-standing diabetes (>6 years) that had been followed with fluorescein angiographs every 6 months. Average PO2 in the inner vascularized half of the retina was compared with similar measurements in 21 control animals. Photoreceptor oxygen consumption was also compared. The retinal vascular endothelium of the diabetic animals was stained for ADPase activity in flatmounts, and transverse sections were used to visualize microscopic alterations in vascular structure.

RESULTS

PO2 in the inner half of the retina was abnormally low in the diabetic cats, 7.7+/-5.2 mm Hg (35 penetrations in 3 cats) versus 16.4+/-9.3 mm Hg in normal cats (85 penetrations in 21 cats) (P << 0.001). Oxygenation was almost normal in some regions of the diabetic retinas, but little evidence of oxygen supply from the retinal circulation was observed in other regions. Inner retinal hypoxia was present in areas with no detectable capillary dropout in fluorescein angiograms or flatmounts. The worst changes histologically were microaneurysms, leukocyte and platelet plugging of aneurysms and venules, and degenerating endothelial cells in capillary walls. These histologic abnormalities were confined to small regions, some of which could be positively correlated with markedly abnormal PO2 profiles. Photoreceptor oxygen utilization was not affected in two diabetic cats, but was below normal in one animal in which choroidal PO2 was low.

CONCLUSIONS

This is the first direct demonstration of retinal hypoxia in early diabetic retinopathy, before capillary dropout was evident clinically. Hypoxia was correlated with endothelial cell death, leukocyte plugging of vessels, and microaneurysms.

Adenosine stimulates canine retinal microvascular endothelial cell migration and tube formation

PURPOSE

To evaluate the effects of adenosine and related substances on events that occur during vasculogenesis and angiogenesis, using in vitro assays.

METHODS

Adenosine (ADO), inosine (INO, an adenosine catabolite), and 5'-(N-ethylcarboxamido) adenosine (NECA, an adenosine agonist) were evaluated for their effect on the proliferation of canine retinal microvascular endothelial cells (DRME), using a cell count assay. Also, these substances and ADO receptor selective agonists and antagonists were evaluated in an assay for DRME chemokinesis by measuring random migration into a wound made in a confluent cellular monolayer. Finally, the effects of these substances on DRME cord formation were evaluated in a 3-dimensional collagen gel. Bovine retinal extract (RE) was used as a positive control for all assays.

RESULTS

There was no effect on proliferation of DRME by any of the substances related to adenosine, but VEGF yielded a 30% stimulation of proliferation. Retinal extract, 10 microM ADO and 1.2 nM VEGF stimulation of DRME migration was 2- to 2.5-fold greater than 10 microM INO yielded. In addition, a combination of 1.2 nM VEGF with 10 microM ADO exceeded the stimulation in migration by ADO only and VEGF only. The total length of tubes formed in the presence of 10 microM ADO was comparable to that formed in the presence of RE and was 11-fold greater than with 10 microM INO. Tube length with a combination of VEGF plus ADO was 36% greater than with retinal extract. Use of selective ADO receptor antagonists suggested that tube formation and the migration response may be mediated through both adenosine A1 and A2 receptors, but use of selective ADO agonists suggests that A2 receptors may be more important than A1 for endothelial cell migration.

CONCLUSIONS

This in vitro analysis suggests that adenosine may stimulate retinal vasculogenesis, an event which involves migration of angioblasts and their assembly into vascular cords, prior to canalization.

Choriocapillaris degeneration and related pathologic changes in human diabetic eyes

OBJECTIVES

To measure the extent of choriocapillaris degeneration (CCD) in diabetic choroids and to study the association of CCD with choroidal neovascularization and pathologic changes in Bruch's membrane-like basal laminar deposits.

MATERIALS AND METHODS

Human choroids from 10 postmortem subjects (diabetic, 5 [group 1]; nondiabetic, 5 [group 2]) were incubated for the histochemical demonstration of alkaline phosphatase and nonspecific esterase activities, permitting analysis of the choroidal vasculature and polymorphonuclear leukocytes, respectively. The tissue was then flat embedded and sectioned for structural analysis. Areas of CCD were measured in the flat perspective by computer-assisted image analysis and verified in cross-sections of flat-embedded tissue.

RESULTS

The CCD in choroids from subjects with diabetes (group 1) appeared in 2 patterns: diffuse (partial loss of alkaline phosphatase activity in a poorly defined area, ie, degeneration of some capillary segments) and focal (complete degeneration of choriocapillaris or loss of alkaline phosphatase activity in a relatively well-defined area). The mean+/-SD percentage of the choroid with focal CCD in group 1 was 5.08%+/-1.13% of the total choroidal area vs 1. 16%+/-0.35% in group 2 (P<.001). Focal CCD in group 1 was more prominent in the posterior pole than in the peripheral choroid. Choroidal neovascularization was associated with some areas of diffuse CCD in group 1. Pathologic changes in Bruch's membrane-like basal laminar deposits were often associated with CCD; the thickness of the deposits was greater in group 1 than in group 2 and greater in areas with focal CCD than in areas with diffuse or no CCD.

CONCLUSION

The percentage of choroid with focal CCD in group 1 choroids was more than 4-fold greater than that in nondiabetic choroids. The presence of CCD was related to basal laminar deposits and, in some cases, to choroidal neovascularization.

Nonperfusion of retina and choroid in transgenic mouse models of sickle cell disease

PURPOSE

To determine if vascular occlusion and nonperfusion is associated with the outer retinal atrophy, retinopathy, and choroidopathy (chorioretinopathy) that occurs in the alpha H beta S[beta MDD] and alpha H beta S [alpha MD beta MDD] transgenic mouse models of sickle cell disease.

METHODS

Mice from the alpha H beta S[beta MDD] and alpha H beta S[alpha MD beta MDD] transgenic mouse lines that express high levels of human beta S globin were anesthetized and administered horseradish peroxidase (HRP) intracardially. After 1 min, the animals were sacrificed, and the retina from one eye was excised, fixed, and developed in diaminobenzidine (DAB). The contralateral eye was fixed, embedded whole in glycol methacrylate, and HRP developed in 2.5 microns sections.

