Brazilian consensus on Helicobacter pylori and associated diseases

Non-granulomatous nodular accumulations of inflammatory cells in inflammatory myopathies were studied to characterize adhesion mechanisms used for leukocyte recruitment. The nodules had a B-cell-rich center surrounded by a helper T-cell-rich peripheral zone, resembling lymph nodes. The T-cell-rich zones harbored high-walled venules resembling high endothelial venules (HEV), whose endothelia frequently expressed ICAM-1, VCAM-1, and less constantly E-selectin. This endothelial adhesion molecule profile differs from that found in polymyositis, inclusion body myositis, or dermatomyositis, but resembles that in lymphoid tissues. Also, the peripheral lymph node addressin, a vascular addressin specific for peripheral lymphoid tissue HEV, was present on many HEV. This adhesion system is probably responsible for the excessive lymphocyte recruitment. The similar cellular organization and lymphocyte recirculation mechanisms of the nodular infiltrates in muscle and of lymph nodes suggest that the former may also produce antibodies.     

Reduced phagocytosis of apoptotic cells in malignant lymphoma

Efficient removal of lymphocytes undergoing programmed cell death (apoptosis) by macrophages plays an important role for the proper function of normal immune system. Furthermore, in malignant lymphoma, elimination of apoptotic tumor cells by phagocytes contributes to the anti-tumor immune response. It is unknown, however, whether macrophages in normal and malignant lymphoid tissues differ in their ability to recognize and remove apoptotic cells. Our present results demonstrate that normal and malignant lymphoid tissues differ according to the extent of the infiltration by macrophages. The highest densities of macrophages (p < 0.0001) were detected in diffuse large B-cell lymphoma, centroblastic (DLBCL-CB) and immunoblastic variants and Burkitt's lymphoma. The grade of the macrophage infiltration correlated with the proliferation rates of the tumors (p < 0.0001). Compared with normal lymphoid organs, malignant lymphoma contained lower percentages of apoptotic cells phagocytosed by tissue macrophages (p < 0.001). Of all lymphomas tested, mantle cell lymphoma and DLBCL-CB expressed the lowest percentages of phagocytosed apoptotic cells (p < 0.0001).     

Vascular adhesion protein 1 (VAP-1) mediates lymphocyte subtype-specific, selectin-independent recognition of vascular endothelium in human lymph nodes

Interactions between lymphocyte surface receptors and their ligands on vascular endothelial cells regulate the exit of lymphocytes from the circulation. Distinct subsets of mononuclear cells bind to high endothelial venules (HEVs) in different lymphoid organs to a different extent, but the molecular mechanisms behind this selectivity have remained poorly characterized. Here we show that vascular adhesion protein-1 (VAP-1) mediates subtype-specific binding of CD8-positive T cells and natural killer cells to human endothelium. VAP-1-dependent, oligosaccharide-dependent peripheral lymph node (PLN) HEV adhesion under shear was independent of L-selectin, P-selectin glycoprotein ligand 1, and alpha4 integrins, the known lymphocyte receptors involved in the initial recognition of endothelial cells. PLN HEV adhesion was also critically dependent on peripheral lymph node vascular addressins (PNAds), but lymphocyte L-selectin was absolutely required for PNAd binding. Most lymphocytes relied on both PNAd and VAP-1 in HEV binding. The overlapping function of L-selectin ligands and VAP-1 in PLN introduces a new control point into the lymphocyte extravasation process. Finally, intravital microscopy revealed that VAP-1 is involved in initial interactions between human lymphocytes and endothelial cells in inflamed rabbit mesenterial venules in vivo. In conclusion, VAP-1 is a novel contact-initiating ligand that discriminates between different subpopulations of mononuclear cells and is an appealing target for selective modulation of adhesion of CD8- and CD16-positive effector cells.     

