Platelet shape change and cytoskeletal reorganization on polyurethaneureas

Understanding how platelet activation responses are affected by polymers having varied surface physicochemical properties can lead to improved materials for vascular applications. The in vitro responses of human platelets were studied upon adherence to four polyurethaneureas with different soft segments, as well as to Biomer, and to Formvar. Platelets were observed by video-enhanced light microscopy (VLM) as they adhered to polymer films. Platelets were subsequently prepared for high-voltage transmission electron microscopy (HVEM) to view the cytoskeleton and other ultrastructural features. Scanning electron microscopy (SEM) was then used to characterize cell surface morphology and to survey platelet populations. Shape change and cytoskeletal reorganization differed on the various surfaces. The extent of shape change and cytoskeletal reorganization was related to polyurethane surface energetic properties. While the most extensive shape change was observed on the hydrophilic and polar Formvar surface, the least shape change was observed on a polyethylene oxide soft segment polyurethane with similar surface-water energetic properties. Therefore properties other than surface-water energetics must be involved in determining platelet responses to different classes of polymers. HVEM also showed that cytoskeletal reorganization proceeded to completion only on Formvar. Polyurethane adherent platelets, although appearing fully spread by SEM or VLM, never exhibited complete cytoskeletal reorganization.

Increased plasma carnitine in trauma patients given lipid-supplemented total parenteral nutrition

The purpose of this study was to determine the effects of altering the fuel substrate mix of total parenteral nutrition (TPN) on plasma and urinary carnitine in trauma patients. TPN solutions were either 100% carbohydrate (CHO) based or lipid based (70% CHO, 30% lipid). There were statistically significant (p less than 0.05) increases in plasma levels of free carnitine, short-chain acyl carnitine, and total carnitine in trauma patients receiving lipid-based TPN. No significant differences in urinary carnitine excretion were noted between groups. We conclude that the use of lipids in the TPN of trauma patients leads to an alteration in plasma carnitine metabolism.

Ex vivo platelet deposition on fibronectin-preadsorbed surfaces

Temporal platelet deposition profiles of canine plasma fibronectin (CPFN) adsorbed to different polymers ex vivo and the in vitro characteristics of CPFN adsorption were studied in an attempt to correlate the two. The maximum platelet deposition (gamma pltmax) obtained at a protein preadsorption time of 30 min was greater than that obtained using an adsorption time of 120 min for all surfaces studied. At 30 min of preadsorption, gamma pltmax was 520,560 and 1230 platelets/1000 micron2 on Biomer, polyethylene (PE) and oxidized PE (OXPE), respectively. In contrast, the platelet deposition at 120 min. of fibronectin preadsorption was about 60 approximately 90 platelets/1000 micron2 on all polymers studied. The surface concentrations of adsorbed CPFN measured using 125I-CPFN, were in the order PE greater than OXPE greater than Biomer. The adsorbed protein concentration increased with increasing adsorption time. The surface distribution of adsorbed CPFN was visualized with antibody-labelled colloidal gold and scanning electron microscopy. The extent of staining was lowest on PE, greater on Biomer, and highest on OXPE, roughly similar to the order of platelet deposition. Platelet deposition ex vivo appears to correlate with the immunogold-stainable-adsorbed protein rather than with the total amount of adsorbed protein.

Vascular changes in popliteal lymph nodes due to antigen challenge in normal and lethally irradiated mice

The microvascular system of the murine popliteal lymph node was investigated using scanning electron microscopy of microcorrosion casts. Time-dependent changes in the microvasculature following regional antigen challenge in normal and lymphocyte-depleted mice were studied. Normal lymph node microvasculature exhibited a significant increase in both the vascular bed and post-capillary venules containing high-endothelium in response to antigen challenge. Lymph nodes of lymphocyte-depleted mice showed no microvascular size increase following antigen challenge and a reduction in the amount of high-endothelium was observed.