RESULTS

HRP reaction product (HRP-RP) and stained erythrocytes (RBCs) (due to endogenous peroxidase) were diffusely distributed within all vascular lumens in flatmount retinas from control animals (littermates homozygous for the mouse Beta Major deletion not expressing the beta S transgene). In 42.5% of the transgenic mice expressing beta S without any proliferative retinopathy, many blood vessels contained RBC plugs and lacked lumenal HRP-RP. In addition to packed RBCs, fibrin was sometimes present at sites of occlusion. In sections from whole eyes of the same animals, foci of photoreceptor degeneration were associated with areas of choriocapillaris nonperfusion (lumen that lacked HRP-PR). In areas with normal photoreceptors, the choriocapillaris appeared perfused (HRP-RP was present). In animals with proliferative chorioretinopathy, some neovascular formations lacked luminal HRP-RP, suggesting autoinfarction.

CONCLUSIONS

Nonperfused retinal and choroidal vessels were observed in mice from the alpha H beta S[beta MDD] and alpha H beta S[alpha MD beta MDD] lines without retinal and choroidal neovascularization, whereas, all mice with neovascularization had nonperfused areas. Furthermore, small foci of PR loss were associated with areas of nonperfused choriocapillaris. These results suggest that sickle cell-mediated vaso-occlusions are an initial event in the chorioretinopathy and outer retinal atrophy that occurs in these models.

T cell traffic and the inflammatory response in experimental autoimmune uveoretinitis

PURPOSE

To quantify S-antigen-specific (S-Ag) T cells in the retina after adoptive transfer, and to evaluate their role in the initiation and progress of destructive ocular inflammation in experimental autoimmune uveoretinitis (EAU).

METHODS

Lewis rats were administered 10 x 10(6) S-Ag-specific T cells from the SP35 cell line or 10 x 10(6) concanavalin A-stimulated syngeneic spleen cell lymphoblasts labeled with lipophilic PKH26 fluorescent dye immediately before intravenous inoculation. Labeled cells in each retina were counted at various times from 4 to 120 hours after cell transfer by fluorescence microscopic analysis of each dissociated retina. Recipient eyes were examined within the same period by light and confocal microscope.

RESULTS

SP35 T cells showed a biphasic distribution in the retina. The first peak of 160 cells/retina was noted at 24 hours. A steady decline of labeled cells at 48 and 72 hours was followed by a rapid increase at 96 and 120 hours. Concanavalin A-stimulated, control-labeled cell populations showed an identical peak at 24 hours but a persistent decline thereafter; only two or three T cells were present in each retina at 120 hours. Concurrent inoculation of SP35 cells and nonspecific T cell blasts did not produce more SP35 cells than control cells in the retina at any time. Microscopic analysis showed mononuclear cell infiltration of the iris, ciliary body, and aqueous humor at 48 hours, which intensified rapidly and persisted through 120 hours. Retinal inflammation did not begin until 80 hours. Mononuclear cell adherence to vascular endothelium and perivascular macrophage infiltration of the innermost layers progressed to edema, and profound destructive inflammation and loss of retinal stratification were observed at 120 hours.

CONCLUSIONS

There is no evidence of a blood-ocular or blood-retinal barrier to activated T cell blasts. Autologous S-Ag does not provoke a more rapid entry of specific T cells at that site. The data confirm that anterior segment inflammation precedes retinal inflammation, even though S-Ag-specific T cells were present in the retina within a few hours after cell transfer. Because S-Ag is clearly present in the retina, delay in antigen presentation at that site may account for the temporal difference between retinal and anterior segment inflammation.

Increased NADH oxidase activity in the retina of the BBZ/Wor diabetic rat

This morphological study demonstrates a role for endothelial cells in generating reactive oxygen species in early stages of retinopathy in the BBZ/Wor rat, an obese, noninsulin dependent model of diabetes. Hyperglycemia induced pseudohypoxia results in an imbalance in cytosolic NADH/NAD+. In the oxygen-rich environment of the retina, NADH oxidase generates superoxide radical which is dismutated to hydrogen peroxide. Localization of hydrogen peroxide by the cerium NADH oxidase enzyme activity cytochemical localization technique shows a statistically significant increase of peroxide localization in the central retina of diabetic rats as compared to age-matched, nondiabetic controls. Endothelial cell dysfunction, indicated by leakage of endogenous serum albumin, coincided with areas of NADH oxidase activity localization. In diabetic rats there are increased levels of fibronectin in areas of hydrogen peroxide localization. This in vivo, morphological study is the first demonstration of oxidative injury and endothelial cell dysfunction in the retina of a spontaneous, noninsulin dependent model of diabetes.

Vascular endothelial growth factor and vascular permeability changes in human diabetic retinopathy

PURPOSE

The authors used histochemical analysis to determine whether increased vascular endothelial growth factor (VEGF) immunoreactivity in diabetic retinal vessels is related to increased vascular permeability, as indicated by human serum albumin (HSA) immunostaining, or to presumed retinal hypoxia as demonstrated by decreased vascularity. A correlation between VEGF and HSA in cryosections with angiopathic changes in the adenosine diphosphatase (ADPase) flat-embedded fellow retinas was sought. Because VEGF is a heparin-binding protein, the relation between VEGF and heparan sulfate proteoglycan (HSPG) immunoreactivities was also investigated.

METHODS

Cryopreserved eyes from 18 diabetic and 9 nondiabetic subjects removed after death were sectioned and immunohistochemical analysis was performed with antibodies against VEGF, HSA, HSPG, vWf (von Willebrand factor), and collagen IV. The fellow retinas were prepared by our ADPase flat-embedding technique to determine the degree of diabetic retinopathy. The number of positive vessels for each antibody and antibody localizations were determined by light microscopy.

RESULTS

The average number of VEGF-stained vessels in diabetic retinas was significantly higher than in nondiabetic retinas (P = 0.04). In diabetic retinas, there was a positive correlation between the distribution of VEGF-positive vessels and the distribution of HSA- and HSPG-positive vessels. No such correlation was observed in nondiabetic eyes. In many cases, HSPG immunoreactivity appeared colocalized with VEGF immunoreactivity, suggesting VEGF binding to HSPG. The comparison with the ADPase flat-embedded fellow retinas suggested that increased VEGF immunoreactivity and vascular permeability may occur before morphologic changes in the vasculature.

CONCLUSIONS

Vascular endothelial growth factor immunoreactivity was correlated with increased vascular permeability to macromolecules and appears to be increased in diabetic subjects before the onset of retinopathy.

