L-selectin is not essential for naive CD4 cell trafficking or development of primary responses in Peyer's patches

We showed previously that L-selectin-dependent recirculation of naive CD4 cells is essential for development of primary responses in peripheral lymph nodes. Recent studies suggest that L-selectin is also required for lymphocyte entry into gut mucosal lymphoid tissues that include Peyer's patches and mesenteric lymph nodes. Here we show that anti-L-selectin antibody, MEL-14, inhibited homing of a rigorously purified, homogenous population of naive CD4 cells into both of these tissues as well as peripheral lymph nodes, directly demonstrating a role for this receptor in regulating entry into gut-associated sites. However, in intact animals, treatment with MEL-14 resulted in the loss of naive CD4 cells (CD45RB^hi, CD44^lo) from peripheral lymph nodes but not Peyer's patches, whereas mesenteric lymph nodes were intermediate in this regard. In mice primed by parenteral immunization with keyhole limpet hemocyanin (KLH), primary CD4 responses were readily detected in both Peyer's patches and mesenteric lymph nodes, and were not affected by exposure to MEL-14. Indeed, similar frequencies of KLH-specific CD4 cells were recovered from both of these tissues irrespective of MEL-14 treatment. The results indicate that interactions with L-selectin can be circumvented to allow entry of naive CD4 cells into Peyer's patches but not peripheral lymph nodes.     

The migratory behavior of murine CD4+ cells of memory phenotype

Lymphocyte differentiation is connected with profound alterations in the migratory pattern of lymphocytes. Whereas naive cells predominantly recirculate through lymphoid tissues, activated lymphocytes acquire an increased preference for immigration into non-lymphoid tissues and a reduced capacity for recirculation via high endothelial venules (HEV). A variety of data had indicated that memory-related subpopulations of cells in man and sheep, classified by the low expression of the CD45RA isotype, also lack the capacity to recirculate via HEV. However, recent data in the rat called these results into question. We therefore analyzed the migration properties of murine CD4⁺ T cell subpopulations defined by several markers used to distinguish memory from naive CD4⁺ cells in mice, namely CD45RB, L-selectin and CD44. Our data clearly show that the majority of putative memory cells expressing either low levels of CD45RB, low levels of L-selectin or high levels of CD44 display a strongly reduced capacity for direct entry into lymphoid tissues, including the spleen, from the blood stream. The accumulation in peripheral lymph nodes is further reduced by treatment with anti-L-selectin antibody, which blocks their entry via HEV. This indicates that memory CD4⁺ T cells are not excluded from crossing lymph node HEV, and that the numbers of cells entering the node via this route exceed the numbers entering via the afferent lymph, at least in the absence of local inflammation. Concomitantly, a strongly enhanced localization of cells of the memory phenotype is observed in lung and liver as compared with naive cells. Trafficking to specific sites such as skin or gut mucosa is not a prominent feature of the total population of memory cells. The trafficking to lung and liver and an increased ability to bind to dendritic cells, demonstrable in in vitro adhesion assays, suggest a more sessile phenotype of most memory cells. With respect to these properties, memory cells have a surprizing similarity to fully activated lymphocytes.     

Cell Adhesion Molecule and Lymphocyte Activation Marker Expression during Experimental Vaginal Candidiasis

Cell-mediated immunity by Th1-type CD4(+) T cells is the predominant host defense mechanism against mucosal candidiasis. However, studies using an estrogen-dependent murine model of vaginal candidiasis have demonstrated little to no change in resident vaginal T cells during infection and no systemic T-cell infiltration despite the presence of Candida-specific systemic Th1-type responses in infected mice. The present study was designed to further investigate these observations by characterizing T-cell activation and cell adhesion molecule expression during primary and secondary C. albicans vaginal infections. While flow cytometry analysis of activation markers showed some evidence for activation of CD3(+) draining lymph node and/or vaginal lymphocytes during both primary and secondary vaginal Candida infection, CD3(+) cells expressing the homing receptors and integrins alpha(4)beta(7), alpha(M290)beta(7), and alpha(4)beta(1) in draining lymph nodes of mice with primary and secondary infections were reduced compared to results for uninfected mice. At the local level, few vaginal lymphocytes expressed integrins, with only minor changes observed during both primary and secondary infections. On the other hand, immunohistochemical analysis of vaginal cell adhesion molecule expression showed increases in mucosal addressin cell adhesion molecule 1 and vascular cell adhesion molecule 1 expression during both primary and secondary infections. Altogether, these data suggest that although the vaginal tissue is permissive to cellular infiltration during a vaginal Candida infection, the reduced numbers of systemic cells expressing the reciprocal cellular adhesion molecules may preempt cellular infiltration, thereby limiting Candida-specific T-cell responses against infection.     