Colloidal gold labelling of fibrinogen receptors in epinephrine- and ADP-activated platelet suspensions

It has been generally accepted for over twenty years that epinephrine stimulates platelet aggregation without inducing shape change. However, it has been recently reported that discoid platelets are not recruited into ADP- or epinephrine-stimulated aggregates. Previous work in our laboratory has suggested that platelet shape change is necessary for the binding of fibrinogen to its surface receptor, which is a prerequisite for platelet aggregation. These studies seem to indicate that epinephrine-induced platelet aggregation does involve shape change. To investigate this possibility, the extent of shape change and fibrinogen binding in suspensions of epinephrine- and ADP-activated and control platelets was assessed by scanning electron microscopy (SEM). Platelets were incubated with 20 microM epinephrine, 20 microM ADP, or vehicle and labelled with 18 nm gold beads conjugated to fibrinogen or to a monoclonal antibody directed against the glycoprotein IIb/IIIa complex which comprises the fibrinogen receptor. Results indicate that shape change does occur in epinephrine-activated platelets as well as ADP-activated platelets. Although GP IIb/IIIa was shown to be present on both discoid and shape-changed, pseudopodial platelets, a significant degree of fibrinogen binding did not occur earlier than the pseudopodial stage in either activated or control suspensions. Platelet aggregation studies showed that the majority of platelets involved in aggregates had changed shape in both ADP- and epinephrine-treated platelet suspensions. These studies suggest that epinephrine- and ADP-induced platelet aggregation occurs via the exposure of fibrinogen receptors on shape-changed platelets.

Utilization of immunogold labeling to compare the adsorption behavior of fibrinogen, fibronectin and albumin on polymers

Immunogold labeling followed by scanning electron microscopy (SEM) was used to examine the surface distribution of adsorbed plasma proteins. Adsorption was performed under various conditions on six different polymers; [low density polyethylene (PE), chromic acid-oxidized PE (OXPE), solution grade Biomer (SB), Teflon-(FEP), a laboratory synthesized polyurethane containing some zwitterions (ZW) and a polydimethylsiloxane based polyurethane (ZS) also containing zwitterions]. The proteins used were purified human and canine fibrinogen, fibronectin, and serum albumin. The immunogold staining technique was successful in the labeling of the adsorbed proteins. The adsorbed proteins were distributed differently on the polymers selected. Human and canine fibrinogen were found to cover all surfaces in a dense, uniform fashion. Albumin covered most surfaces in a less uniform fashion and on the zwitterionomers covered only a portion of the surface, leaving large bare patches. Fibronectin appeared to deposit unevenly, forming a network on part of the surface and uniformly coating other parts.

Expression of major histocompatibility complex antigens on macrophages: correlative study using flow cytometry, radioimmunoassay, and colloidal gold immunolabeling

Correlative scanning electron microscopy (SEM), radioimmunoassay (RIA), and flow cytometric analysis were used to characterize levels of class I and class II major histocompatibility complex-encoded (MHC) antigen expression on peritoneal exudate cells of mice chronically infected with Chlamydia psittaci. Analysis of peritoneal macrophages by all three techniques revealed a marked induction of H-2 K,D (class I) and I-A, I-E (class II) antigens on cells from infected C3H mice when compared to uninfected controls. Scanning electron micrographs further document that the increases in class I and II MHC antigens are due to an increase in Ia/H-2 bearing cells as well as an increase in MHC molecules/cell. These immune macrophages have a flattened morphology, almost completely devoid of the membrane ruffles and villi which are characteristic of control peritoneal macrophages. These studies suggest that while both flow cytometry and RIA can provide an accurate quantitative estimate of antigen expression in a cell population, the immunogold labeling technique can allow visualization of individual cells and additional analysis of the topographical distribution of cell surface antigens.

Correlative light and electron microscopy of platelet adhesion and fibrinogen receptor expression using colloidal-gold labeling

Differences in the shape change responses of platelets to various polymers may determine the thrombotic potential of these materials. Substrate-dependent variation in the expression and motility of the platelet fibrinogen receptor may underlie these differences due to this ligand's essential role in platelet aggregation. In this study we examine platelet activation on polyetherurethaneureas (PEUUs) presently being evaluated for vascular prosthetic applications. These polymers are prepared as 50-100nm thin films suitable as substrates for consecutive light microscopy, high voltage electron microscopy (HVEM), and SEM. 18nm colloidal gold coupled to fibrinogen permits visualization of that receptor's motility in living cells by video-enhanced light microscopy. Subsequent HVEM and SEM of identified cells provides correlative ultrastructure and surface morphology. The use of these novel support films coupled with the multiple modes of microscopy and colloidal gold labeled ligands permits in depth study of the molecular biology of cell adhesion to materials with varied, and known, surface properties. The motility of the platelet fibrinogen receptor was related to the extent of cytoskeletal reorganization, which, in turn, was influenced by polymer surface energetics. Platelets adherent to more hydrophobic PEUUs had greater receptor mobility and receptor redistribution than platelets adherent to more hydrophilic PEUUs. The most extensive receptor motility and redistribution was observed on Formvar, a non-PEUU with low surface-water energy, suggesting that additional surface properties are of importance in determining platelet spreading and fibrinogen receptor motility.

