Immunohistochemical detection of T-cell subsets and other leukocytes in paraffin-embedded rat and mouse tissues with monoclonal antibodies

Immunohistochemical detection of SWC3, CD2, CD3, CD4 and CD8 antigens in paraformaldehyde fixed and paraffin embedded porcine lymphoid tissue

Identification of the different cell types of the immune system is important for in situ studies on the pathogenesis of infectious diseases in various animals, including the pig. Unfortunately, many monoclonal anti-leukocyte antibodies are only useful for staining frozen tissue sections with inherent poor tissue morphology, and are not readily adapted to formaldehyde fixed and paraffin embedded tissue with well preserved morphology. Seven well characterised monoclonal antibodies against porcine leukocyte antigens were tested on neutral buffered paraformaldehyde fixed and paraffin embedded porcine tissue sections using the highly sensitive tyramide signal amplification system. Combining this method with different antigen retrieval techniques enabled us to detect CD2, CD3, CD4, CD8 and SWC3 antigen expressing cells in porcine lymphoid tissue. Thus, we describe herein methods for the detection of several major cell types of the porcine immune system in fixed tissue with optimal preservation of histological details.

Tissue-specific populations of leukocytes in semen-producing organs of the normal, hemicastrated, and vasectomized mouse

Semen HIV is separate and distinct from blood HIV and work has revealed that seminal plasma HIV particles do not arise from infected cells in semen. These findings indicate that semen-producing organs contain multiple, separate populations of HIV host cells. To test this hypothesis, we have examined leukocytes in semen-producing organs of male mice. Cells expressing F4/80 (tissue-specific macrophage marker) were abundant in testicular interstitium and as dendritic-like cells in the lumenal epithelium of the epididymis, especially the initial segment. Cells expressing CD45 (panleukocyte marker) were found rarely in the testicular interstitium, commonly in epididymal epithelium, were most abundant in the interstitium of the epididymis, and were more readily released from minced tissues than were F4/80(+) cells. Unlike the testis and epididymis, F4/80(+) cells in seminal vesicles also appeared to be CD45(+). Seminal vesicle leukocytes were restricted to the epithelium surrounding the lumen and were not released by mincing. CD11b (monocyte/B cell marker) was detected in testicular and seminal vesicle interstitium, but not in the epididymis. Hemicastration and vasectomy caused a limited redistribution of the leukocytes. These findings confirm the existence of tissue-specific populations of leukocytes in semen-producing organs and indicate that some populations are highly tissue adherent. The regionalized, tissue-adherent macrophages in the testicular interstitium, the initial segment of the caput epididymis, and the seminal vesicle epithelium suggest the existence of reservoirs of HIV-infected cells in humans that could contribute virus particles, but not infected cells, to semen and possibly blood.

Functional heterogeneity of the kupffer cell population is involved in the mechanism of gadolinium chloride in rats administered endotoxin

BACKGROUND

The purpose of this study was to determine if evidence of functional heterogeneity between subtypes of the Kupffer cell (KC) may be involved in the mechanism of the protective effect of gadolinium chloride (GdCl3) in endotoxemia.

METHODS

Rats pretreated with or without GdCl3 were administered lipopolysaccharide (LPS) or vehicle. Serum and liver tissues were collected after LPS administration for cytokine measurements and pathological and immunohistochemical evaluation.

RESULTS

After LPS administration, increases in expression of TNF-alpha and IL-6 mRNA in the liver were blunted significantly by GdCl3. In control liver tissue, ED2-positive cells were a predominant fraction, with a few ED1-positive cells, and GdCl3 eliminated only ED2-positive cells. Further, ED2-positive cells were larger in size than ED1-positive ones. Importantly, the number of ED1-positive cells in the liver was increased about threefold in the control group but not in the GdCl3 group after LPS injection. Intermediate or large KCs isolated by counterflow centrifugal elutriation showed greater capacity for phagocytosis and production of superoxide and TNF-alpha than small ones. In contrast, IL-6 production was increased to a greater extent in small than in intermediate or large cells. GdCl3 eliminated the intermediate or large KC subpopulation predominantly.

CONCLUSION

Collectively, functional heterogeneity of the KC population was involved in the mechanism of the protective effects of GdCl3 in endotoxemia. TNF-alpha derived from activated intermediate or large KCs may activate small KCs and the latter may be recruited to other organs, such as lungs and kidneys, and produce a large amount of IL-6, leading to multiple organ failure.