Histopathologic features of neovascularization in sickle cell retinopathy

PURPOSE

To examine the histopathologic and morphometric features of neovascular lesions in human proliferative sickle cell retinopathy.

METHODS

Postmortem ocular tissue was obtained from three subjects (aged 20, 28, and 40 years) with SS hemoglobinopathy and prepared for adenosine diphosphatase flat-embedding. Morphometric analysis was performed before serial sectioning.

RESULTS

Numerous active and autoinfarcted lesions were found that represented virtually all stages in the life cycle of preretinal neovascularization. These formations ranged from single small loops extending from arteries and veins along the retinal surface to the typical complex, elevated sea fan formations. Sea fans developed at hairpin loops and at arteriovenous crossings. There was an average of 5.6 connections between sea fans and retinal vessels; of these, 45% were arteriolar, 52.5% were venular, and 2.6% were at the capillary level. Six of eight sea fans were located at arteriovenous crossings. Autoinfarction appeared to occur initially within the sea fan capillaries. The average height of sea fans was 123 microns above the retinal surface.

CONCLUSIONS

Preretinal neovascularization in sickle cell retinopathy can arise from both the arterial and venous sides of the retinal vasculature and can assume a variety of morphologic configurations. Multiple feeding arterioles and draining venules are common, and autoinfarction appears to occur initially at the preretinal capillary level rather than at feeding arterioles. Arteriovenous crossings may be a preferential site for sea fan development.

Intrachoroidal microvascular abnormality: a previously unrecognized form of choroidal neovascularization

PURPOSE

To evaluate the histopathologic and histochemical characteristics of intrachoroidal microvascular abnormality.

METHODS

Forty eyes obtained at autopsy from human donors ranging in age from 20 to 91 years (25 diabetics, 15 nondiabetics) were analyzed. Choroids were processed for alkaline phosphatase flat-embedding. Vascular patterns were examined and analyzed before embedding and serial sectioning.

RESULTS

Intrachoroidal microvascular abnormality had the most prominent alkaline phosphatase reaction product of choroidal vessels. These formations appeared as ameboid or cobweb-like vascular networks (area, 0.05 to 4.6 mm2) in the choroidal stroma external to the choriocapillaris. They appeared as both single or groups of formations in the posterior pole and equatorial regions in all subjects. Intrachoroidal microvascular abnormality was found in five subjects with diabetes: four with type I diabetes mellitus, and one with type II diabetes mellitus. One subject had proliferative diabetic retinopathy, three had background retinopathy, and one had no retinopathy. Intrachoroidal microvascular abnormality was connected with all levels of choroidal vasculature. Microaneurysms were observed within intrachoroidal microvascular abnormality formations in most subjects but not in other choroidal vessels.

CONCLUSIONS

Intrachoroidal microvascular abnormality is a form of intrachoroidal neovascularization. This neovascularization has features similar to intraretinal microvascular abnormalities found in diabetic subjects but seems to form independently of the status of retinopathy. The presence of microaneurysms in intrachoroidal microvascular abnormalities and not other choroidal vessels supports the view that aneurysms may be aborted attempts at neovascularization.

Relationship of polymorphonuclear leukocytes to capillary dropout in the human diabetic choroid

Capillary dropout is an initial event in diabetic retinopathy, but the etiology is unknown. Recent evidence suggests that similar events may occur in the diabetic choroid. We have developed a method to evaluate the relationship between the polymorphonuclear leukocytes (PMNs) and capillary dropout in the human diabetic choroid using alkaline phosphatase (APase) histochemistry to label blood vessels and nonspecific esterase activity to identify PMNs. The number and distribution of PMNs in diabetic and nondiabetic choroidal capillaries (choriocapillaris) were analyzed in the flat perspective and the tissue then flat embedded in glycol methacrylate for histological sectioning. The total number of PMNs was increased within the choriocapillaris in five diabetic eyes (170.9 +/- 12.9 PMNs/mm2 of choroid) compared with five nondiabetic eyes (84.2 +/- 16.9 PMNs/mm2; P < 0.001). PMNs were almost always within blood vessel lumens and not in interstitial tissue. In the diabetic choroid, increased numbers of PMNs were present in areas of choriocapillaris with pathological changes (loss in APase activity and choroidal neovascularization) compared with nonpathological choriocapillaris (205.1 +/- 46.9 PMNs/mm2 in pathological versus 152.3 +/- 23.4 PMNs/mm2 in nonpathological areas; P < 0.001). PMNs were often queued up within the lumens of capillaries, demonstrating loss in APase activity. We have observed an increased number of PMNs in diabetic choroid compared with control nondiabetic choroids, and PMNs in diabetic choroid were associated with loss in APase activity, which was related to loss in viable endothelial cells. The results suggest that PMNs contribute to vaso-occlusive processes and endothelial cell injury in the diabetic choroid.

A rat model for sickle cell-mediated vaso-occlusion in retina

Occlusions of the retinal vasculature are the initiating event in sickle cell retinopathy. In order to understand the mechanism(s) of sickle cell-mediated occlusion, a rat model was developed. Red blood cells (RBCs) from patients homozygous for hemoglobin (Hb) S (SS) or double heterozygous for Hb S and Hb C (SC) were separated on Percoll-Larex continuous density gradients, labeled with fluorescein isothiocyanate (FITC), and delivered via the left ventricle to anesthetized, ventilated rats. Blood gas levels were altered by changing inspired gas and monitored via a femoral arterial catheter. After the RBCs circulated for 5 min, animals were perfused with heparinized saline, the eyes enucleated, and the retinas removed and processed by our ADPase flatmount technique. The retinal vasculature was visualized under dark-field illumination and the FITC-RBCs visualized by fluorescence microscopy. Greater numbers of high-density SS cells (SS4, which consist of dense, dehydrated discocytes and irreversible sickled cells) were retained in the normal rat retinal vasculature than normal-density SS cells (SS2, which have the same density as normal AA cells, but consist of reticulocytes and young cells). Retention of SS4 cells was inversely dependent on the arterial oxygen tension. Most SS4s were retained in capillaries, but a few were observed within precapillary arterioles. The retained RBCs occupied the full lumenal diameter of vessels in most cases. In contrast, very few RBCs from SC donors (normal or high density) were retained in the normal retinal vasculature and retention did not increase significantly with hypoxia. This model demonstrates that high-density SS cells, which include irreversibly sickled cells, are retained in normal rat retinal vessels and that the number retained is oxygen dependent. Furthermore, it appears that trapping, not adhesion, is responsible for retention of RBCs in the normal retinal vasculature because there was preferential retention of SS4 cells, which are known to have lower adherence propensity, and the retained RBCs blocked the full diameter of the vessel. These results also demonstrate that the mechanism of vascular obstruction by SS and SC RBCs is different because low retention of SC cells was observed. The well-known propensity of SC patients to have retinal abnormalities must involve extraerythrocytic factors like increased hematocrit, induction of adhesive molecules and integrins, etc.