Trifluoperazine inhibition of fibrinogen receptor redistribution in surface activated platelets: correlative video-enhanced differential interference contrast light microscopic, high voltage electron microscopic and scanning electron microscopic studies

Video-enhanced differential interference contrast (VDIC) light microscopy in conjunction with fibrinogen labelled colloidal gold was employed as a probe to follow the mobility of the fibrinogen receptor on platelets. Correlative studies by both high voltage and scanning electron microscopy confirms localization of labels relative to platelet ultrastructural and surface characteristics, respectively. Treatment of platelets with trifluoperazine prior to and after incubation with fibrinogen-gold labels results in a concentration dependent inhibition of receptor movement. The results obtained from this study suggest that phosphorylation of myosin by the Ca++-calmodulin dependent enzyme, myosin-light chain kinase, is important in the fibrinogen redistribution that occurs during platelet activation.

Surface characterization of biomaterials by immunogold staining--quantitative analysis

The labeling of target proteins by immunogold particles has been analyzed based on Einstein's law of Brownian motion. The theory was confirmed from the experiments which employed antifibrinogen gold markers to label fibrinogen molecules adsorbed on the polyethylene surface. The theory predicts that the degree of labeling depends on the concentration of gold markers, temperature, medium viscosity, size of gold markers, and staining time. Of these factors most important is the concentration of immunogold particles. Small change in the marker concentration results in a significant variation in the staining efficiency when other variables are kept constant. The effect of temperature is always accompanied with that of the medium viscosity. There is a linear relationship between the degree of labeling and the temperature when the viscosity effect is combined. The staining of fibrinogen molecules adsorbed on the polyethylene surface at three different temperatures shows a temperature dependence which is in close agreement with the theory. The degree of labeling is inversely related to a square root of the size of gold markers. This analysis makes it possible to maximize the staining sensitivity and to improve the reproducibility of the labeling. Thus, the immunogold staining under a well defined condition allows quantification as well as positive identification and localization of target proteins. This technique has been used to study protein adsorption on biomaterials.

Scanning microscopy of colonic mucin during carcinogenesis: is it clinically applicable?

The integrity of the colonic mucin layer has been reported to be altered during carcinogenesis in both humans and rodents. Prior to attempting scanning microscopic techniques on colonic mucosa of patients at high risk to develop colorectal cancer, these procedures were performed on colonic mucosa from rats with chemically induced colon cancers. Substantial technical difficulties in preparation and serious subjectivity in interpretation of the scanning micrographs were encountered. The major technical problem was the unpredictable retention of the mucin layer upon both normal and cancerous mucosae. Visual interpretation of the integrity or disruption of the mucin layer with the scanning electron microscope revealed variable fenestration and fraying of the mucin in both normal and cancerous colons. Our findings suggest that scanning electron microscopy of colonic mucin may not be a reliable screening procedure for (pre)cancerous changes in human colonic mucosae.

Inhibition of canine platelet aggregation by barbiturates

The ability of barbiturates to affect in vitro platelet aggregation of canine platelets was examined. Platelet-rich plasma was incubated with thiamylal, pentobarbital, and barbital for 10 minutes before the addition of the aggregating stimulus. All three barbiturates produced a concentration-related inhibition of platelet aggregation induced by adenosine diphosphate (ADP) and collagen. The inhibitory effect of the barbiturates could not be overcome by increasing the concentration of extracellular calcium. In contrast to ADP- and collagen-induced aggregation, no inhibitory effect was observed on aggregation initiated by A23187, 12-O-tetradecanoylphorbol-13-acetate, or phospholipase C. In further studies, the ADP-induced rise in free cytosolic calcium was blocked by the barbiturates. These findings suggest that barbiturates may interfere with the rise in internal calcium associated with agonist-receptor stimulation of platelets.