Characterization of a novel subset of T cells from human spleen that lacks L-selectin

Human L-selection (LAM-1, Leu-8, TQ1, DREG 56) is a member of the 'selection' family of adhesion molecules. Antibodies to L-selectin have been shown to block the binding of T cells to peripheral lymph node high endothelial venules (HEV). Most unstimulated peripheral blood T cells express high levels of L-selectin whilst it is only weakly expressed on the majority of T cells from secondary lymphoid organs. We show here (a) that T cells from tonsil and lymph node up-regulate L-selectin when released from their microenvironment, (b) that in contrast, spleen contains a stable L-selectin negative subset, (c) that this subset remains surface L-selection negative after stimulation even though the T cells can respond by proliferation, (d) that this subset expresses minimal levels of LAM-1 mRNA and (e) that mucosal lymphocyte antigen (MLA) positive and T-cell receptor (TcR) gamma delta positive T cells found within the L-selectin negative population are similar to subsets of T cells found amongst lamina propria (LP) and intraepithelial lymphocytes (IEL) of the gut.     

In situ analysis of lymphocyte migration to lymph nodes

Blood-borne lymphocytes migrate continuously to peripheral lymph nodes (PLN) and other organized lymphoid tissues where they are most likely to encounter their cognate antigen. Lymphocyte homing to PLN is a highly regulated process that occurs exclusively in specialized high endothelial venules (HEV) in the nodal paracortex. Recently, it has become possible to explore this vital aspect of peripheral immune surveillance by intravital microscopy of the subiliac lymph node microcirculation in anesthetized mice. This paper reviews technical and experimental aspects of the new model and summarizes recent advances in our understanding of the molecular mechanisms of lymphocyte homing to PLN which were derived from its use. Both lymphocytes and granulocytes initiate rolling interactions via L-selectin binding to the peripheral node addressin (PNAd) in PLN HEV. Subsequently, a G protein-coupled chemoattractant stimulus activates LFA-1 on rolling lymphocytes, but not on granulocytes. Thus, granulocytes continue to roll through the PLN, whereas LFA-1 activation allows lymphocytes to arrest and emigrate into the extravascular compartment. We have also identified a second homing pathway that allows L-selectin low/(activated/memory) lymphocytes to home to PLN. P-selectin on circulating activated platelets can mediate simultaneous platelet adhesion to PNAd in HEV and to P-selectin glycoprotein ligand (PSGL)-1 on lymphocytes. Through this mechanism, platelets can form a cellular bridge which can effectively substitute for the loss of L-selectin on memory cell subsets.     

A high endothelial cell-derived chemokine induces rapid, efficient, and subset-selective arrest of rolling T lymphocytes on a reconstituted endothelial substrate

The homing of lymphocytes to secondary lymphoid organs is thought to involve the action of chemokines. Secondary lymphoid-tissue chemokine (SLC), a high endothelial venule (HEV)-associated chemokine, has emerged as a candidate for participating in this process. We now show that immobilized SLC strongly induces beta2 integrin-mediated binding of T lymphocytes of naive phenotype and B lymphocytes to ICAM-1 under static conditions. This effect is not mediated by beta2 integrin affinity modulation, because SLC does not elicit a beta2 integrin activation epitope (mAb24) on naive T lymphocytes. In a parallel plate flow chamber, lymphocytes rolling via L-selectin are rapidly arrested through beta2 integrins in a pertussis toxin-sensitive manner on a substrate consisting of L-selectin ligands (peripheral lymph node addressins) together with ICAM-1 and SLC. Naive T lymphocytes are arrested on the HEV substrate with sixfold higher efficiency than memory cells. Neutrophils roll, but are not arrested by SLC, whereas they respond to immobilized IL-8 with rapid arrest. Thus, our artificial HEV system recapitulates critical features of lymphocyte interactions with HEV in vivo. These observations strongly point to the participation of SLC in homing of lymphocytes to secondary lymphoid organs.     