In vitro exposure to highly cytopathic HIV-1 X4 strains increases expression of mucosa-associated integrins on CD4(+) T cells

To determine whether infection with HIV-1 strains of different tropisms would influence expression of the mucosa-associated integrins alpha 4 beta 7 and alpha E beta 7 or the lymph node homing receptor L-selectin on peripheral T lymphocytes, cells were infected with the CXCR4-tropic (X4)/syncytium-inducing (SI) HIV-1(IIIB) strain or with X4/SI or CCR5-tropic (R5)/non-SI (NSI) primary human isolates. Flow cytometric analyses of CD4(+) T cells from cultures infected with HIV-1(IIIB) and one X4/SI primary HIV-1 isolate revealed a significant increase in surface expression of alpha 4 beta 7 and alpha E beta 7 12 days after infection. L-selectin expression was not significantly affected on CD4(+) T cells. However, infection with another X4/SI and two R5/NSI primary HIV-1 isolates did not significantly alter homing receptor expression on CD4(+) T cells. Since a higher degree of CD4 cytopathicity occurred in those cultures having increased integrin expression, these data suggest that significantly altered mucosal homing receptor expression on CD4(+) T cells may result as a "bystander" effect after infection with some cytopathic isolates of HIV-1.     

Lymphocyte trafficking: CD4 T cells with a 'memory' phenotype (CD45RC-) freely cross lymph node high endothelial venules in vivo.

Antigen encounter not only induces a change in surface expression of CD45RC isoforms in the rat from a high (CD45RC+) to a low molecular weight molecule (CD45RC-), but also stimulates changes in expression of adhesion molecules that regulate CD4 T-cell migration. T cells with an activated or 'memory' phenotype (CD45RC-) are thought to enter lymph nodes almost exclusively via afferent lymphatics whereas T cells in a resting state (CD45RC+) migrate across high endothelial venules (HEV). The present study monitored the rapid recirculation from blood to lymph of allotype-marked CD45RC T-cell subsets. Surprisingly, we found that CD45RC- CD4 T cells entered the thoracic duct slightly faster and reached peak numbers 3 hr earlier (18 hr) than did the CD45RC+ subset. To determine whether the entrance of CD45RC+ and RC- subsets was restricted to HEV and afferent lymphatics, respectively, recirculation of CD4 T cells was monitored in mesenteric lymphadenectomized (MLNx) rats (on healing the intestinal afferent lymphatics are joined directly to the thoracic duct), or in recipients that had had the mesenteric lymph node (MLN) acutely (2-3 hr) deafferentized (entry would be restricted to HEV). In these studies CD45RC- CD4 T cells entered the MLN across HEV on an equal basis with T cells expressing a CD45RC+ phenotype. Contrary to currently held dogma the results showed that, in vivo, CD4 T cells with a memory phenotype freely enter lymph nodes (LN) across HEV as well as via afferent lymphatics.     

Trafficking of CD44-deficient murine lymphocytes under normal and inflammatory conditions

CD44 has been implicated in hyaluronan (HA)-dependent primary adhesion between leukocytes and endothelium. We studied the trafficking of lymphocytes of CD44-deficient DBA/1 mice under normal conditions, and during chronic and transient forms of inflammation. Animals homozygous for the CD44 mutation (CD44(-/-)) showed no abnormalities in the composition of the lympho-hemopoietic system, but their leukocytes could not recognize HA as an adhesion ligand. T cells from CD44-deficient mice responded normally to immunization with type II collagen or stimulation with a bacterial superantigen. Lymphocytes harvested from naive CD44(-/-) and wild-type (WT) animals showed similar trafficking properties when injected into naive recipients. However, cells from WT and CD44-deficient mice with collagen-induced arthritis showed distinct migration kinetics upon transfer to arthritic recipients. While lymphocytes from CD44(-/-) mice preferentially homed to lymph nodes, their entry into the inflamed synovial joints was delayed as compared with WT cells. Similar differences were observed in the migration kinetics of CD44-deficient and CD44-competent (CD44(+/+)) lymphocytes in bacterial superantigen-induced peritonitis. These results suggest that CD44 plays opposite roles in the regulation of leukocyte traffic to inflammatory sites versus the lymph nodes. CD44-deficient lymphocytes from animals with chronic arthritis, but not from those with transient peritonitis, expressed markedly reduced levels of the lymph node homing receptor, L-selectin. Extreme down-modulation of L-selectin from CD44(-/-) cells in arthritic condition might be a counter-regulatory response, which, by extending lymphocyte transit time in the circulation at the expense of lymph node homing, allows CD44-deficient cells to gain entry to the site of chronic inflammation via secondary adhesion mechanisms.     

