EphA and ephrin-A proteins regulate integrin-mediated T lymphocyte interactions.

Progressive interaction with other cells is critical to all aspects of T-cell biology - from migration through tissues, to recognition of antigen-presenting cells. We demonstrate a novel mechanism for regulating T lymphocyte adhesion and thus cell-cell interactions, showing that T-cell-expressed EphA and ephrin-A proteins not only regulate adhesive properties, but do so in a diametrically opposing fashion. Integrin-mediated adhesion is stimulated by ephrin-A activation, while EphA signalling is inhibitory. Increasing ephrin-A expression enhances T-cell interactions not only with purified integrin ligands but also endothelial cells, while EphA activation down-regulates these interactions. In accordance with an in vivo role for these proteins in regulating cell-cell interactions, activation of ephrin-A signalling was found to alter the trafficking of injected T lymphocytes to peripheral lymph nodes in vivo. Given the ubiquitous nature of EphA/ephrin-A expression in tissues, these proteins likely play a significant role in regulating T-cell interactions.