Efficient lymphocyte migration across high endothelial venules of mouse Peyer's patches requires overlapping expression of L-selectin and beta7 integrin

Lymphocyte migration into lymphoid organs is regulated by adhesion molecules including L-selectin and the beta7 integrins. L-selectin and alpha4beta7 are predominantly hypothesized to direct the selective migration of lymphocytes to peripheral lymph nodes and the gut-associated lymphoid tissues, respectively. To further characterize interactions between L-selectin and beta7 integrins during lymphocyte recirculation, mice deficient in both receptors (L-selectin/beta7 integrin-/-) were generated. The simultaneous loss of L-selectin and beta7 integrin expression prevented the majority of lymphocytes (>95% inhibition) from attaching to high endothelial venules (HEV) of Peyer's patches and other lymphoid tissues during in vitro binding assays. Moreover, the inability to bind HEV eliminated the vast majority of L-selectin/beta7 integrin-/- lymphocyte migration into Peyer's patches during short-term and long-term in vivo migration assays (>99% inhibition,p < 0.01). The lack of lymphocyte migration into Peyer's patches correlated directly with the dramatically reduced size and cellularity (99% reduced) of this tissue in L-selectin/beta7 integrin-/- mice. High numbers of injected L-selectin/beta7 integrin-/- lymphocytes remaining in the blood of wild-type mice correlated with markedly increased numbers of circulating lymphocytes in L-selectin/beta7 integrin-/- mice. Loss of either L-selectin or the beta7 integrins alone resulted in significant but incomplete inhibition of Peyer's patch migration. Collectively, the phenotype of L-selectin/beta7 integrin-/- mice demonstrates that these two receptors primarily interact along the same adhesion pathway that is required for the vast majority of lymphocyte migration into Peyer's patches.     

Impaired phagocytosis of apoptotic cell material by monocyte-derived macrophages from patients with systemic lupus erythematosus

OBJECTIVE: To investigate whether the established impaired phagocyte function in systemic lupus erythematosus (SLE) patients also affects apoptotic cell clearance. Accumulation of apoptotic waste as a source for autoantigens that induce and maintain autoimmune responses is discussed. METHODS: Apoptosis was detected by morphology and propidium iodide staining. In vitro phagocytosis of autologous apoptotic cells in cultured peripheral blood mononuclear cells was evaluated microscopically. Cross-feeding experiments were performed to investigate phagocytosis of heterologous apoptotic cells by in vitro-differentiated macrophages. Furthermore, the effect of annexin V on the phagocytosis of apoptotic cells was investigated. RESULTS: Reduced clearance of apoptotic cells in SLE patients was observed. The defective clearance appeared to reflect phagocyte dysfunction and not an abnormal execution of apoptosis. A similar picture was seen when in vitro-differentiated macrophages from control populations were treated with annexin V. CONCLUSION: Noninflammatory engulfment phagocytosis of apoptotic cells is decreased in SLE patients. Persistently circulating apoptotic waste may encounter inflammatory removal pathways and serve as immunogen for the induction of autoreactive lymphocytes and as antigen for immune complex formation.     

Nucleosomes inhibit phagocytosis of apoptotic thymocytes by peritoneal macrophages from MRL+/+ lupus-prone mice

The nucleosome, the basic structure of chromatin and normal product of cell apoptosis, plays a pivotal role both in the induction and the pathogenesis of systemic lupus erythematosus (SLE). Nucleosomes have been found to circulate at high levels in patients with SLE and apoptosis of lymphoid cells is increased during human and murine lupus. In this study, we examined the presence of possible defects in clearance mechanisms of apoptotic cells in murine lupus, and questioned further whether nucleosomes could compromise this phagocytic process. There did not appear to be any intrinsic functional defect of macrophages from young MRL+/+ lupus-prone mice to recognize and phagocytose apoptotic thymocytes. Nucleosomes, as a mimic of increased cell apoptotsis in vivo, induced a strong, dose-dependent, inhibition of phagocytosis of apoptotic thymocytes by young, pre-autoimmune, macrophages of MRL+/+ mice, whereas macrophages of non-autoimmune C3H mice only exhibited a trend to inhibition. The nucleosome-elicited inhibitory effect persisted during the development of the autoimmune response and appeared to be specific for the molecular mechanisms involved in macrophage phagocytosis of apoptotic cells. Our data suggest that nucleosome elicited inhibition of phagocytosis of apoptotic cells by MRL+/+ macrophages before the onset of the autoimmune response contribute, in a positive loop, to sustain and/or augment the levels of circulating (and potentially immunogenic) nucleosomes in lupus.     