Localization of vascular endothelial growth factor in human retina and choroid

OBJECTIVE

To examine the distribution and relative levels of vascular endothelial growth factor (VEGF) in the nondiabetic and preproliferative diabetic human retina and choroid.

METHODS

Immunohistochemical localization was performed on frozen sections from cryopreserved postmortem human tissue using a polyclonal antibody against VEGF and a streptavidin peroxidase system. Eyes from 5 subjects without diabetes and 8 subjects with diabetes were examined and analyzed using a 7-point immunohistochemical grading system.

RESULTS

In subjects without diabetes, weak or no VEGF immunoreactivity was associated with retinal blood vessels. In subjects with diabetes, we found significantly increased immunoreactivity in the retinal vascular endothelium and blood vessel walls. Vascular endothelial growth factor immunoreactivity was also associated with intravascular leukocytes in subjects with and without diabetes. In the choroid of subjects without diabetes, immunoreactivity was almost exclusively associated with intravascular leukocytes, whereas in diabetic subjects, immunoreactivity was localized within choriocapillaris endothelium, choroidal neovascular endothelium, and migrating retinal pigment epithelium cells.

CONCLUSIONS

The observed increase in VEGF immunoreactivity in the diabetic retina and choroid suggests that VEGF may contribute to 2 well-documented events during retinopathy: increased vascular permeability and angiogenesis.

Vasoproliferation in the neonatal dog model of oxygen-induced retinopathy

PURPOSE

To examine the time course and relative degree of proliferative response associated with revascularization after hyperoxic insult in the dog model of oxygen-induced retinopathy.

METHODS

Mitotic cell profiles (MCPs) were counted in serial cross-sections of ADPase flat-embedded retinas of air-reared control 8-, 15-, and 22-day-old dogs and of age-matched oxygen treated animals (4 days, 100% oxygen) after return to normoxia. Sectioning and analysis were performed along the radial axis of the forming primary vasculature from optic nerve head to periphery.

RESULTS

In air-reared control animals, lumenal-associated cell mitosis was low, with an average of 9.6 MCPs/mm2 of nerve fiber layer tissue in the 8-day-old dogs, 6.5 MCPs/mm2 in the 15-day-old dogs, and 8.4 MCPs/mm2 in the 22-day-old dogs. In oxygen-treated animals, however, the number of lumenal-associated MCPs was significantly higher, with an average of 52.5 MCPs/mm2 of tissue in the 8-day-old dogs, 45.1 MCPs/mm2 in the 15-day-old dogs, and 26.8 MCPs/mm2 in the 22-day-old dogs. Additionally, extracellular spaces in avascular retina were obliterated in oxygen-treated animals.

CONCLUSIONS

This study demonstrates that in the neonatal dog, revascularization after hyperoxic insult involves a period of marked vasoproliferation that peaks somewhere between 3 to 10 days after return to room air. Oxygen-induced changes in the extravascular milieu are likely to affect the pattern of reforming vasculature and may restrict growth anteriorly.

Vaso-obliteration in the canine model of oxygen-induced retinopathy

PURPOSE

To quantify the acute constrictive response of developing retinal blood vessels to hyperoxia and to examine the vaso-obliterative phase of sustained oxygen breathing in the neonatal dog model of retinopathy of prematurity.

METHODS

Seven littermates were used to examine the acute constrictive response of the developing retinal vessels to hyperoxia (30 minutes to 96 hours of 100% oxygen). ADPase retinal flatmounts were prepared, and morphometric measurements were made using computer-assisted analysis. Vaso-obliteration also was examined in three animals killed after prolonged exposure to hyperoxia (4 days of 100% oxygen) and in three room air controls using ADPase flat-embedded retinas and cross-sections. Choroids were processed for alkaline phosphatase flat-embedding.

RESULTS

After 1 hour of oxygen breathing, all vascular components showed a reduction in diameter: Arteries were reduced 27%, veins 18.3%, and capillaries 27.7%. Capillary constriction peaked by 24 hours (69.4% reduction), whereas arteries and veins continued to close. Although capillary diameters did not decrease significantly after 24 hours, the number of capillaries, as determined by percent vascular area calculations, continued to decrease in all areas through the additional 3 days of oxygen breathing. In contrast, after 4 days of hyperoxia the choriocapillaris lumenal diameters and percent vascular area did not vary significantly from controls. Analysis of sections taken through various retinal regions of these animals revealed significant decreases (40%) in the volume of the extracellular spaces available for blood vessel formation. Hyperoxia also reduced in a 55.6% decrease in the total number of cells (endothelial cells, ablumenal cells, perivascular cells) within the inner retina; however, there was no significant difference in ganglion cell counts in the two groups.

CONCLUSIONS

This study demonstrates that the pattern and severity of the reaction of developing retinal vessels to hyperoxia in the newborn dog is similar to that described for the kitten and the premature human. This response is unlike that exhibited by the newborn rat or mouse.