The influence of preadsorbed canine von Willebrand factor, fibronectin and fibrinogen on ex vivo artificial surface-induced thrombosis

We have examined the effects of preadsorption of several canine plasma proteins on surface-induced thrombogenesis in a canine ex vivo model. Our technique allowed determination of initial deposition and subsequent embolization of 51Cr-labeled platelets and 125I-fibrinogen onto and from polymeric arterio-venous shunts in non-anticoagulated canines. Segments of the tubing were removed at various time points between 2 and 120 minutes of blood contact for examination of the morphology of the thrombus by scanning electron microscopy. Thrombus deposition was measured on uncoated plasticized poly(vinyl chloride) (PVC) and PVC precoated with canine von Willebrand factor (vWF), fibronectin, partially purified fibrinogen (fibrinogen which contained vWF and fibronectin as impurities), or purified fibrinogen (fibrinogen which had been further purified to remove fibronectin and vWF). Preadsorption of all proteins studied enhanced the thrombogenic response relative to that of the uncoated surface. Precoating with vWF or partially purified fibrinogen resulted in the deposition of the greatest number of thrombi, and embolization was slower than on shunts precoated with canine fibronectin or purified fibrinogen. The deposition-embolization profiles for the fibronectin and purified fibrinogen-coated surfaces were similar. The amount and time sequence of initial adhesion and spreading of platelets was related to the extent and time sequence of peak thrombus formation. The partially purified fibrinogen-coated and vWF-coated surfaces had more adhered and spread platelets at the earliest time points and a greater number of larger thrombi at the peak deposition times. The slowest rate of platelet adhesion and spreading was seen on the purified fibrinogen-coated surface. White blood cells were present very early on surfaces precoated with vWF and partially purified fibrinogen, and were present prior to embolization on all surfaces. Major conclusions from this work indicate that, although fibrinogen and fibronectin promote thrombogenesis when adsorbed to a surface, vWF is even more active in promoting platelet deposition and in anchoring thrombi to the surface of biomaterials. Thus, differences in vWF adsorption to biomaterials may be a determinant of surface-induced thrombogenesis.

Identification of feline monocytes and neutrophils as effector cells in antibody-dependent cellular cytotoxicity: sequential analysis, using light microscopy, histochemistry, and scanning electron microscopy

Feline monocytes and neutrophils functioned as effector cells in antibody-dependent cellular cytotoxicity (ADCC) against antibody-coated chicken erythrocytes. Using light microscopy, effector cell populations were identified in effector-target cell interactions, with further characterization of these identical individual effector cells by histochemical evaluations and scanning electron microscopy. Monocytes and neutrophils, but not lymphocytes, were observed attacking target cells. Carbonyl iron depletion of monocytes and neutrophils from peripheral blood leukocytes caused a marked reduction from a mean of 62% to 3.6% lysis in ADCC as measured by a 4-hour 51Cr release assay. Effector cells functioning in the ADCC reaction were visualized, using sequential analysis and light microscopy, histochemistry, and scanning electron microscopy.

Redistribution of the fibrinogen receptor of human platelets after surface activation

We investigated the whole cell distribution of the platelet membrane receptor for fibrinogen in surface-activated human platelets. Fibrinogen-labeled colloidal gold was used in conjunction with platelet whole mount preparations to visualize directly the fibrinogen receptor. Unstimulated platelets fail to bind fibrinogen, and binding was minimal in the stages of activation immediately following adhesion. The amount of fibrinogen bound per platelet increased rapidly during the shape changes associated with surface activation until 7,600 +/- 500 labels were present at saturation. Maximal binding of fibrinogen was followed by receptor redistribution. During the early stages of spreading, fibrinogen labels were uniformly distributed over the entire platelet surface, including pseudopodia, but the labels become progressively centralized as the spreading process continued. In well spread platelets, labels were found over the central regions, whereas peripheral areas were cleared of receptors. Receptor redistribution during spreading was accompanied by cytoskeletal reorganization such that a direct correlation was seen between the development of specific ultrastructural zones and the distribution of surface receptor sites suggesting a link between the surface receptors and the cytoskeleton. The association of fibrinogen receptors with contractile elements of the cytoskeleton, which permits coordinated receptor centralization, is important to the understanding of the role of fibrinogen in normal platelet aggregation and clot retraction.

Platelet activation and cytoskeletal reorganization: high voltage electron microscopic examination of intact and Triton-extracted whole mounts

The sequential changes in the three-dimensional organization of the filamentous components of human platelets following surface activation were investigated in whole-mount preparations. Examination of intact and Triton-extracted platelets by high voltage electron microscopy provides morphological evidence of increased polymerization of actin into the filamentous form and an increased organization of the cytoskeletal elements after activation. The structure of resting platelets consists of the circumferential band of microtubules and a small number of microfilaments randomly arranged throughout a dense cytoplasmic matrix. Increased spreading is accompanied by cytoskeletal reorganization resulting in the development of distinct ultrastructural zones including the peripheral web, the outer filamentous zone, the "trabecular-like" inner filamentous zone, and the granulomere . These zones are present only in well-spread platelets during the late stages of surface activation and are retained following Triton extraction. Extraction of the less stable cytoplasmic components provides additional information about the underlying structure and filament interactions within each zone.