Fever-range hyperthermia enhances L-selectin-dependent adhesion of lymphocytes to vascular endothelium

The L-selectin leukocyte adhesion molecule plays an important role in controlling leukocyte extravasation in peripheral lymph nodes and at sites of tissue injury or infection. Although febrile responses during infection and inflammation are associated with enhanced immune activity, the contribution of fever-range temperatures to controlling lymphocyte recruitment to tissues has not been previously examined. In this report we provide evidence that direct exposure of lymphocytes to fever-range temperatures (38-41 degrees C) in vitro for 9 to 24 h resulted in a >100% increase in L-selectin-dependent adhesion of these cells to lymph node high endothelial venules (HEV). Moreover, culture of lymphocytes under hyperthermia conditions markedly enhanced the ability of these cells to traffic in an L-selectin-dependent manner to peripheral lymph nodes, mesenteric lymph nodes, and Peyer's patches. In contrast, febrile temperatures did not increase LFA-1 function as assessed by measuring lymphocyte adhesion to ICAM-1-3T3 transfectants. Fever-range hyperthermia further did not increase L-selectin surface density on lymphocytes or L-selectin-dependent recognition of soluble carbohydrate substrates; however, a marked increase in ultrastructural immunogold-labeling of L-selectin was observed in response to thermal stimuli. These results suggest that elevated temperatures enhance L-selectin adhesion and/or avidity through the regulation of L-selectin conformation or organization in the plasma membrane. Finally, the observed thermal effects on L-selectin adhesion were attributed to soluble factors in the conditioned medium of heat-treated cells. Taken together, these data provide new insight into the potential physiologic role of the febrile response in enhancing lymphocyte recruitment to tissues through the regulation of L-selectin adhesion.     

Lymphocyte emigration from high endothelial venules in rat lymph nodes

Sequential events during lymphocyte emigration from high endothelial venuses (HEV) were studied by scanning and transmission electron microscopy combined with regional perfusion techniques. The results indicate that blood lymphocytes selectively adhere to HEV surfaces through microvilli which attach to shallow pits on the luminal surfaces of high endothelial cells. These intercellular contact points resist hydrodynamic and osmotic shearing forces, but can be disrupted by treatments which remove endothelial glycocalyx, hydrolyse lymphocyte surface glycoproteins, or chelate divalent cations. After this initial attachment phase, lymphocytes enter apical clefts between endothelial cells where they assume a motile configuration characterized by loss of microvilli and formation of irregular surface folds. Intramural lymphocytes adhere to adjacent endothelial cells through macular and villous contacts. Fibrillar electron-dense material traverses the 15-20 nm gap at these points of adhesion. Microtubules and microfilaments are also seen around areas of cytoplasmic constriction in these motile lymphocytes. The migrating lymphocytes show cytoplasmic polarity which is oriented in the direction of movement as they pass through extracellular spaces in the venular wall and cross successive laminations in the perivascular sheath to enter the node. Since these lymphocytes enter channels between endothelial cells which are stained by intralymphatic injections with horseradish peroxidase, it is suggested that their entry into the node depends upon migration along a chemotactic gradient.     

Apoptosis induced in vivo during acute infection by porcine reproductive and respiratory syndrome virus

We studied apoptosis caused by porcine reproductive and respiratory syndrome virus (PRRSV) in vivo, focusing on the tissues that constitute the main targets for infection: lung and lymphoid tissues. Previous investigators have shown that the PRRSV glycoprotein p25, encoded by PRRSV open reading frame 5, induces apoptosis when expressed in COS-1 cells. Results of studies conducted in our laboratory indicate the simultaneous occurrence of PRRSV-induced alterations of spermatogenesis and apoptotic death of germinal epithelial cells in the testicle. In this study, the goal was to determine whether virus-induced apoptosis is a direct mechanism of cell death caused by PRRSV in infected pigs. Eight 3-week-old pigs were intranasally inoculated with PRRSV 16244B, a highly virulent field strain. Lung, tonsil, bronchial lymph node, spleen, and heart were assessed histologically at 4 and 7 days postinfection. To characterize PRRSV-infected cells and apoptotic cell death, we used immunohistochemical methods for detection of viral antigen, DNA electrophoresis for detection of DNA fragmentation, the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-fluorescein nick end labeling method for in situ detection of DNA strand breaks, and electron microscopy for ultrastructural morphologic studies. PRRSV infection resulted in widespread apoptosis in the lungs and lymphoid tissues of infected pigs. Virus infection-induced apoptotic cells were more abundant than PRRSV-infected cells in all tissues. DNA laddering was detected in lung and lymphoid tissues. However, double-labeling experiments demonstrated that the majority of apoptotic cells did not colocalize with PRRSV-infected cells. Our findings suggest the presence of an indirect mechanism in the induction of apoptosis for PRRSV.     