Enhanced expression of intracellular adhesion molecule-1 and P-selectin in the diabetic human retina and choroid

Elevated expression of intercellular adhesion molecule-1 (ICAM-1) as well as E- and P-selectin occurs on the vascular endothelium in a number of disease states and is thought to play an early critical role in the adhesion of circulating leukocytes to the endothelium. The goal of the present study was to investigate the immunolocalization of these molecules in the retina and choroid of postmortem human tissue sections from nondiabetic and diabetic subjects. Whereas ICAM-1 was localized primarily within the choriocapillaris of nondiabetic subjects, immunoreactivity in diabetics was significantly elevated throughout the choroidal vasculature and within retinal blood vessels (P < 0.05). In the choroid, P-selectin was most prominent in veins of the nondiabetic, whereas in diabetics, P-selectin was significantly elevated in arteries (P < 0.001) and veins (P < 0.05) and, in some cases, was also observed in choriocapillaris. P-selectin immunoreactivity was not observed in the retina of any subject. E-selectin immunoreactivity was not observed in choroid or retina in any subjects. Neutrophil numbers per square millimeter of tissue were significantly elevated in diabetic choroid (P < 0.05) and retina (P < 0.001). Our results demonstrate that ICAM-1 and P-selectin are constitutively expressed in the normal choroid and are upregulated in the choroidal vasculature in diabetes, but only ICAM-1 was upregulated in the retina of diabetic subjects. Increased cell adhesion molecule expression may contribute to the retinal and choroidal microangiopathy observed in diabetics by enhancing leukocyte adhesion and consequently the incidence of capillary obstruction and endothelial cell injury.

Menadione-dependent alpha glycerophosphate and succinate dehydrogenases in the developing canine retina

Reducing equivalents for the electron transport chain are generated within the mitochondria by the Krebs cycle and in cytoplasm by processes like lipid metabolism. Two mitochondrial enzymes, succinate dehydrogenase (SDH), a prominent enzyme in the Krebs cycle, and alpha-glycerophosphate dehydrogenase (alpha-GPDH), half of the glycerophosphate shuttle system for bringing reducing equivalents from cytoplasm to mitochondria, were examined enzyme histochemically to assess the contribution of each to metabolism of the developing canine retina. SDH activity, a common marker for oxidative metabolism, was insignificant at birth. By 4 days of age, activity was observed only in developing photoreceptor inner segments. By 21 days of age SDH activity was present throughout the retina, especially in photoreceptor inner segments and plexiform layers, and approached the level observed in the adult dog. Menadione-linked alpha-GPDH (M-alpha-GPDH) activity, however, was prominent in developing vasculature and outermost portion of the neuroblastic layer of the 1 day-old retina. Most notable was localization in vascular precursors, angioblasts, found distant from formed vessels in the peripheral nerve fiber layer. Retinal dependence on an oxidative metabolism in neuronal elements, as represented by SDH activity, occurs only when the vasculature is well established.

High-resolution histologic analysis of the human choroidal vasculature

PURPOSE

To develop a high-resolution histologic technique to study the postmortem human choroidal vasculature in dual perspective: vascular pattern in the flat perspective and structure in cross sections.

METHODS

Fresh whole human choroids were denuded of retinal pigment epithelium, fixed, incubated for enzyme histochemical demonstration of alkaline phosphatase (APase) activity, bleached with hydrogen peroxide, and flat-embedded in glycol methacrylate. Vascular patterns were examined and documented en bloc, and subsequent serial sectioning was performed through specific sites of interest.

RESULTS

APase staining provided excellent visualization of the entire choroidal vasculature en bloc. Reaction product was generally more prominent in the choriocapillaris and collecting venules than in veins or arterioles, whereas arteries had the least activity. Diminished activity within focal regions of the choriocapillaris was observed in the far periphery of most aged subjects and was related to loss of endothelium and capillary atrophy. Hard drusen were generally observed in clusters located near collecting venules and appeared unrelated to any underlying angiopathy, whereas basal linear and laminar deposits were most often associated with regions of capillary dropout. Choroids from patients with diabetes demonstrated angiopathic changes consisting of extensive capillary dropout, beaded capillaries, neovascularization, and Bruch's membrane degeneration.

CONCLUSIONS

The benefits afforded by this method of analysis are that choroidal vasculature can be visualized in the native state and that nonvascular structures are retained for simultaneous analysis with vascular pattern and blood vessel structure.

Determination of the mechanism of free radical generation in human aortic endothelial cells exposed to anoxia and reoxygenation

Endothelial cell-derived oxygen free radicals are important mediators of postischemic injury; however, the mechanisms that trigger this radical generation are not known, and it is not known if this process can occur in human cells and tissues. The enzyme xanthine oxidase can be an important source of radical generation; however, it has been reported that this enzyme may not be present in human endothelium. To determine the presence and mechanisms of radical generation in human vascular endothelial cells subjected to anoxia and reoxygenation, electron paramagnetic resonance measurements were performed on cultured human aortic endothelial cells using the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO). These measurements were correlated with cellular injury, xanthine oxidase activity, and alterations in cellular nucleotides. Upon reoxygenation after 60 min of anoxia, large DMPO-OH (aN = aH = 14.9 G) and smaller DMPO-R (aN = 15.8 G, aH = 22.8 G) signals were seen. Superoxide dismutase totally quenched this radical generation. The ferric iron chelator deferoxamine prevented cell death and totally quenched the DMPO-R signal with a 40% decrease in the DMPO-OH signal. Xanthine oxidase was shown to be present in these cells and to be the primary source of free radicals. While the concentration of this enzyme did not change after anoxia, the concentration of its substrate, hypoxanthine, markedly increased, resulting in increased free radical generation upon reoxygenation. Thus, reoxygenated human vascular endothelial cells generate superoxide free radicals, which further react with iron to form the reactive hydroxyl radical, which in turn causes cell death. Xanthine oxidase was the primary source of radical generation with this process triggered by the breakdown of ATP to the substrate hypoxanthine during anoxia.

Retinal and choroidal neovascularization in a transgenic mouse model of sickle cell disease

A complication of sickle cell disease is proliferative retinopathy. We investigated the eyes from a transgenic mouse model of sickle cell disease (alpha H beta S[beta MDD] type) to determine if pathological changes occurred in their retinas and choroids. One retina from each animal was processed by flat-embedding adenosine diphosphatase-reacted retinas in glycol methacrylate. The fellow eye from each animal was embedded whole in glycol methacrylate for histopathological analysis of all ocular structures. Retinal vascular occlusions resulted in nonperfused areas of retina and arterio-venous anastomoses. Intra- and extraretinal neovascularization was observed adjacent to nonperfused areas. Retinal pigmented lesions were formed by the migration of retinal pigment epithelial cells into sensory retina, often ensheathing choroidal neovascularization. The incidence of this bilateral chorioretinopathy was 30% in animals older than 15 months of age. The ocular histopathological changes we observed in the mouse model mimicked many aspects of human proliferative sickle cell retinopathy. Furthermore, this is the first genetically derived animal model for chorio-retinal neovascularization.