Role of L-selectin in the development of autoimmune diabetes in non-obese diabetic mice

Autoimmune diabetes is characterized by an early mononuclear infiltration of pancreatic islets and later selective autoimmune destruction of insulin-producing beta cells. Lymphocyte homing receptors have been considered candidate targets to prevent autoimmune diabetes. L-selectin (CD62L) is an adhesion molecule highly expressed in naive T and B cells. It has been reported that blocking L-selectin in vivo with a specific antibody (Mel-14) partially impairs insulitis and diabetes in autoimmune diabetes-prone non-obese diabetic (NOD) mice. In the present study we aimed to elucidate whether genetic blockade of leukocyte homing into peripheral lymph nodes would prevent the development of diabetes. We backcrossed L-selectin-deficient mice onto the NOD genetic background. Surprisingly NOD/L-selectin-deficient mice exhibited unaltered islet mononuclear infiltration, timing of diabetes onset and cumulative incidence of spontaneous diabetes when compared to L-selectin-sufficient animals. CD4, CD8 T cells and B cells were present in islet infiltrates from 9-week-old L-selectin-sufficient and -deficient littermates. Moreover, total splenocytes from wild-type, heterozygous or NOD/L-selectin-deficient donor mice showed similar capability to adoptively transfer diabetes into NOD/SCID recipients. On the other hand, homing of activated, cloned insulin-specific autoaggressive CD8 T cells (TGNFC8 clone) is not affected in NOD/L-selectin-deficient recipients. We conclude that L-selectin plays a small role in the homing of autoreactive lymphocytes to regional (pancreatic) lymph nodes in NOD mice.     

The human peripheral lymph node vascular addressin. An inducible endothelial antigen involved in lymphocyte homing.

The extravasation of blood-borne lymphocytes into organized lymphoid tissues and sites of chronic inflammation is directed in part by interactions of lymphocyte surface adhesion molecules, known as homing receptors, with tissue-selective endothelial ligands called vascular addressins. In mice and humans, lymphocyte L-selectin and the peripheral lymph node addressin (PNAd) form a homing receptor-endothelial ligand pair involved in lymphocyte traffic to peripheral lymph node (PLN). We have examined the tissue distribution and function of human PNAd, using monoclonal antibody MECA-79 and in vitro assays of L-selectin-dependent lymphocyte binding. We demonstrate that PNAd is expressed by human high endothelial venules (HEV) in lymphoid tissues which support lymphocyte adhesion via a PLN-associated recognition system. MECA-79 inhibits adhesion to these HEV of a cell line that binds predominantly via the PLN-homing receptor, L-selectin, but has no effect on adhesion by a mucosal HEV-binding cell line. Furthermore, MECA-79 blocks binding of human peripheral blood mononuclear cells to both PLN and tonsil HEV, but not significantly to HEV in the appendix. In addition, we demonstrate PNAd induction on venules at chronic inflammatory sites in humans, particularly sites with severe or long-standing chronic inflammatory involvement. These results confirm that PNAd functions as a PLN vascular addressin in humans, and that in addition to directing normal lymphocyte recirculation to lymph nodes and tonsils, this addressin likely participates in lymphocyte recruitment to sites of chronic inflammation.     