Mucosal addressin is required for the development of diabetes in nonobese diabetic mice

Immune responses are best initiated in the environment of lymphoid tissues wherein circulating lymphocytes enter by interacting with endothelial adhesion molecules. In type 1 diabetes, immune responses against pancreatic islets develop, but the environment in which this occurs remains unidentified. To determine whether lymphocyte homing to lymphoid organs is involved in the pathogenesis of diabetes in nonobese diabetic (NOD) mice, we blocked the function of the mucosal addressin cell adhesion molecule-1 (MAdCAM-1), which is a vascular addressin-mediating lymphocyte homing into mucosal lymphoid tissues, in these mice. While ineffective if started later, a blockade started at 3 wk of age reduced the incidence of diabetes from 50% to 9% (p < 0.01). This finding is associated with Peyer's patch atrophy, a marked decrease of naive (CD44(low) CD45RB(high)) T lymphocytes, and a reduction in the relative numbers of memory (CD44(high)) T lymphocytes in the spleen. The potential of these spleen cells to cause diabetes was diminished. Anti-MAdCAM-1 treatment also inhibited both lymphocyte entry into the pancreas and diabetes development in NOD/SCID recipients after the transfer of lymphocytes derived from the mesenteric lymph nodes of young, but not of diabetic, NOD donors. Therefore, MAdCAM-1 may be required during two distinct steps in an early phase of diabetes development: for the entry of naive lymphocytes into the lymphoid tissues in which diabetes-causing lymphocytes are originally primed, and for the subsequent homing of these lymphocytes into the pancreas. The role of MAdCAM-1 as a mucosal vascular addressin suggests that mucosal lymphoid tissues are involved in the initiation of pathologic immune responses in NOD mice.     

Expression and regulation of the porcine CD44 molecule

The expression and regulation of porcine CD44 were studied under various experimental conditions and in the context of lymphocyte differentiational and functional status. The CD44 molecule was subject to antigenic modulation by the anti-CD44 mAbs to different degrees depending on the type of cross-linking reagent and could be induced to shed from the cell surface. The reexpression of CD44 on papain-denuded lymphocytes was heterogeneous, as about half of the cells failed to resynthesize the molecule after prolonged culture, whereas the rest of the cells had a high turnover. Stimulation of lymphocytes by mitogens caused prolonged, dose-dependent elevation of the expression of CD44. Expression of CD44 on lymph node cells was found to be correlated with the expression of CD2 and sIgM. A CD2-CD4-sIgM-CD44-MHC Class IIhiCD45+ cell subset was identified, which was present in small numbers in lymph nodes but was enriched in gut-associated lymphoid tissues. In the thymus, CD44 expression seemed to be correlated with the differentiation status of thymocytes. In general, the expression of CD44 in the lymphoid tissues tested appeared to be related to their level of cell migration capacity.     