Measurement and characterization of free radical generation in reoxygenated human endothelial cells

The endothelial cell is thought to be an important site of free radical generation in ischemic tissues. It has been demonstrated that endothelial cells from several species generate a burst of free radical generation upon reoxygenation; however, it has been suggested that human endothelial cells are not similarly capable of generating free radicals on reoxygenation. In view of the central importance of revascularization with accompanying reoxygenation in the clinical treatment of tissue ischemia/infarction, we have performed studies to determine the presence, mechanism, and kinetics of free radical generation in human endothelial cells. Therefore, we subjected cultured human umbilical vein endothelial cells to anoxia followed by reoxygenation. Cell suspensions of 10(7) cells/ml were subjected to varying periods of anoxia and reoxygenation. On reoxygenation with addition of a 50 mM concentration of the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), after 90 min of anoxia an electron paramagnetic resonance (EPR) signal was observed consisting of 2 components: a quartet 1:2:2:1 DMPO-OH signal, aN = aH = 14.9 G, and a six-peaked DMPO-R signal, aN = 15.6 G aH = 22.9 G, whereas cells in air gave no signal. The observed signal was quenched by superoxide dismutase (SOD) or catalase. Deferoxamine decreased the measured radical signals by 40%. Cyclooxygenase blockers did not decrease radical generation, but the xanthine oxidase blocker oxypurinol did decrease radical generation by 60%.

Immunohistochemical insights into sickle cell retinopathy

Dynamic vaso-occlusive and vaso-proliferative events occur in sickle cell retinopathy. Using streptavidin peroxidase immunohistochemistry, we investigated changes in distribution and relative levels of components in the fibrinolytic system and growth factors in retina and choroid from 2 sickle cell patients: a 20 month old SS patient and a 54 year old SC patient. Antigen localization in the sickle cell patients was compared to localization from 2 non-sickle cell, non-diabetic control subjects. In the fibrinolytic system, tissue plasminogen activator (tPA) localization and immunoreactivity were comparable in all eyes, but plasminogen activator inhibitor-1 (PAI-1) immunoreactivity was elevated within the walls of retinal vessels in the sickle cell tissue. Immunoreactive fibrin was often observed within the lumen of retinal and choroidal vessels and in choroidal neo-vascularization (CNV) in sickle cell subjects. Blood vessels containing fibrin generally exhibited elevated PAI-1 immunoreactivity. Von Willebrand's factor (vWf) and basic fibroblast growth factor (bFGF) immunoreactivity in sickle cell patients were elevated in choriocapillaris and the walls of some retinal vessels. Transforming growth factor-beta 1 (TGF-beta 1) immunoreactivity was significantly lower in sickle cell choriocapillaris than in controls. In chorioretinal pigmented lesions of the SC patient, bFGF and TGF-beta 1, beta 2, and beta 3 immunoreactivity was present within migrating retinal pigment epithelial (RPE) cells. Our interpretation of the data presented in this case study is that fibrin deposition within retinal and choroidal vessels of sickle cell subjects may occur due to elevated PAI-1 activity. Moreover, vaso-occlusions of choroidal vessels may influence the expression of growth factors in choriocapillaris endothelium, which could stimulate formation of choroidal neovascularization. Finally, fibrosis and gliosis in and near chorioretinal pigmented lesions may be stimulated by RPE production of bFGF and TGF-beta's.

Dual-perspective analysis of vascular formations in sickle cell retinopathy

OBJECTIVE

To examine the sickle cell retina in dual perspective (vascular patterns en bloc and structure in serial sections) to gain new insights into sickle cell retinopathy.

METHODS

We analyzed the retinas of two patients with sickle cell disease (a 54-year-old patient with hemoglobin SC, heterozygous for the S and C mutation in the beta chain of the globin gene, and a 20-month-old patient with sickle cell anemia [SS], homozygous for the S mutation) using the previously described adenosine diphosphatase flat-embedding technique.

RESULTS

The dual-perspective analysis afforded by our technique revealed that the primary site of occlusions was located at the precapillary level. An unusual neovascular formation, the hairpin loop, was observed in both patients' retinas and appeared to result from recanalization of the wall of an occluded vessel. Many autoinfarcted pre-retinal neovascular formations were observed in the older SC patient. Two patent preretinal formations were studied in detail and their evolution appeared to be influenced by mechanical factors. The vessels appeared to have been extruded from the retina, perhaps owing to hydrostatic pressure secondary to downstream occlusions. Small pigmented lesions consisting of retinal pigment epithelial cells ensheathing channels that resembled autoinfarcted vessels were found in the eye of the SC patient.

CONCLUSIONS

This study illustrates unusual morphological features of intraretinal and preretinal neovascularization and of chorioretinal lesions in sickle cell retinopathy and suggests alternative mechanisms for their formation.

Heterogeneity in localization of isoforms of TGF-beta in human retina, vitreous, and choroid

PURPOSE

The purpose of this work was to investigate further the immunohistochemical localization of transforming growth factor (TGF)-beta 1 to photoreceptors, which we had previously observed, to elucidate the cell types of origin for TGF-beta 1, and to determine sites of localization for TGF-beta 2 and beta 3 in the posterior segment of the human eye.

METHOD

Streptavidin-peroxidase immunohistochemistry was used to localize TGF-beta antibodies in sections from cryopreserved human posterior segments from six adult donors. Two recently described polyclonal antibodies to TGF-beta 1 (anti-CC[1-30] and anti-LC[1-30]) and antibodies against TGF-beta 2 and beta 3 were employed in this study. Other studies suggest that anti-LC(1-30) antibody recognizes pre-pro-TGF-beta 1 and therefore sites of production, while anti-CC(1-30) recognizes secreted forms of TGF-beta 1.

RESULTS

Regional labeling of choriocapillaris was observed in all eyes using anti-LC(1-30) (anti-pre-pro-beta 1). Anti-CC(1-30) (anti-secr-beta 1) was localized predominantly in photoreceptor inner and outer segments in all eyes. Outer segment localization appeared identical to anti-opsin localization, indicating that this form of TGF-beta 1 is most likely intracellular. TGF-beta 2 was observed predominantly in the connective tissue of long ciliary arteries in choroid and in photoreceptor outer segments in all eyes. TGF-beta 3 was observed in isolated individual cells in choroid and retina. Vitreous hyalocytes were the only cell type examined that were immunoreactive for all four forms of TGF-beta studied.