Lymphocyte triggering via L-selectin leads to enhanced galectin-3-mediated binding to dendritic cells

For proper immune surveillance, naive lymphocytes are recruited from the blood into secondary lymphoid organs. L-selectin expressed on lymphocytes plays an important role in the initial attachment of these cells to high endothelial venules (HEV) in lymph nodes. Previously, we found that triggering via L-selectin resulted in activation of lymphocytes, followed by an alteration in their adhesion capacity. This suggested that L-selectin triggering might play a role in cell-cell interactions after lymph node entry. Here, we identify a novel adhesion mechanism involving L-selectin-triggered lymphocytes and dendritic cells, and we show that enhanced binding to dendritic cells is mediated by galectin-3 and not by integrins. Furthermore, it was shown that L-selectin-triggered T lymphocytes exhibited enhanced proliferation in an allogeneic mixed lymphocyte reaction. It is concluded that, in addition to a role for L-selectin in tethering and rolling on endothelium, triggering of the molecule on the lymphocyte surface leads to changes that are pertinent for the function of the cell after passing the HEV. We argue that the described adhesion mechanism plays a role in optimizing the initial interaction between dendritic cells and lymphocytes.     

Topographic distribution of homing receptors on B and T cells in human gut-associated lymphoid tissue: relation of L-selectin and integrin alpha 4 beta 7 to naive and memory phenotypes.

In mice, integrin alpha 4 beta 7 is the main receptor used by lymphocytes that home to the Peyer's patches, although L-selectin contributes to the initial interaction with high endothelial venules. Less is known about the expression and function of these adhesion molecules in humans. The distribution of L-selectin and alpha 4 beta 7 on various B- and T-cell subsets was examined in human Peyer's patches (n = 8) and appendix (n = 4), collectively called gut-associated lymphoid tissue. Multicolor immunophenotyping was performed on cryosections, and dispersed cells were examined by flow cytometry. In cryosections, CD45RA+ T cells around and within interfollicular high endothelial venules, as well as surface (s)IgD+ B lymphocytes in the follicle mantles, often expressed abundant L-selectin but only intermediate levels of alpha 4 beta 7. CD45RO+ T cells and sIgD- B cells expressed higher levels of alpha 4 beta 7 and were often located near putative efferent lymphatics; only a small fraction (< 20%) of such memory cells expressed L-selectin. By flow cytometry, considerably more T than B lymphocytes co-expressed L-selectin and alpha 4 beta 7 (40% versus 25% and 67% versus 39%, respectively). In samples with many L-selectin+ cells (> 30%), more of these lymphocytes co-expressed alpha 4 beta 7 than in samples with few L-selectin+ cells. Because L-selectin and alpha 4 beta 7 were co-expressed on lymphocytes located near high endothelial venules, and because such co-expression was relatively common when many L-selectin+ cells were present, both of these molecules might participate in homing to human gut-associated lymphoid tissue. Such homing is probably most pronounced for T lymphocytes that were found to express L-selectin and alpha 4 beta 7 more often than B lymphocytes. The selective and relatively high expression of alpha 4 beta 7 on memory cells located near efferent lymphatics indicated a different migratory capacity; after exit from gut-associated lymphoid tissue, such stimulated cells might home mainly to mucosal effector sites.     

Tissue-specific migration pathways by phenotypically distinct subpopulations of memory T cells.

A proportion of T cells recirculate in a tissue-selective manner. Recent studies which showed that the skin-tropic subset of T cells was of memory/activated type, led us to examine whether the preferential homing of T cells to the gut also involved memory T cells, and if so whether these memory T cells were phenotypically distinct from other memory T cells. Lymphocytes migrating through the gut and the skin of sheep was collected by cannulating the lymphatic ducts draining these tissues. Both naive and memory T cells were found to recirculate through the gut, although only memory T cells migrated through the skin. However, when T cells from the gut were labeled with fluorescein isothiocyanate and assessed for their migration back to the gut, it was the memory population which showed a tropism for the gut. Gut-tropic memory T cells migrated poorly through the skin, indicating that these cells were distinct from skin-tropic memory T cells. This was confirmed by phenotypic analysis. Gut memory T cells expressed very low levels of the alpha 6 and beta 1 integrins, in contrast to skin memory T cells which expressed high levels. There was no evidence for heterogeneity within the naive T cell population, which migrated preferentially to lymph nodes. This migration pattern could be explained in part by the high expression of the L-selectin (lymph node homing receptor, LAM-1) on naive T cells, in contrast to memory T cells from gut or skin which were mostly L-selectin negative. These results in sheep indicate that subsets of alpha/beta memory T cells show tissue-selective migration patterns, which probably develop in a particular environment following encounter with antigen.     