A nonradioisotopic endpoint for measurement of lymph node cell proliferation in a murine allergic contact dermatitis model, using bromodeoxyuridine immunohistochemistry

INTRODUCTION

The murine local lymph node assay (LLNA) was developed as an alternative to guinea pig models for the assessment of the xenobiotic contact sensitization potential. However, it would be advantageous to have an alternative endpoint to the usual radioisotopic-dependent measures. In the present study, we investigated the development of a nonradioisotopic endpoint for LLNA using immunohistochemistry.

METHODS

Female Balb/c mice were treated by the topical application of strong sensitizers, 2,4-dinitrochlorobenzene (DNCB) and toluene diisocyanate (TDI), and a strong irritant, sodium lauryl sulfate (SLS), on the dorsum of both ears once daily for three consecutive days. The proliferation of cells in the auricular lymph node and ears was analyzed by means of the labeling index (LI) of bromodeoxyuridine (BrdU) incorporation into cells.

RESULTS

Skin reactions, consisting of increased ear thickness and the presence of inflammatory cell infiltrates, were observed in mice treated with DNCB and TDI. The cell number and the weight of the lymph nodes in the mice treated with the allergens, DNCB and TDI, were increased compared to vehicle control. We observed an increase in the areas of the B220(+) cells in the lymph nodes of mice treated with allergens, as determined by immunohistochemistry. There was an increase in the percentage of B220(+) cells in mice treated with DNCB and TDI compared to the vehicle control, but not in those treated with SLS. Because we observed an increase in the percentage of B cells in the allergen-treated group, we measured the stimulation index (SI) in the cortex and medulla (C+M) of the lymph node. The SI values of the C+M in the lymph nodes of the mice treated with DNCB and TDI were increased more than threefold compared with that of the control. However, the SI of the C+M in the lymph nodes of the mice exposed to 25% SLS was not significantly increased compared to the vehicle control, although the lymph node weight of the SLS group was significantly increased.

DISCUSSION

In Balb/c mice, BrdU immunohistochemistry showed its potential use for the identification and differentiation of chemicals with the capacity to induce irritation and sensitization. The results suggest that the measurement of the SI in the cortex and medulla of the lymph node using BrdU immunohistochemistry could provide a useful method to screen irritants and allergens.

Primary herpes simplex virus type 1 infection of the eye triggers similar immune responses in the cornea and the skin of the eyelids

Herpetic stromal keratitis (HSK) and blepharoconjunctivitis in humans are thought partly to result from immunopathological responses to herpes simplex virus type 1 (HSV-1). The corneas of NIH mice were inoculated with HSV-1 (strain McKrae) and mice were examined for signs of disease and infection on days 1, 4, 7, 10, 14 and 21. The eyes and eyelids of infected and control mice were processed for immunohistochemistry and double stained for viral antigens and one of the following cell surface markers (Gr-1, F4/80, CD4, CD8, CD45R or MHC class II) or one of the following cytokines (IL-2, IL-4, IL-6, IL-10, IL-12 or IFN-gamma). All infected mice developed signs of HSK by day 4 and blepharitis by day 7 and these both persisted until day 21, when signs of resolution where apparent. Virus was detected during the first week of infection and became undetectable by day 10. Large numbers of Gr-1(+) cells (neutrophils) infiltrated infected corneas and eyelids in areas of viral antigen and CD4(+) T cells increased significantly in number after virus clearance. In both sites, the predominant cytokines were IL-6, IL-10, IL-12 and IFN-gamma, with few IL-2(+) and IL-4(+) cells. These observations suggest that the immune responses in the cornea are similar to those in the eyelids but, overall, the responses are not clearly characterized as either Th1 or Th2. In both sites, the neutrophil is the predominant infiltrating cell type and is a likely source of the cytokines observed and a major effector of the disease process.

Up-regulation of IL-18 and IL-12 in the ileum of neonatal rats with necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a common and devastating gastrointestinal disease of premature infants. Because the proinflammatory cytokines IL-18, IL-12, and interferon (IFN)-gamma have been implicated in other diseases of the small intestine, we hypothesized that these cytokines would play an important role in NEC pathogenesis. NEC was induced in newborn rats via enteral feeding with rat milk substitute and asphyxia and cold stress (RMS). Dam-fed, asphyxia- and cold-stressed littermates were used as controls (DF). After 96 h, the distal ileum was removed from all animals and processed to determine expression and localization of IL-18, IL-12, and IFN-gamma using real-time reverse transcriptase PCR and immunohistology. IL-18 and IL-12 mRNA from the RMS group were increased (p < or = 0.05) compared with DF controls, and there was a correlation between increasing IL-18 and IL-12 mRNA levels and progression of tissue damage (r = 0.629 and 0.588, respectively; p < or = 0.05). Immunohistology revealed IL-18 in the cytoplasm of villi and crypt enterocytes and IL-12-positive monocytes/macrophages were increased with disease progression (r = 0.503, p < or = 0.05). No differences in the number of IFN-gamma-positive cells were observed between groups. These data demonstrate up-regulation of IL-18 and IL-12 in experimental NEC and a correlation between production of these proinflammatory cytokines and progression of tissue damage.

