Junctional adhesion molecule (JAM)-B supports lymphocyte rolling and adhesion through interaction with α4β1 integrin

P>Junctional adhesion molecule-A (JAM-A), JAM-B and JAM-C have been implicated in leucocyte transmigration. As JAM-B binds to very late activation antigen (VLA)-4, a leucocyte integrin that contributes to rolling and firm adhesion of lymphocytes to endothelial cells through binding to vascular cell adhesion molecule (VCAM)-1, we hypothesized that JAM-B is also involved in leucocyte rolling and firm adhesion. To test this hypothesis, intravital microscopy of murine skin microvasculature was performed. Rolling interactions of murine leucocytes were significantly affected by blockade of JAM-B [which reduced rolling interactions from 9 center dot 1 +/- 2 center dot 6% to 3 center dot 2 +/- 1 center dot 2% (mean +/- standard deviation)]. To identify putative ligands, T lymphocytes were perfused over JAM-B-coated slides in a dynamic flow chamber system. JAM-B-dependent rolling and sticking interactions were observed at low shear stress [0 center dot 3 dyn/cm(2): 220 +/- 71 (mean +/- standard deviation) versus 165 +/- 88 rolling (P < 0 center dot 001; Mann-Whitney rank sum test) and 2 center dot 6 +/- 1 center dot 3 versus 1 center dot 0 +/- 0 center dot 7 sticking cells/mm(2)/min (P = 0 center dot 026; Mann-Whitney rank sum test) on JAM-B- compared with baseline], but not at higher shear forces (1 center dot 0 dyn/cm(2)). As demonstrated by antibody blocking experiments, JAM-B-mediated rolling and sticking of T lymphocytes was dependent on alpha 4 and beta 1 integrin, but not JAM-C expression. To investigate whether JAM-B-mediated leucocyte-endothelium interactions are involved in a disease-relevant in vivo model, adoptive transfer experiments in 2,4,-dinitrofluorobenzene (DNFB)-induced contact hypersensitivity reactions were performed in mice in the absence or in the presence of a function-blocking JAM-B antibody. In this model, JAM-B blockade during the sensitization phase impaired the generation of the immune response to DNFB, which was assessed as the increase in ear swelling in untreated, DNFB-challenged mice, by close to 40% [P = 0 center dot 037; analysis of variance (anova)]. Overall, JAM-B appears to contribute to leucocyte extravasation by facilitating not only transmigration but also rolling and adhesion.