The strict regulation of lymphocyte migration to splenic white pulp does not involve common homing receptors

Although the spleen is the largest secondary lymphoid organ, little is known about the regulation of lymphocyte migration towards its different compartments of red and white pulp, in contrast to the well-studied mechanisms of lymphocyte homing to lymph nodes. Here we show that short-term trypsin treatment of lymphocytes cleaved off molecules involved in entry into lymph nodes, while homing to the splenic white pulp was unaltered. Prolonged trypsin treatment also abolished the ability of lymphocytes to enter the white pulp. Analysis of affected cell surface molecules and adoptive transfer studies in combination with blocking antibodies revealed that l-selectin, CD44, PSGL-1 and the alpha4 integrins are not required for migration to the white pulp. Although lymphocyte function-associated antigen-1 (LFA-1) is critical for entry into lymph nodes, we show here that in the absence of functional LFA-1 molecules, lymphocytes can still enter the white pulp, in spite of the high expression of intercellular adhesion molecule-1 on sinus lining cells in the marginal zone. The data indicate that adhesion molecules involved in lymphocyte homing to lymph nodes are not essential for migration towards the splenic white pulp, but that additional, trypsin-sensitive, and so far unidentified, molecules are required.     

T lymphocyte rolling and recruitment into peripheral lymph nodes is regulated by a saturable density of L-selectin (CD62L)

L-selectin mediates tethering and rolling of lymphocytes in high endothelial venules (HEV) of lymph nodes (LN) and of leukocytes at inflammatory sites. We used transgenic mice expressing varying levels of wild-type or a non-cleavable mutant form of L-selectin on T cells to determine the relationship between L-selectin density, tethering and rolling, and migration into LN. T cells expressing supraphysiological levels of either wild-type or non-cleavable L-selectin showed rolling parameters similar to C57BL/6 T cells in hydrodynamic flow assays and during rolling in Peyer's patch HEV. In contrast, PMA- or antigen-activated T cells and L-selectin(+/-) T cells expressing subphysiological levels of L-selectin showed reduced numbers of rolling cells with increased rolling velocity. Short-term homing studies showed that elevated expression of L-selectin above physiological levels had no effect on T cell migration to LN; however, low L-selectin expression resulted in reduced T cell homing to LN. Thus, T lymphocyte migration into LN is regulated by the density of cell surface L-selectin. In addition, there is a saturable density of L-selectin required for optimal homing to PLN in C57BL/6 mice, the L-selectin level on circulating naive T cells promotes optimal homing, and increased expression above saturating levels promotes no further increase in T cell recruitment.     

Human rotavirus specific T cells: quantification by ELISPOT and expression of homing receptors on CD4+ T cells

Using an intracellular cytokine assay, we recently showed that the frequencies of rotavirus (RV)-specific CD4(+) and CD8(+) T cells secreting INFgamma, circulating in RV infected and healthy adults, are very low compared to the frequencies of circulating cytomegalovirus (CMV) reactive T cells in comparable individuals. In children with acute RV infection, these T cells were barely or not detectable. In the present study, an ELISPOT assay enabled detection of circulating RV-specific INFgamma-secreting cells in children with RV diarrhea but not in children with non-RV diarrhea without evidence of a previous RV infection. Using microbead-enriched CD4(+) and CD8(+) T cell subsets, IFNgamma-secreting RV-specific CD8(+) but not CD4(+) T cells were detected in recently infected children. Using the same approach, both CD4(+) and CD8(+) RV-specific T cells were detected in healthy adults. Furthermore, stimulation of purified subsets of PBMC that express lymphocyte homing receptors demonstrated that RV-specific INFgamma-secreting CD4(+) T cells from adult volunteers preferentially express the intestinal homing receptor alpha4beta7, but not the peripheral lymph node homing receptor L-selectin. In contrast, CMV-specific INFgamma-secreting CD4(+) T cells preferentially express L-selectin but not alpha4beta7. These results suggest that the expression of homing receptors on virus-specific T cells depends on the organ where these cells were originally stimulated and that their capacity to secrete INFgamma is independent of the expression of these homing receptors.     