Regulation of mucosal immune responses by recombinant interleukin 10 produced by intestinal epithelial cells in mice

BACKGROUND & AIMS

Interleukin (IL)-10 is a cytokine with anti-inflammatory properties. The aim of this study was to explore the effect of a site-specific delivery of IL-10 on intestinal immune responses.

METHODS

Transgenic mice were created in which IL-10 is expressed by the intestinal epithelial cells.

RESULTS

Transgenic mice showed a marked increase in the number of intraepithelial lymphocytes in the small intestine. Mucosal lymphocytes of transgenic animals produced fewer T helper type 1 cytokines than wild-type lymphocytes. By contrast, the production of transforming growth factor beta was increased. Moreover, the epithelial layer in transgenic mice was significantly enriched for CD4(+)CD25(+) T cells. Furthermore, transgenic mice had increased numbers of immunoglobulin A-producing B cells in the small intestine. These effects were local because splenic lymphocytes were not affected. Studies in models of inflammatory bowel disease showed that transgenic IL-10 was able to attenuate the acute colitis induced by dextran sodium sulfate administration or by adoptive transfer of CD4(+)CD45RB(high) splenocytes, with a modest effect on the chronic intestinal inflammation arising spontaneously in IL-10(-/-) mice.

CONCLUSIONS

These observations provide evidence for an in vivo lymphoepithelial cross talk, by which cytokines locally produced by epithelial cells can regulate immune responses in the intestine without systemic modifications.

Non-invasive induction of focal cerebral ischemia in mice by photothrombosis of cortical microvessels: characterization of inflammatory responses

In this study, we adapted the original rat photothrombosis model of Watson et al. (Ann Neurol 17 (1985) 497) for use in mice by refining the application route of the dye, illumination and stereotactic parameters. After intraperitoneal injection of the photosensitive dye Rose bengal, subsequent focal illumination of the brain with a cold light source through the intact skull led to focal cortical infarcts of reproducible size, location and geometry. Cresyl violet histology displayed well-demarcated infarcts that matured with time in a predictable manner. Microglial responses, as assessed by immunocytochemistry, against F4/80 and CD11b antigens were rapid and complete at the infarct site, but delayed and incomplete in degenerating fiber tracts and ipsilateral thalamic nuclei. In contrast to the rat, where the expression of CD4 and CD8 antigens discriminate distinct subpopulations of lesion-associated phagocytes, the expression of both markers was low to absent in the mouse model. In both rats and mice, cerebral photothrombosis shares essential inflammatory responses with focal ischemia induced by middle cerebral artery occlusion. It may provide a useful model to study functional aspects of lesion-associated and remote molecular responses in transgenic mice.

Abnormal pulmonary granuloma formation in osteopontin-deficient mice

Osteopontin is a novel cytokine that is expressed in pulmonary granulomatous disease such as sarcoidosis and tuberculosis. It can regulate macrophage and T cell migration, activation, and cytokine expression, yet its role in granuloma formation and evolution is unknown. We induced hypersensitivity pulmonary granulomas by embolizing Schistosoma mansoni eggs to the lungs of osteopontin-deficient (null mutant) mice and osteopontin-sufficient (wild-type control) mice. Granulomas from osteopontin-null animals were smaller at early time points and contained remarkably few macrophages and macrophage-derived epithelioid cells and giant cells. T cell accumulation was unaffected by osteopontin deficiency. These results demonstrate that osteopontin regulates macrophage accumulation during pulmonary granuloma formation, and may explain the impaired ability of osteopontin-deficient hosts to control mycobacterial disease.

MHC matching and mechanisms of alloactivation in corneal transplantation

BACKGROUND

In human corneal transplantation the value of matching, particularly for MHC class II, is unclear and controversial. The contribution of the direct pathway to T cell activation is also uncertain. We have determined the relative contribution of class I, II and non-MHC antigens to graft rejection and of the direct and indirect pathways to T cell activation in a rat model mimicking human incompatibilities.