CONCLUSION

The heterogeneity in localization of TGF-beta s in the human posterior eye suggests that TGF-beta s are produced, used, and degraded locally. TGF-beta 1 produced by the choriocapillaris may be stored or used by photoreceptors.

Immunolocalization of TGF-beta 1, TGF-beta 2, and TGF-beta 3 in the anterior segment of the human eye

PURPOSE

To determine the distribution of transforming growth factor type beta (TGF-beta) in the anterior segment of the human eye. This knowledge is important because TGF-beta may regulate various physiologic responses in the anterior segment by controlling cell proliferation and differentiation, angiogenesis, and extracellular matrix composition.

METHODS

Immunohistochemical methods were used to localize the beta 1, beta 2, and beta 3 isoforms of TGF-beta in the anterior segment of the human eye.

RESULTS

Eight of eight eyes (six eye bank specimens and two eyes enucleated because of choroidal melanoma) exhibited staining for at least one of the TGF-beta isoforms. TGF-beta 1 was found in superficial limbal epithelial cells (four of eight eyes) and in the stroma proximal to the ciliary processes (seven of eight eyes). TGF-beta 2 was found in superficial limbal epithelial cells (six of eight eyes), the conjunctival stroma (eight of eight eyes), in the ciliary processes (three of eight eyes), and in a diffuse distribution in the region of the radial and circular muscles of the ciliary body (eight of eight eyes). In addition, TGF-beta 2 was found in the stroma adjacent to the pigmented epithelium in the pars plana (eight of eight eyes). TGF-beta 3 was found in white blood cells in one of eight specimens; otherwise it was not found in the anterior segment. The corneal stroma, corneal endothelium, trabecular meshwork, iris, and ciliary epithelia did not exhibit immunoreactivity with the antibodies used in this study.

CONCLUSION

TGF-beta 1 and TGF-beta 2 have a distinct and specific distribution in the anterior segment of the adult human eye.

A new technique for visualization of the human retinal vasculature

Adenosine diphosphatase, an endothelial cell ectoenzyme that hydrolyses adenosine 5'-diphosphate to adenosine monophosphate, has been used histochemically to study the human retinal vasculature in flat mounts or as flat-embedded tissue that can be sectioned. In all retinas, reaction product was confined almost exclusively to the vasculature, with arteries having more reaction product than veins or capillaries. Adenosine diphosphatase activity was observed in endothelium, smooth-muscle cells, pericytes, and erythrocytes. In the more elaborate version of the technique, the adenosine diphosphatase-incubated retinas were flat embedded in glycol methacrylate. This allowed study of the retinal vasculature in dual perspective: en bloc with the use of dark-field microscopy and specific areas of interest histologically sectioned for further evaluation. The technique is simple and preserves angioarchitecture because the retinas are intact, and patency of the vasculature can be determined.

Increased sensitivity of the non-human primate eye to microwave radiation following ophthalmic drug pretreatment

Previous studies in our laboratory have established that pulsed microwaves at 2.45 GHz and 10 mW/cm2 are associated with production of corneal endothelial lesions and with disruption of the blood-aqueous barrier in the non-human primate eye. In the study reported here we examined ocular damage in monkeys (M. mulatta and M. fascicularis) following topical treatment with one of two ophthalmic drugs (timolol maleate and pilocarpine) that preceded exposure to pulsed microwaves. Anesthetized monkeys were sham exposed or exposed to pulsed, 2.45 GHz microwaves (10 microseconds, 100 pps) at average power densities of 0.2, 1, 5, 10, or 15 mW/cm2 4 h a day for 3 consecutive days (respective SARs were 0.052, 0.26, 1.3, 2.6, and 3.9 W/kg). Immediately before microwave exposure, one or both eyes were treated topically with one drop of 0.5% timolol maleate or of 2% pilocarpine. Following administration of a drug, we observed a significant reduction in the power-density threshold (from 10 to 1 mW/cm2) for induction of corneal endothelial lesions and for increased vascular permeability of the iris. Diagnostic procedures (in vivo specular microscopy and fluorescein iris angiography) were performed following each exposure protocol. In addition, increased vascular permeability was confirmed with horseradish peroxidase tracer techniques. Although we did not measure intraocular temperatures in experimental animals, the results suggest that a mechanism other than significant heating of the eye is involved. Our data indicate that pulsed microwaves at an average SAR of 0.26 W/kg, if administered after pretreatment with ophthalmic drugs, can produce significant ocular effects in the anesthetized primate.

Modification of membrane fluidity in melanin-containing cells by low-level microwave radiation

The treatment of a B16 melanoma cell line with 2.45-GHz pulsed microwaves (10 mW/cm2, 10-microseconds pulses at 100 pps, 1-h exposure; SAR, 0.2 W/kg) resulted in changes of membrane ordering as measured by EPR (electron paramagnetic resonance) reporter techniques. The changes reflected a shift from a more fluid-like phase to a more solid (ordered) state of the cell membrane. Exposure of artificially prepared liposomes that were reconstituted with melanin produced similar results. In contrast, neither B16 melanoma cells treated with 5-Bromo-2-Deoxyuridine (3 micrograms/day x 7 days) to render them amelanotic, nor liposomes prepared without melanin, exhibited the microwave-facilitated increase of ordering. Inhibition of the ordering was achieved by the use of superoxide dismutase (SOD), which strongly implicates oxygen radicals as a cause of the membrane changes. The data indicate that a significant, specific alteration of cell-membrane ordering followed microwave exposure. This alteration was unique to melanotic membranes and was due, at least in part, to the generation of oxygen radicals.