Production of proinflammatory cytokines by phorbol myristate acetate-treated THP-1 cells and monocyte-derived macrophages after phagocytosis of apoptotic CTLL-2 cells

Because it is generally believed that apoptosis is not associated with inflammation, we hypothesized that the interaction of phagocytes with apoptotic cells provides a negative or null signal for inflammation. However, we recently found that the interaction led to the production of proinflammatory cytokines but not antiinflammatory cytokines, although the apoptotic cell membranes appeared to be intact. In this study, we examined in detail the relationship among the kinetics of apoptosis, phagocytosis and production of cytokines by macrophages. Among the time points examined, murine CTLL-2 cells became apoptotic in terms of cell size and exposure of phosphatidylserine after 12 h of culture in the absence of IL-2, and at the same time they began to be phagocytosed and lead to proinflammatory cytokine production by PMA-treated THP-1 cells (human macrophages). The phagocytosis of apoptotic cells by macrophages was also confirmed by confocal laser microscopy. The coculturing of human macrophages with murine apoptotic cells led to the production of human proinflammatory cytokines, notably IL-8, at both the mRNA level and the protein level. The coculturing of monocyte-derived macrophages with the apoptotic cells also led to the production of IL-8 protein. Both the phagocytosis and production of the cytokines were suppressed by either phospho-L-serine or RGDS (Arg-Gly-Asp-Ser), but not by RGES (Arg-Gly-Glu-Ser). Thus, the production of proinflammatory cytokines and phagocytosis of apoptotic CTLL-2 cells appear to be closely interrelated.     

Catecholamine modulation of lymphocyte homing to lymphoid tissues

Lymphocyte migration is an essential process for immune surveillance and for promoting cell-cell interactions necessary to generate an immune response. This report examined whether catecholamine prestimulation would alter the pattern of lymphocyte homing to spleen and lymph nodes in mice as determined by tracking fluorescently labeled cells. The results of cell sorter analysis showed that catecholamine-pretreated cells had increased accumulation in spleen and lymph nodes 1 and 2 h after i.v. injection. In addition, microscopic analysis showed that labeled cells migrated from the splenic red pulp to T-cell regions of the white pulp over a 2-h time course. Within the lymph nodes, labeled cells localized predominantly to the pericortex. Additional studies examined the migration of lymphocytes to lymphoid tissues of NGF-transgenic mice that have sympathetic hyperinnervation of spleen and peripheral lymph nodes. In contrast to the studies above, migration of T-cells from control mice to lymphoid tissues of the hyperinnervated mice was not different than that in control mice in most tissues. The accumulation of lymphocytes in lymphoid tissues is a balance between the influx of newly migrated cells and efflux back into the circulation. The studies in this report lend support to other studies showing catecholamine modulation of lymphocyte migration and homing, but it is a complex process about which much has yet to be understood.     

Direct-exchange arthroplasty for the treatment of infection after total hip replacement. An average ten-year follow-up

The recirculation of naive lymphocytes from blood to lymph that is initiated in high endothelial venules (HEV) of secondary lymphoid organs such as lymph nodes and Peyer's patches (PP) is regulated by multiple interactions of adhesion receptor/counter-receptor pairs involving both selectins and integrins. We showed previously that blocking of only L-selectin is sufficient to ablate trafficking of naive CD4 cells and the development of their responses in peripheral lymph nodes but not in PP where alpha4beta7 integrins are thought to primarily regulate entry. However, although antibody to alpha4 integrins partially inhibited homing of naive CD4 cells to PP and not to lymph nodes, there was no effect on the development primary responses in these tissues or spleens. Since previous studies indicate that both alpha4beta7 integrins and L-selectin regulate adhesion of naive cells to PP HEV, we examined the effect a blockade of both adhesion pathways on the recirculation of naive CD4 cells. There was no detectable homing of naive CD4 cells to PP or lymph nodes when interactions with both receptors were inhibited, resulting in a profound depletion of naive CD4 cells and loss of antigen responses in these sites. In contrast, increased numbers of naive CD4 cells and responses of higher magnitude were found in the spleen. The results demonstrate recirculation of naive CD4 cells through tissues where entry is controlled through HEV is essential for the local generation of primary responses.     