METHODS

DA (RT1a) strain recipients received fully mismatched PVG (RT1c) strain grafts or grafts from one of three recombinant strains bearing DA MHC genes on a PVG background. Graft survival was assessed and the specificity of T cells generated in the draining lymph nodes was determined in mixed lymphocyte (MLR) proliferation assays. To assess the contribution of the direct pathway, fully mismatched graft were performed and allospecific proliferation was measured after depletion of recipient APC from the MLR reaction.

RESULTS

There was no significant difference in survival of grafts between the four grades of mismatch, which ranged from a full mismatch to non-MHC mismatches alone (median survival 12.5, 11, 13 and 12.5 days respectively). In conformity with clinical results, strong secondary responses were generated against targets matched for MHC with the recipient. Depletion of recipient APC from a fully allogeneic secondary MLR did not fully abrogate donor-specific proliferation.

CONCLUSIONS

Class II matching is of no benefit in this model. Strong indirect responses to non-MHC mismatches are sufficient to induce the rapid rejection, but the small numbers of class II+ cells in the donor appear sufficient to generate a direct response.

Repetitive intrathecal injections of poliovirus replicons result in gene expression in neurons of the central nervous system without pathogenesis

Poliovirus-based vectors (replicons) can be used for gene delivery to motor neurons of the CNS. In the current study, a replicon encoding green fluorescent protein (GFP) was encapsidated into authentic poliovirions, using established procedures. Intrathecal delivery of encapsidated replicons encoding GFP to the CNS of mice transgenic for the human poliovirus receptor did not result in any functional deficits as judged by behavioral testing. Histological analysis of the CNS of mice given a single intrathecal injection of poliovirus replicons encoding GFP revealed no obvious pathogenesis in neurons (or other cell types) within the CNS. The expression of GFP was confined to motor neurons throughout the neuroaxis; a time course of expression of GFP revealed that expression was detectable 24 hr postinoculation and returned to background levels by 120 hr postinoculation. A procedure was devised to allow repetitive inoculation of replicons within the same animal. Behavioral testing of animals that had received 6 to 13 independent inoculations of replicons revealed no functional deficits. Histological analysis of the CNS from animals that had received 6 to 13 sequential inoculations of replicons revealed no obvious abnormalities in neurons or other cell types in the CNS; expression of GFP was demonstrated in neurons 24 to 72 hr after the final inoculation of the replicon. Furthermore, there was no obvious inflammatory response in the CNS after the multiple inoculations. These studies establish the safety and efficacy of replicons for gene delivery to the CNS and are discussed with respect to use of replicons as new therapeutic strategies for spinal cord injuries and/or neurological diseases.

Induction of cyclooxygenase-2 in thick ascending limb cells by adrenalectomy

Adrenalectomized (ADX) and sham-operated rats received either dexamethasone (DEX) or vehicle. Renal tissue was used for morphologic analysis, assessment of cyclooxygenase-2 (COX-2) protein expression and mRNA accumulation, and quantitation of COX-2 activity. In untreated or shamoperated rats, COX-2 protein was observed in a subset of tubular epithelial cells (<2%), which were located mainly in the cortex. All COX-2-positive cells also expressed Tamm-Horsfall glycoprotein, a highly selective marker for thick ascending limb (TAL) cells. After ADX, >30% of TAL cells expressed COX-2 in a manner consistent with recruitment of COX-2-positive TAL cells toward the medulla. Treatment of ADX rats with DEX reduced the number of COX-2-positive cells to that observed in sham-operated or intact rats. COX-2 mRNA accumulation was increased by ADX and partially attenuated by treatment with DEX. Western blot analysis of cortical microsomes revealed a substantial increase in COX-2 expression in ADX rats, compared with ADX/DEX-treated, sham-operated, or intact rats. The increase in COX-2 protein expression was associated with a twofold increase in prostaglandin E(2) formation by cortical microsomes obtained from ADX rats, compared with sham-operated rats. It is concluded that ADX induces expression of enzymatically active COX-2, such that expression occurs in the cortical TAL and proceeds in a defined pattern toward the outer medullary TAL. It is suggested that ADX induces expression of TAL cells that, in the basal state, do not express COX-2 protein.