Altered distribution of basic fibroblast growth factor in diabetic retinopathy

Basic fibroblast growth factor (FGF) is a potent endothelial cell mitogen that has been proposed to play a role in proliferative diabetic retinopathy and other neovascular processes. Our understanding of the in vivo role of basic FGF in the pathogenesis of these disorders is limited. We studied the immunolocalization of basic FGF in 16 clinical cases of diabetic retinopathy to determine whether the normal retinal distribution of basic FGF changed during the development of diabetic retinopathy and correlated with the onset of retinal neovascularization. By using monoclonal and affinity-purified polyclonal antibodies against basic FGF and heparan sulfate proteoglycan (HSPG), we found that basic FGF colocalized with HSPG to vascular basement membranes. As the basement membranes thickened during the progression of diabetic retinopathy, the intraretinal stores of immunoreactive basic FGF and HSPG expanded. With the development of neovascularization, the colocalization of basic FGF and HSPG changed; HSPG localized to basement membranes, while basic FGF localized intracellularly, with only minimal basement membrane immunoreactivity. Incubations of the neovascular fronds with exogenous basic FGF demonstrated multiple HSPG glycosaminoglycan-binding sites for basic FGF, indicating that basic FGF had not been released from the matrix of neovascular fronds by heparitanase digestion.

Immunolocalization of tissue plasminogen activator in the diabetic and nondiabetic retina and choroid

Retinal capillary closure is a common finding in many patients with diabetic retinopathy. The cause of this capillary occlusion is unknown. Since occlusions in microthromboembolic disease can occur because of deficiencies in tissue plasminogen activator (tPA) and since systemic tPA decreases with an increasing duration of diabetes mellitus, the immunohistochemical localization of tPA in the retinas and choroids of diabetic and nondiabetic patients was investigated. The localization of tPA was confined to arteries and arterioles in peripheral retinas from nondiabetics. Both veins and arteries were positive in these choroids. Two of three noninsulin-dependent diabetics had normal levels of immunoreactivity in their retinas, and all had normal levels of immunolocalization in their choroids. All but 2 of the 12 insulin-dependent diabetic eyes (IDDM), however, had reduced levels of retinal tPA immunoreactivity which was most pronounced in their peripheral retinas. Seven eyes from patients with IDDM had no reaction product in their peripheral retinas. Two such eyes also had reduced tPA immunoreactivity in their choroidal vessels. Some tPA-positive vessels were observed in the central retinas of these eyes, but the number of positive vessels and amount of reaction product was greatly reduced compared with eyes from nondiabetic patients. These observations suggest that IDDM patients have reduced fibrinolytic activity in their retinas, which might predispose them to thromboembolic disease.

Localization of basic fibroblast growth factor to the developing capillaries of the bovine retina

The basic fibroblast growth factor (FGF) is a potent mitogen that has vascular endothelium as one of its principle target cells. Recent work has provided both the complete amino acid sequence of basic FGF and the nucleotide sequence of the genes for both human and bovine basic FGF. Although capillary endothelial cells have been shown to produce basic FGF in vitro and to deposit basic FGF in their extracellular matrix in vitro as well, no direct evidence yet exists for the distribution of basic FGF in vivo. Antipeptide antibodies were prepared against a 15-amino-acid sequence from the amino terminus of basic FGF in order to avoid cross-reactivity with acidic FGF, a protein with 55% overall homology to basic FGF. After affinity purification, these antisera were used to localize the basic fibroblast growth factor in the fetal and adult bovine retina. Immunoreactive material was found in capillaries of the inner nuclear layer, a capillary network undergoing development during the third trimester in the fetal bovine eye. Although the resolution of the technique does not permit a unique assignment of cellular localization, the presence of stain immediately adjacent to the lumen of capillaries suggests that capillary endothelial cells may produce the basic fibroblast growth factor in vivo during vascular development.

Measurement of endothelial cell free radical generation: evidence for a central mechanism of free radical injury in postischemic tissues

Oxygen free radicals have been demonstrated to be important mediators of postischemic reperfusion injury in a broad variety of tissues; however, the cellular source of free radical generation is still unknown. In this study, electron paramagnetic resonance measurements with the spin trap 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO) demonstrate that bovine endothelial cells subjected to anoxia and reoxygenation become potent generators of superoxide and hydroxyl free radicals. A prominent DMPO-OH signal aN = aH = 14.9 G is observed on reoxygenation after 45 min of anoxic incubation. Quantitative measurements of this free radical generation and the time course of radical generation are performed. Both superoxide dismutase and catalase totally abolish this radical signal, suggesting that O2 is sequentially reduced from O2-. to H2O2 to OH.. Addition of ethanol resulted in trapping of the ethoxy radical, further confirming the generation of OH.. Endothelial radical generation was shown to cause cell death, as evidenced by trypan blue uptake. Radical generation was partially inhibited and partially scavenged by the xanthine oxidase inhibitor allopurinol. Marked inhibition of radical generation was observed with the potent xanthine oxidase inhibitor oxypurinol. These studies demonstrate that endothelial cells subjected to anoxia and reoxygenation, conditions observed in ischemic and reperfused tissues, generate a burst of superoxide-derived hydroxyl free radicals that in turn cause cell injury and cell death. Most of this free radical generation appears to be from the enzyme xanthine oxidase. Thus, endothelial cell free radical generation may be a central mechanism of cellular injury in postischemic tissues.

Ocular fluorescein phototoxicity

Fluorescein angiography is one of the most commonly used diagnostic techniques in modern ophthalmology. Prior to this study, recommendations on the phototoxicity of this technique were based on light levels alone (i.e., without fluorescein present). Using a rabbit model to demonstrate retinal damage, intravenous sodium fluorescein was found to reduce the amount of blue light needed to cause a phototoxic retinal lesion almost a log unit (from 1.6 to 0.2 W/cm(2)). Intravenous fluorescein also reduced the threshold for light damage to iris and cornea in the rabbit. The results suggest that blue light exposure should be minimized when sodium fluorescein is present in ocular tissue.

Modulation of human lymphocyte proliferation by normal bovine vitreous

A heat stable antiangiogenic protein (Bovine Vitreal Protein or BVP) isolated from normal bovine vitreous and known to inhibit growth of endothelial and smooth muscle cells was studied for its in vitro effect on human lymphocyte proliferation. Unheated BVP inhibited lymphoproliferation in 12 normal, healthy donors in response to tetanus toxoid (TT) and to Concanavalin A (Con A), but had little effect on responses to irradiated allogeneic peripheral blood mononuclear leucocytes (PBML) or Pokeweed mitogen (PWM). In contrast, heated (95 degrees C/10 min) BVP strongly inhibited (more than 50%) proliferative responses to allogeneic cells, TT, and Con A, and strongly augmented responses to PWM.