Human mucosal addressin cell adhesion molecule-1 (MAdCAM-1) demonstrates structural and functional similarities to the alpha 4 beta 7-integrin binding domains of murine MAdCAM-1, but extreme divergence of mucin-like sequences

The mucosal vascular addressin, mucosal addressin cell adhesion molecule-1 (MAdCAM-1), is an Ig family adhesion receptor preferentially expressed by venular endothelial cells at sites of lymphocyte extravasation in murine mucosal lymphoid tissues and lamina propria. MAdCAM-1 specifically binds both human and mouse lymphocytes that express the homing receptor for Peyer's patches, the integrin alpha 4 beta 7. Functional expression cloning was used to isolate a cDNA from a macaque mesenteric lymph node library that encodes the homologue to murine MAdCAM-1. The macaque cDNA was subsequently used to clone the human homologue as well. Expression of human MAdCAM-1 RNA is restricted to mucosal tissues, gut-associated lymphoid tissues and spleen. Human MAdCAM-1 selectively binds both murine and human lymphocyte cell lines expressing alpha 4 beta 7. Human and macaque MAdCAM-1 have two Ig-like domains that are similar to the two amino-terminal integrin binding domains of murine MAdCAM-1. The conservation of sequences within the region homologous to the mucin/IgA domain of murine MAdCAM-1 is, however, much less apparent. These receptors exhibit considerable variation from murine MAdCAM-1 with respect to the length of the mucin-like sequence and the lack of a membrane proximal Ig (IgA-like) domain. The isolation of these different species of MAdCAM-1 demonstrates greater seleoffctive pressure for maintenance of amino acids involved in alpha 4 beta 7 binding than those sequences presumably involved in the presentation of carbohydrates for selectin binding.     

Endothelial cell-binding properties of lymphocytes infiltrated into human diabetic pancreas. Implications for pathogenesis of IDDM

In IDDM, mononuclear cells accumulate in the islets of Langerhans and destroy insulin-producing beta-cells. To study the mechanisms that control extravasation of circulating mononuclear cells into the pancreas, we examined the phenotype of vascular endothelium of the pancreas, propagated a T-cell line from pancreatic islets at the onset of the disease and compared endothelial binding of this cell line in vitro to vascular endothelium in different body regions. The adhesion molecules expressed on the resulting T-cell line and the functional binding capacity of these cells to the endothelium of the normal and diabetic pancreas, mucosa-associated lymphatic tissues, and regional and peripheral lymph nodes were studied. We present evidence of pancreatic endothelial activation in diabetes, leading to endothelial morphology typical for HEVs and accompanying local increase in extravasation of mononuclear cells into the pancreas. Endothelial-cell binding experiments with the T-cell line showed strong adherence of the cells to the endothelium of diabetic pancreas and mucosal lymphoid tissue. The cell line was uniformly CD4-positive, TCR V beta 5.1-positive, LFA-1-positive (CD 11a/CD18), VLA-4 alpha-positive (CD 49d), and CD 44-positive but negative for L-selectin (peripheral lymph node homing receptor). The pancreatic or control cell lines showed no binding to vessels of normal pancreas, and the binding of the pancreatic cell line to the endothelium of peripheral lymph node was weak. Our results suggest that lymphocyte-endothelial cell interactions are important for the accumulation of inflammatory mononuclear cells into the pancreas and imply that lymphocytes derived from the mucosal lymphoid tissue may be involved in the pathogenesis of IDDM.     

Essential role of phosphatidylserine externalization in apoptosing cell phagocytosis by macrophages

In many apoptotic cells, phosphatidylserine (PS), that is normally restricted to the inner membrane layer, is externalized and subsequently recognized by phagocytes. However, it has been unclear whether PS externalization is sufficient for phagocytosis induction. In a cultured cell line undergoing Fas-mediated apoptosis, PS externalization preceded other apoptotic events. When transbilayer movement of membrane phospholipids was analyzed, a decrease of the uptake of PS and phosphatidylethanolamine and an increase of phosphatidylcholine incorporation were observed upon apoptosis induction. Apoptotic cultured cells were phagocytosed by macrophages in a manner dependent on externalized PS before plasma membrane permeability increased. Moreover, a N-ethylmaleimide treatment caused PS externalization independent of apoptosis, and such cells underwent PS-mediated phagocytosis. These results suggested that PS is externalized as a result of membrane phospholipid redistribution and externalized PS by itself induces apoptosing cell phagocytosis.