Co-localization of multiple antigens and specific DNA. A novel method using methyl methacrylate-embedded semithin serial sections and catalyzed reporter deposition

Co-localization of proteins and nucleic acid sequences by in situ hybridization and immunohistochemistry is frequently difficult as the process necessary to detect the target structure of one technique may negatively affect the target of the other. Morphological impairment may also limit the application of the two techniques on sensitive tissue. To overcome these problems we developed a method to perform in situ hybridization and immunohistochemistry on semithin sections of methyl methacrylate-embedded tissue. Microwave-stimulated antigen retrieval, signal amplification by catalyzed reporter deposition, and fluorescent dyes were used for both techniques, yielding high sensitivity and excellent morphological preservation compared to conventional paraffin sections. Co-localization of in situ hybridization and immunohistochemistry signals with high morphological resolution was achieved on single sections as well as on adjacent multiple serial sections, using computerized image processing. The latter allowed for the co-localization of multiple antigens and a specific DNA sequence at the same tissue level. The method was successfully applied to radiation bone marrow chimeric rats created by transplanting wild-type Lewis rat bone marrow into TK-tsa transgenic Lewis rats, in an attempt to trace and characterize TK-tsa transgenic cells. It also proved useful in the co-localization of multiple antigens in peripheral nerve biopsies.

Role of macrophages in nephrolithiasis in rats: an analysis of the renal interstitium

Interstitial calcium oxalate (CaOx) crystals can be found in primary oxalosis and in secondary hyperoxaluria. In a rat model for nephrolithiasis, we investigated whether such crystals can be removed by the surrounding interstitial cells. CaOx crystals were induced by a crystal-inducing diet based on ethylene glycol (EG) and ammonium chloride (CID). Both lithogenic compounds were added to the drinking water. After 9 days, the animals received normal drinking water for 2 days. Using this CID, only the interstitial crystals are retained. Subsequently, half of the population remained on normal drinking water (normo-oxaluria), whereas the other half received a low dose of EG alone (chronic hyperoxaluria). The rats were killed at regular times thereafter. The results showed that the kidney-associated oxalate significantly declined during normo-oxaluria, but remained high during chronic hyperoxaluria. Interstitial cells positive for the leukocyte common antigen (CD45; which identifies all types of leukocytes), the ED1 antigen (which is specific for monocytes and macrophages), and the major histocompatibility class II antigen (MCHII), respectively, had increased in number, with minor differences between both rat populations. The cells around the interstitial crystals were mostly positive for ED1. Multinucleate giant cells were regularly observed. These cells were positive for CD45 and ED1 and sometimes also for MCHII. The crystals in these cells were moderately positive for acid phosphatase and carbonic anhydrase II. It is concluded that interstitial CaOx crystals can be removed under normo-oxaluric conditions and that, in all likelihood, macrophages and multinucleate giant cells are involved in that process.

Anti-rat CD45RA monoclonal antibodies cross-react with glucagon

Anti-rat CD45RA monoclonal antibody (MAb) has been used as a marker for rat B-lymphocytes (B-cells). When we applied the MAb to identify B-lymphocytes among immune cells infiltrating pancreatic islets of the BB rat, which is an animal model for human type 1 diabetes mellitus, a subpopulation of islet cells was immunostained as well. Our immunohistochemical investigations demonstrated that the stained islet cells are pancreatic alpha-cells and the MAb cross-reacts with glucagon.

Therapeutic effect of intracolonically administered nuclear factor kappa B (p65) antisense oligonucleotide on mouse dextran sulphate sodium (DSS)-induced colitis

Cytokines such as IL-1, tumour necrosis factor-alpha (TNF-alpha), IL-6 and IL-8 are increased in inflamed colonic mucosa after administration of mouse DSS. Nuclear factor kappaB (NF-kappaB) is a transcription factor which regulates the expression of these cytokine genes. The effect of intracolonically administered NF-kappaB (p65) antisense phosphorothioate oligonucleotide was examined in mouse DSS-induced colitis using drinking water containing 5% DSS. When antisense oligonucleotide was given on day 0, the disease activity index (DAI) representing clinical symptoms improved and the histological score decreased; furthermore, IL-1, IL-6, and TNF-alpha concentrations in rectal mucosa were lower compared with the control group. Clinical and histological improvement was also observed when antisense oligonucleotide was begun on day 2 but not on day 7. In addition, the distribution of antisense oligonucleotides was investigated by confocal laser microscopy. In colonic mucosa, oligonucleotides were predominantly localized to cells in the lamina propria, but also in the epithelium. Western blot analysis using homogenized rectal mucosa showed the decreased expression of NF-kappaB p65 in the antisense oligonucleotide-treated group, although it was increased in the colitis group. These results suggest that intracolonic administration of NF-kappaB antisense oligonucleotide may be effective in ulcerative colitis.