Blood Leucocyte Subsets of the Rat: Expression of Adhesion Molecules and Localization Within High Endothelial Venules

Although several distinct adhesion pathways are now well characterized, it is not clear whether analysis of adhesion molecule expression on leucocytes is sufficient to predict their interaction with endothelium in vivo. Therefore, in the present study this question was addressed by investigating the interaction between blood leucocyte subsets and high endothelial venules (HEV). The expression of different types of adhesion molecule (CD44, α4-integrins, LFA-1, ICAM-1, CD2 and L-selectin) on lymphocytes, NK cells, monocytes and granulocytes of rat blood was determined by flow cytometry. In the same animals the numbers of blood leucocyte subsets present in the HEV of axillary lymph nodes and Peyer's patches were analysed using immunohistology. In the HEV of both axillary lymph nodes and of Peyer's patches lymphocytes (> 10.000 per mm²), as well as small numbers of NK cells and monocytes (< 500 per mm²), were found. In contrast, granulocytes were not detected here. Lymphocytes, NK cells, monocytes and granulocytes each expressed CD44, α4-integrins, LFA-1, ICAM-1, CD2 and L-selectin in a pattern characteristic to cell type, but this did not correlate with the different ability of the leucocyte subsets to interact with the two types of HEV. In conclusion, determining the expression of CD44, α4-integrins, LFA-1, ICAM-1, CD2 and L-selectin on blood leucocytes alone is not sufficient to predict leucocyte/endothelium interaction in vivo     

Expression of mucosal homing receptor alpha4beta7 is associated with enhanced migration to the Chlamydia-infected murine genital mucosa in vivo

The CD4 T helper cell type 1 (Th1) response is essential for the resolution of chlamydial genital infection in mice. However, not all Th1 clones are equally protective in eradicating the infection. Since oral immunization regimens produce protective immunity, we evaluated the role of the mucosa-associated homing receptor, alpha4beta7, in trafficking to the genital mucosa. Using a panel of CD4, Th1 cell lines and clones, we compared the lymphocyte homing patterns of a Chlamydia-specific, protective clone (P-MoPn), a nonprotective clone (N-MoPn), and a keyhole limpet hemocyanin (KLH)-specific cell line (KLH-1). T cells were labeled with the fluorescent dye PKH-26, adoptively transferred into Chlamydia-infected mice, and monitored at different time points throughout the course of a genital infection. We found that clones P-MoPn and N-MoPn migrated to similar extents to the genital tract and in significantly greater numbers than the KLH-specific T-cell line. Both clones and the KLH-1 line expressed similar levels of the adhesion molecules alpha4, beta1, CD44, and CD11a. However, clones P-MoPn and N-MoPn expressed higher levels of the mucosal homing receptor, alpha4beta7. Also, clones P-MoPn and N-MoPn but not the KLH-1 line migrated to the mesenteric lymph node, suggesting a mucosal recirculation pattern. Moreover, blocking alpha4beta7 adhesion interaction in vivo significantly reduced the recruitment of P-MoPn but not KLH-1 to the genital tract. These findings show that the mucosal homing receptor alpha4beta7 is utilized by a subset of CD4 cells during migration to the Chlamydia-infected genital tract.     

Alpha4beta1 and alpha4beta7 CD4 T cell numbers increase and CLA CD4 T cell numbers decrease in systemic sclerosis

We studied the expression of adhesion molecules affecting recirculation and homing on peripheral blood CD4(+) T cells of patients with systemic sclerosis (SSc), in order to evaluate whether the distribution of tissue targeted subsets could reflect the participation of internal organs or the extent of cutaneous involvement [i.e. limited cutaneous (lc) and diffuse cutaneous (dc)]. Peripheral blood mononuclear cells (PBMC) from 51 patients with SSc and 19 sex- and age-matched controls were investigated by cytofluorimetric analysis for lymphocyte subpopulations carrying the following surface molecules: CD3, CD4, CLA, alpha4beta7 and alpha4beta1. Standard routine biochemistry and clinical examinations were also performed in all patients. We found that both alpha4beta1(+) and alpha4beta7(+) cells within the CD4(+) T cell population were significantly increased, while CLA(+) CD4(+) T cells were significantly reduced in SSc, compared to healthy donors. Significantly lower absolute numbers of alpha4beta7(+) cells were found in lc- compared to dc-SSc. Patients with oesophageal involvement had high numbers of alpha4beta7(+) cells, while those with nephritis also showed low levels of CLA(+) cells. Lung involvement was related directly to alpha4beta1(+) cell numbers and inversely to alpha4beta7(+) CD4 cell numbers. Taken together, our findings demonstrate that distinct CD4(+) T cell populations with selective homing properties show changes from normal distribution in SSc, and such changes are related to clinical expression and organ involvement in the course of the disease.     

