Junctional adhesion molecule-C regulates the early influx of leukocytes into tissues during inflammation.

Leukocyte recruitment from blood to inflammatory sites occurs in a multistep process that involves discrete molecular interactions between circulating and endothelial cells. Junctional adhesion molecule (JAM)-C is expressed at different levels on endothelial cells of lymphoid organs and peripheral tissues and has been proposed to regulate neutrophil migration by its interaction with the leukocyte integrin Mac-1. In the present study, we show that the accumulation of leukocytes in alveoli during acute pulmonary inflammation in mice is partially blocked using neutralizing Abs against JAM-C. To confirm the function of JAM-C in regulating leukocyte migration in vivo, we then generated a strain of transgenic mice overexpressing JAM-C under the control of the endothelial specific promotor Tie2. The transgenic animals accumulate more leukocytes to inflammatory sites compared with littermate control mice. Intravital microscopy shows that this is the result of increased leukocyte adhesion and transmigration, whereas rolling of leukocytes is not significantly affected in transgenic mice compared with littermates. Thus, JAM-C participates in the later steps of the leukoendothelial adhesion cascade.

PECAM-1, alpha6 integrins and neutrophil elastase cooperate in mediating neutrophil transmigration.

The heterogeneous nature of the perivascular basement membrane (composed primarily of laminin and collagen type IV) suggests the existence of an elaborate array of adhesive interactions and possibly proteolytic events in leukocyte migration through this barrier. In this context, blockade of alpha6 integrins (laminin receptors), neutrophil elastase (NE) or both inhibited neutrophil migration through interleukin-1beta (IL-1beta)-stimulated mouse cremasteric venules, as observed by intravital microscopy. Furthermore, analysis of tissues by confocal microscopy indicated a synergistic role for alpha6 integrins and NE in mediating neutrophil migration through the perivascular basement membrane. Using a combined in vitro and in vivo experimental approach, the findings of this study also suggest that alpha6 integrins and NE are mobilized from intracellular stores to the cell surface of transmigrating mouse neutrophils, although these events occur via mechanisms dependent on and independent of platelet/endothelial-cell adhesion molecule 1 (PECAM-1, CD31), respectively. Despite different regulatory mechanisms, blockade of alpha6 integrins or NE inhibited migration of murine neutrophils through laminin-coated filters in vitro. Collectively, the findings suggest that, whereas regulation of the expression of alpha6 integrins and NE occur via different adhesive mechanisms, these molecules might act in a cooperative manner in mediating neutrophil migration through venular walls, in particular the perivascular basement membrane.

Blockade of alpha6 integrin inhibits IL-1beta- but not TNF-alpha-induced neutrophil transmigration in vivo.

In vitro and in vivo evidence supports a functional role for the integrin alpha6beta1 in neutrophil migration through the perivascular basement membrane, a response that in vivo appears to be associated with platelet/endothelial cell adhesion molecule-1 (PECAM-1)-mediated up-regulation of alpha6beta1 on the cell surface of transmigrating leukocytes. As the involvement of PECAM-1 in leukocyte migration is cytokine-specific, the aim of the present study was to investigate whether alpha6beta1 exhibited a similar profile of stimulus specificity in this context. The cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha) were used to elicit neutrophil migration in two murine models of inflammation, migration through cremasteric venules, as observed by intravital microscopy, and migration into the peritoneal cavity. The role of alpha6beta1 was investigated using an alpha6 integrin-blocking monoclonal antibody GoH3. In both models, GoH3 significantly inhibited neutrophil transmigration induced by IL-1beta but not TNF-alpha. This cytokine-specific role of alpha6 integrin was associated with enhanced cell-surface expression of alpha6beta1 on transmigrated neutrophils (as compared with blood cells) in response to IL-1beta but not TNF-alpha. Using lipopolysaccharide as an inflammatory stimulus in the cremaster muscle model, the study also provides evidence for the involvement of alpha6 integrin in leukocyte transmigration as mediated by endogenously generated IL-1beta. Collectively, the findings demonstrate that alpha6beta1 blockade inhibits neutrophil migration induced by exogenous and endogenous IL-1beta but not TNF-alpha, observations that are associated with increased expression of the integrin on transmigrated leukocytes.

P-selectin mediates IL-13-induced eosinophil transmigration but not eotaxin generation in vivo: a comparative study with IL-4-elicited responses.

The study investigated the role of P-selectin in the responses of eosinophil transmigration and eotaxin generation in vivo elicited by interleukin (IL)-13, as compared with IL-4. Two murine models of leukocyte transmigration were used, migration into cytokine-stimulated peritoneal cavities and through stimulated cremasteric venules, as observed by intravital microscopy. In mice lacking P-selectin, eosinophil infiltration elicited by the cytokines in the peritonitis model was totally inhibited. In the cremaster muscle, however, although spontaneous leukocyte-rolling flux and stimulated leukocyte firm adhesion were inhibited by approximately 97% and approximately 48%, respectively, stimulated transmigration was unaffected. However, IL-13-induced leukocyte transmigration was totally blocked in P-selectin-deficient mice treated with an anti-alpha(4) integrin monoclonal antibody (mAb; PS/2). In comparison, treatment of wild-type mice with the anti-alpha(4) integrin mAb resulted in only partial suppression of IL-13-induced leukocyte transmigration. Significant levels of eotaxin were detected in response to IL-13/IL-4 in both tissues in P-selectin-deficient animals. In conclusion, the regulatory role of P-selectin in leukocyte transmigration elicited by IL-13 appears to be tissue-specific, a phenomenon that is independent of the ability of the cytokine to stimulate eotaxin generation.