Nitric Oxide Participates in the Recovery of Normal Jejunal Epithelial Ion Transport Following Exposure to the Superantigen, Staphylococcus aureus Enterotoxin B

Bacterial superantigens (SAgs) are potent T cell activators. Mice treated 4 h previously with the SAg, Staphylococcus aureus enterotoxin B (SEB), display reduced ion transport (assessed by short circuit current) responses to prosecretory stimuli, which normalize 24 h posttreatment. Here, mice were treated with SEB alone or in combination with an inhibitor of the inducible form of NO synthase (iNOS), l-NIL. Subsequently, jejunal iNOS expression was detected by immunohistochemistry, ion transport was evaluated in Ussing chambers, and serum levels of TNF-α and IFN-γ were measured by ELISA. SEB-treated mice had increased epithelial iNOS immunoreactivity, and numerous iNOS-positive CD3+ T cells occurred in their mucosa and submucosa. Concomitant treatment with l-NIL did not affect the reduced short circuit current responsiveness to electrical nerve stimulation or the prosecretory agents, carbachol and forskolin, that occurred 4 h post-SEB (5 μg) treatment. However, Isc responses in l-NIL- plus SEB-treated mice were still significantly reduced 24 h posttreatment, indicating a role for NO in the restoration of normal ion transport following exposure to SAgs. The prolongation of epithelial ion transport abnormalities correlated with elevated serum levels of TNF-α and IFN-γ in mice treated 24 h previously with l-NIL plus SEB compared with those in controls and SEB-only-treated mice. Additionally, mice treated with l-NIL plus SEB and TNF-α- or IFN-γ-neutralizing Abs displayed normal jejunal ion transport characteristics 24 h posttreatment. We conclude that NO mobilization is important in the homeostatic recovery response following immune stimulation by SAgs and that the beneficial effect of NO in this model system is probably via regulation of TNF-α and IFN-γ production.

Calcium oxalate nephrolithiasis: effect of renal crystal deposition on the cellular composition of the renal interstitium

Urinary calcium oxalate (CaOx) crystals and crystal agglomerates are normally harmlessly excreted, but in nephrolithiasis they are retained by tubular epithelial cells and shifted into the renal interstitium. This crystalline material induces an inflammatory response consisting of an increase in the number of interstitial cells and an expansion of the extracellular matrix. The newly arrived cells either derive from the blood or the connective tissue or they are formed by local proliferation. Identification of the cells that surround the interstitial crystals is a first step in investigating the question of whether the interstitial cells could remove the crystalline material. Therefore, we performed an immunohistochemical study on the kidneys of rats made hyperoxaluric by ethylene glycol (EG) and ammonium chloride (AC). Attention was paid to expression of the leukocyte common antigen (LCA), which identifies all types of leukocytes, the ED1 antigen, which is specific for monocytes and macrophages, and the major histocompatibility class II antigen (MHC II), which is present on dendritic cells, B lymphocytes, and activated macrophages. The results obtained were compared with those seen in two human kidney specimens with acute and chronic oxalosis. In both rat and humans, macrophages and multinucleated giant cells are the major cells that encapsulate the interstitial crystals. This similarity in response underlines the relevance of the rat nephrolithiasis model. The rat experiments showed, furthermore, that the number of interstitial crystals and the amount of biochemically measured kidney-associated oxalate both decrease with time, if the nephrolithiatic agents EG and AC are omitted from the drinking water. Further studies must clarify whether macrophages and multinucleated giant cells are able to remove the interstitial crystals and how these cells are recruited at the inflammatory site.

Cytokine expression in the rat central nervous system following perinatal Borna disease virus infection

Borna disease virus (BDV) causes central nervous system (CNS) disease in several vertebrate species, which is frequently accompanied by behavioral abnormalities. In the adult rat, intracerebral (i.c.) BDV infection leads to immunomediated meningoencephalitis. In contrast, i.c. infection of neonates causes a persistent infection in the absence of overt signs of brain inflammation. These rats (designated PTI-NB) display distinct behavioral and neurodevelopmental abnormalities. However, the molecular mechanisms for these virally induced CNS disturbances are unknown. Cytokines play an important role in CNS function, both under normal physiological and pathological conditions. Astrocytes and microglia are the primary resident cells of the central nervous system with the capacity to produce cytokines. Strong reactive astrocytosis is observed in the PTI-NB rat brain. We have used a ribonuclease protection assay to investigate the mRNA expression levels of proinflammatory cytokines in different brain regions of PTI-NB and control rats. We show here evidence of a chronic upregulation of proinflammatory cytokines interleukin-6, tumor necrosis factor alpha, interleukins-1alpha, and -1beta in the hippocampus and cerebellum of the PTI-NB rat brain. These brain regions exhibited only a very mild and transient immune infiltration. In contrast, in addition to reactive astrocytes, a strong and sustained microgliosis was observed in the PTI-NB rat brains. Our data suggest that CNS resident cells, namely astrocytes and microglia, are the major source of cytokine expression in the PTI-NB rat brain. The possible implications of these findings are discussed.