Inhibition of platelet shape-change by sodium thiamylal

Canine platelets were treated in vitro with sodium thiamylal and allowed to surface activate on glass coverslips. Platelet surface activation was markedly inhibited by sodium thiamylal at concentrations as low as 2 X 10(-4) M and this inhibitory effect was most pronounced after pretreating the platelets for 30 minutes with sodium thiamylal. Treatment with sodium thiamylal prevented spreading platelets from reaching the fully spread stage. Additional experiments demonstrated that sodium thiamylal need not be present in the medium during the activation process in order to exert its effect. Preliminary platelet aggregation studies show sodium thiamylal in the 10(-4) - 10(-3) M range to be capable of inhibiting aggregation induced by adenosine diphosphate.

The effect of the dimeric and multimeric forms of fibronectin on the adhesion and growth of primary glomerular cells

Primary glomerular cells placed in a chemically defined medium containing Waymouth's medium MB 752/1 supplemented with insulin, transferrin, fibroblast growth factor, nonessential amino acids, sodium pyruvate, and antibiotics showed rapid outgrowth of cells which morphologically resembled well differentiated visceral epithelial cells followed by outgrowth of poorly differentiated cells; morphologic evidence suggests these latter cells are precursor cells of the epithelial cell lineage. Whereas the well differentiated glomerular epithelial cells were never observed to divide by sequential phase microscopic observations, a chemically defined medium was developed for optimal growth of the poorly differentiated cell type. This serum-free medium contained Waymouth's medium MB 752/1 supplemented with insulin, transferrin, selenium, and fibronectin (plus non-essential amino acids, sodium pyruvate, and antibiotics). Using this chemically defined medium, we have compared the effects of dimeric and multimeric fibronectin (high molecular weight disulfide-bonded fibronectin produced by incubation of dimeric fibronectin with 3 M guanidine followed by dialysis against 0.05 M cyclohexylaminopropane sulfonic acid (CAPS) buffer, pH 11) on the adhesion and growth of the poorly differentiated primary glomerular cell type. Dimeric fibronectin (FN) was twice as effective as multimeric FN in promoting glomerular cell adhesion, although both forms of FN promoted cell adhesion better than an uncoated substratum. In contrast, cell growth studies demonstrated that multimeric FN was a more potent growth stimulant than dimeric FN. The differential effects of dimeric and multimeric forms of FN in vitro suggests that these molecules may have different functions in vivo.

A morphologic and immunofluorescent analysis of primary guinea pig glomerular cell types grown in chemically defined media. Evidence for clonal growth and cell differentiation

Primary kidney guinea pig glomerular cells were successfully grown in chemically defined media containing insulin, transferrin, and fibronectin or glycylhistidyllysine and fibronectin. Morphologic analysis of glomerular cells grown in either of these chemically defined media provided identical results with respect to cell growth properties and cell types involved. Electron microscopic studies of glomeruli early after they had been placed in culture showed definite evidence of "dedifferentiation" of some glomerular cells. Most glomerular cells in later cultures were undifferentiated. However, since electron microscopic analyses of glomeruli in confluent cultures demonstrated that the majority of cells in culture grow from the epithelial side of the glomerular basement membrane, we suggest that these cells were some form of epithelial cell. This conclusion was further strengthened by the fact that cells resembling well differentiated glomerular epithelial cells were seen in cultures of glomeruli grown in chemically defined media; these cells have never been observed in glomeruli grown in calf serum. Fluorescent microscopy of cell stained with the mitochondrial stain rhodamine 123 allowed identification of several glomerular cell types according to distribution, number, and morphology of mitochondria. Similarly, indirect immunofluorescent microscopy studies using antibodies to fibronectin or laminin provided evidence that glomerular cells separated into cell types according to mitochondrial staining properties were unique biochemically. Using these histochemical criteria it was possible to demonstrate that certain of the glomerular cell types could be selectively grown by addition of the enzyme galactose oxidase to the media. Analysis of our morphologic and histochemical results suggests the possibility that clonal growth and differentiation of glomerular epithelial cells occurs when glomeruli are placed in chemically defined media, and our results are compatible with the hypothesis that either "stem cells" or "dedifferentiated" cells are the primary cells dividing in culture.