小鼠新型黏附分子nepmucin的研究进展

小鼠nepmucin是一种新型黏附分子，胞外区含有一个典型的粘蛋白样结构域和一个V型免疫球蛋白（Ig）结构域，广泛表达于除派氏结（PPs）外的外周淋巴组织和实质性器官，优先表达于各种组织的小血管内皮细胞。该分子可与淋巴细胞归巢的重要分子L-选择素（L—selectin）结合，分别通过粘蛋白样结构域和Ig结构域介导L—selectin依赖的淋巴细胞在血管内皮上的滚动、附着，促进淋巴细胞穿越（TEM）高内皮微静脉（HEV）内皮细胞。小鼠nepmucin与CD31分子在淋巴结HEY内皮细胞的分布相似，且同样发生循环，但其循环机制以及分子循环所发挥的生物学作用尚不清楚。     

Intestinal dendritic cells increase T cell expression of alpha4beta7 integrin

The integrin alpha4beta7 binds to MAdCAM-1 and contributes to homing of lymphocytes to gut and other mucosal tissues. In humans, the alpha4beta7(hi) subset of circulating memory cells appears to have been primed in mucosal tissues. The factors that determine whether alpha4beta7(lo) naive cells become alpha4beta(hi) or alpha4beta7(-) cells upon differentiation are poorly understood but could include an influence of the activating antigen-presenting cell. To address this point, the induction of alpha4beta7 following activation of mouse cells with the APC-dependent stimulus soluble anti-CD3 has been examined. Almost all mouse T cells freshly isolated from mesenteric lymph nodes (MLN) and peripheral (PLN; axillary, brachial and inguinal) lymph nodes stained only weakly for alpha4beta7 but a subpopulation became alpha4beta7(hi) upon activation with anti-CD3 in a cell cycle- and accessory cell-dependent manner. A small proportion (approximately 1.5 %) of the starting cells gave rise to alpha4beta7(hi) cells after culture. A higher proportion of alpha4beta7(hi) cells were generated in MLN than PLN cultures. Peyer's patch cultures gave intermediate values. In crossover experiments, MLN dendritic cells (DC) induced higher proportions and numbers of alpha4beta7(hi) cells than PLN DC irrespective of the source of T cells. Therefore, in addition to their other immunoregulatory roles, DC have the potential to shape immune responses by influencing the homing of the lymphocytes they activate.     

Plasmacytoid dendritic cells employ multiple cell adhesion molecules sequentially to interact with high endothelial venule cells--molecular basis of their trafficking to lymph nodes

Plasmacytoid dendritic cells (pDCs) are natural type I IFN-producing cells found in lymphoid tissues, where they support both innate and adaptive immune responses. They emigrate from the blood to lymph nodes, apparently through high endothelial venules (HEVs), but little is known about the mechanism. We have investigated the molecular mechanisms of pDC migration using freshly isolated DCs and HEV cells. We found that pDCs bound avidly to HEV cells and then transmigrated underneath them. Two observations suggested that these binding and migration steps are differentially regulated. First, treatment of pDCs with pertussis toxin blocked transmigration but not binding. Second, pDCs were able to bind but not to transmigrate under non-HEV endothelial cells, although the binding was observed to both HEV and non-HEV endothelial cells. Antibody inhibition studies indicated that the binding process was mediated by alphaL and alpha4 integrins on pDCs and by intercellular adhesion molecule (ICAM)-1, ICAM-2 and vascular cell adhesion molecule-1 on HEVs. The transmigration process was also mediated by alphaL and alpha4 integrins on pDCs, with junctional adhesion molecule-A on HEV cells apparently serving as an additional ligand for alphaL integrin. These data show for the first time that pDCs employ multiple adhesion molecules sequentially in the processes of adhesion to and transmigration through HEVs.