Reactivation of herpes simplex virus type 1 in the mouse trigeminal ganglion: an in vivo study of virus antigen and cytokines

Reactivation of herpes simplex virus type 1 (HSV-1) in the trigeminal ganglion (TG) was induced by UV irradiation of the corneas of latently infected mice. Immunocytochemistry was used to monitor the dynamics of cytokine (interleukin-2 [IL-2], IL-4, IL-6, IL-10, gamma interferon [IFN-gamma], and tumor necrosis factor alpha [TNF-alpha]) and viral antigen production in the TG and the adjacent central nervous system on days 1 to 4, 6, 7, and 10 after irradiation. UV irradiation induced increased expression of IL-6 and TNF-alpha from satellite cells in uninfected TG. In latently infected TG, prior to reactivation, all satellite cells were TNF-alpha+ and most were also IL-6(+). Reactivation, evidenced by HSV-1 antigens and/or infiltrating immune cells, occurred in 28 of 45 (62%) TG samples. Viral antigens were present in the TG in neurons, often disintegrating on days 2 to 6 after irradiation. Infected neurons were usually surrounded by satellite cells and the foci of immune cells producing TNF-alpha and/or IL-6. IL-4(+) cells were detected as early as day 3 and were more numerous by day 10 (a very few IL-2(+) and/or IFN-gamma+ cells were seen at this time). No IL-10 was detected at any time. Our observations indicate that UV irradiation of the cornea may modulate cytokine production by satellite cells. We confirm that neurons are the site of reactivation and that they probably do not survive this event. The predominance of TNF-alpha and IL-6 following reactivation parallels primary infection in the TG and suggests a role in viral clearance. The presence of Th2-type cytokines (IL-4 and IL-6) indicates a role for antibody. Thus, several clearance mechanisms may be at work.

Immune responsiveness of lymphotoxin-alpha-deficient mice: two reconstitution models

The effects of lymphotoxin-alpha (LT-alpha) deficiency on mucosal immune status has not been defined. We utilized severe combined immunodeficiency (scid) mice as recipients of both mutant and wild-type whole splenocytes to determine whether lymphocytes from mutant mice had impaired homing ability. We also utilized irradiated mutant mice as recipients of wild-type whole splenocytes to determine whether lymphoid tissue anlages had, indeed, failed to develop as a consequence of LT-alpha deficiency. Subsequently, all mice were immunized orally with an attenuated strain of Salmonella typhimurium and mucosal IgA responses were monitored. The data presented here demonstrate that scid recipients generate mucosal responses equally well when reconstituted with mutant or wild-type lymphocytes. In contrast, reconstitution of mutant mice with wild-type cells failed to affect the efficiency of their mucosal immunity. The mutant phenotype, therefore, appears to involve neither impaired lymphocyte homing nor function in the generation of mucosal immunity. However, the mutant phenotype and immune responsiveness cannot be transformed merely by the provision of LT-alpha-expressing donor cell populations. The consequence of LT-alpha deficiency on mucosal immune responsiveness appears to be due to the lack of gut-associated lymphoid tissues, which may include the spleen, in mutant mice.

The spleen and organized lymph nodes are not essential for the development of gut-induced mucosal immune responses in lymphotoxin-alpha deficient mice

Lymphotoxin knock-out (KO) mice generate specific immune responses to orally administered immunogens despite having neither gut-associated nor peripheral lymphoid tissues. The spleen, therefore, was expected to play a role in the generation of immune responses in these KO mice. KO and wild-type (wt) mice were splenectomized and orally immunized with Salmonella typhimurium. Splenectomy produced the most profound effects on serum and fecal IgA levels in KO mice. Total and antigen-specific serum and fecal IgA were increased in splenectomized wt mice but decreased in splenectomized KO mice. Antigen-specific serum IgG was decreased in both KO and wt splenectomized mice while total IgG increased in splenectomized wt mice. Both splenectomized wt and KO mice demonstrated a compensatory expansion of the lamina propria compartment characterized by a significant increase in the number of IgA spot-forming cells. KO mice demonstrated further compensation for the loss of the spleen in the accelerated development of ectopic lymphoid tissues. We conclude that the spleen plays a prominent role as a lymphoid organ in KO mice but its removal does not abolish immune responsiveness. Residual immune responsiveness in splenectomized KO mice following oral immunization appears to be due to expansion and/or development of alternate effector compartments.