Scanning electron microscopy after cytologic examination of urinary cells: lack of diagnostic advantage using combined microscopy

A simple method for combined light microscopy (LM) and scanning electron microscopy (SEM) of urinary sediment is described. Spontaneously voided cells were routinely collected onto a filter for cytologic study. Individual cells were photographed and demarcated by an ink grid pattern and puncture marks in the filter. The filter was prepared for SEM. The cells that were studied by LM could be readily located and examined by SEM. This study showed the importance of identifying individual cells before observation by SEM since cells with similar appearances by LM may have markedly different features by SEM, and vice versa. The results obtained in a series of patients with transitional-cell bladder carcinoma indicate that degenerative changes in voided urothelial cells negate the utility of SEM as a routine screening tool.

Blood clearance tests for detecting 2,3,7,8-tetrachlorodibenzo-p-dioxin hepatotoxicity in rats and rabbits

The objective was to determine if a blood clearance test would detect liver dysfunction in rats and rabbits treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Guinea pigs were included as a negative control, because TCDD does not produce detectable hepatotoxicity in this species. TCDD was given as a single dose to male rats (25 microgram/kg, po), rabbits (25 microgram/kg, ip) and guinea pigs (2 microgram/kg, ip) and liver function was assessed 10 days later by determining blood clearance of indocyanine green (ICG) and ouabain. Activity in serum of sorbitol dehydrogenase (SDH), glutamic pyruvic transaminase (SGPT) and gamma glutamyl transpeptidase (gamma GTP) were also measured and light microscopy performed on the liver. The results showed that hepatotoxicity in the rabbit could be detected by a reduction in ICG blood clearance and an elevation in SDH activity. In the rat, ouabain blood clearance was reduced and SDH activity elevated. None of the liver function tests were altered in the guinea pig. These results underline the usefulness of blood clearance tests using ICG and ouabain in detecting TCDD hepatotoxicity in animals.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on indocyanine green blood clearance in rhesus monkeys

To assess effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on liver function adult male rhesus monkeys were treated with a single oral dose of acetone/corn oil (control) or 5, 25, or 75 micrograms/kg TCDD. Each monkey was used as its own control and indocyanine green (ICG) blood clearance and the following serum enzymes: glutamic pyruvate transaminase (SGPT), sorbitol dehydrogenase (SDH) and gamma glutamyl transpeptidase (gamma GTP), were measured at regular intervals for 4 weeks before and 17 weeks after treatment. In control monkeys ICG blood clearance and serum enzymes were similar before and after treatment. However, in the monkey that received 5 micrograms/kg TCDD there was a mild increase in ICG blood clearance followed by a slight decrease. The magnitude of this biphasic change was greater in monkeys that received 25 and 75 micrograms/kg TCDD and the decrease in clearance was invariably associated with a 1--2-week period before the monkeys died. SDH and SGPT activities were elevated at some time during the course of intoxication in all TCDD-treated monkeys but gamma GTP activity was not altered. The monkey treated with 5 micrograms/kg TCDD survived but monkeys treated with 25 and 75 micrograms/kg died 4--6 weeks after treatment. Light microscopy of the livers of TCDD-treated monkeys that died revealed fatty infiltration with minimal hepatocellular necrosis.

Murine macrophage-lymphocyte interactions: scanning electron microscopic study

Light and scanning electron microscopic observations revealed murine macrophage-lymphocyte interactions involving the initial contact of peritoneal, spleen, or thymus lymphocytes with peritoneal macrophage processes or microprocesses followed by clustering of lymphocytes over the central nuclear area of the macrophages. Lymphocyte-lymphocyte clustering was not observed in the absence of macrophages. Attachment and subsequent clustering appeared not to require the presence of serum or antigen; the attachment of allogeneic or xenogeneic lymphocytes was comparable to that seen in the syngeneic system, but central clustering of these lymphocytes failed to occur. No attachment or clustering was observed when thymic lymphocytes were cultured with thymus derived fibroblasts rather than with peritoneal macrophages. Lymphocyte attachment to immune, antigen-activated, syngeneic macrophages occurred more rapidly than that to normal unstimulated syngeneic macrophages; however, lymphocytes attached to the "activated" macrophages appeared to be killed by a nonphagocytic mechanism. A similar increase in the rate of lymphocyte attachment to macrophages occurred in the presence of migration inhibitory factor. Subsequent lymphocyte clustering on macrophages was observed in the migration inhibitory factor-stimulated cultures. In addition, lymphocyte-macrophage interactions similar to those in vitro were observed to occur in vivo on intraperitoneally implanted cover slips.