Immunohistochemical detection of cytokines in paraffin-embedded mouse tissues

We have successfully developed a method for the immunohistochemical detection of interleukin 2 (IL-2), IL-4, IL-6, IL-10O, IFNgamma and TNFalpha using monoclonal antibodies (MAb), in sections of mouse tissue embedded in paraffin wax. The method involved fixation in periodate-lysine-paraformaldehyde (PLP), rapid dehydration and infiltration under vacuum with paraffin wax at 54 degrees C. Comparative observations demonstrated that the method gives equivalent or better results than formaldehyde fixed, frozen sections. Since reliable controls, both positive and negative, are paramount for interpretation of immunohistochemical staining, such controls were determined. The following tissues were shown to be suitable as positive controls when using paraffin-embedding: spleen for the detection of TNFalpha, small intestine for IL-2, IL-4 and IL-10, and HSV-1 infected eyes for IL-6 and IFNgamma. We conclude that PLP fixation and low temperature paraffin-embedding is a method which provides both preservation of excellent tissue morphology and reliable immunohistochemical identification of cytokines. These attributes will be invaluable in a wide variety of experimental situations.

Renal identification of cyclooxygenase-2 in a subset of thick ascending limb cells

The prostaglandin G2/H2 synthase (cyclooxygenase, COX) is a key regulatory enzyme of prostanoid synthesis pathway. The message-encoding COX isoenzymes (constitutive COX-1 and inducible COX-2) have been described in the rat kidney. However, there is scarce information on the localization of COX-2 in the kidney, although it has been recently reported to be localized in the macula densa. The present study was designed to evaluate the localization of COX-2 in adult rat kidneys. Normal rat kidneys (n=10) were fixed in Bouin and were immunostained with specific antibodies against COX-2 by the peroxidase method. The cellular origin of COX-2 was assessed by the immunostaining of serial consecutive sections with antibodies against Na-K-ATPase, Tamm-Horsfall glycoprotein, H-K-ATPase, kallikrein, and macrophages. COX-2 was consistently observed in a subset of tubular cells located in the cortex and in the outer medulla. The staining of serial sections showed that the COX-2+ cells contained both Na-K-ATPase and Tamm-Horsfall, indicating that they corresponded to thick ascending limb (TAL) cells. They were observed at a considerable distance from the corresponding macula densa, although occasionally they were observed close to glomeruli. The COX-2 staining in the TAL cells was not abolished by dexamethasone treatment (1 to 20 mg/kg), suggesting its constitutive expression in normal kidneys. The presence of COX-2 in TAL (a tubular segment postulated to be devoid of COX-1) may contribute to the handling of ions through local production of prostaglandins.

Single-organism model of host defense against infection: a novel immunotoxicologic approach to evaluate immunomodulatory drugs

The immunotoxicologic effects of drugs on host defense have been studied widely using various animal models of infection. Here we describe a new approach to testing host defense by using a single organism (Candida albicans) in CBA/J mice. The model is configured to test 3 effector systems via different routes of inoculation to stimulate different effector arms of the immune response. Nonspecific immunity was evaluated by C. albicans colony-forming unit (CFU) count from the spleen at 2 hr (uptake) and > or = 22 hr (clearance) following intravenous inoculation. Cell-mediated immunity was assessed by CFU count from an intramuscular injection site 6 days postinoculation. Humoral immunity was assessed by anti-Candida antibody titer, following multiple subcutaneous immunizations with C. albicans. Finally, overall immunity was evaluated following intravenous injection using survival as the endpoint. Histopathological, immunohistochemical, and electron microscopic evaluation of selected tissues revealed the involvement of the expected cell types in the different effector systems. Several immunomodulatory drugs--dexamethasone, cyclosporine, liposomal muramyltripeptide phosphatidylethanolamine, and SK&F 105685--were evaluated in the C. albicans model. Dexamethasone impaired host defense against C. albicans by suppressing all endpoints measured. Similarly, cyclosporine showed broad immunosuppressive activity, with the exception of yeast uptake from the spleen. In contrast, muramyl tripeptide-phosphatidylethanolamine enhanced all but cell-mediated immunity to C. albicans. SK&F 105685 displayed both stimulatory and inhibitory effects on immune responses to the infection. Our studies demonstrate that a single organism-based approach can be a useful method for evaluating the immunological hazards of drugs on host resistance to infection.