Impairment of T cell interactions with antigen‐presenting cells by immunosuppressive drugs reveals involvement of calcineurin and NF‐κB in immunological synapse formation

A stable supramolecular cluster in T cells at the contact site of APCs, the immunological synapse (IS), is essential for full T cell activation. Failure of IS maturation, as determined by defective relocalization of the TCR/CD3 complex at the T cell/APC contact site, is linked with T cell hyporesponsiveness. The effects of clinically used immunosuppressants on these critical events, however, are undefined. Here, we show that treatment of T cells with cyclosporin A, FK506, and dexamethasone, which are known to inhibit calcineurin and NF‐κB, respectively, but not rapamycin, the inhibitor of mammalian target of rapamycin, selectively prevented TCR/CD3 relocalization into the IS, while relocalization of adhesion and cytoskeletal proteins as well as T cell/APC conjugate formation remained unaltered. The involvement of calcineurin and NF‐κB in IS maturation was confirmed by using specific inhibitors of these molecules (FR901725, gossypol, SN50). FK778, as an inhibitor of DNA replication and also TCR/CD3‐activated tyrosine kinases, globally abrogated cytoskeletal, adhesion, and signaling molecule relocalization, thereby preventing formation of an IS at an earlier, immature stage along with impaired, antigen‐specific T cell/APC conjugate formation. Collectively, blocking IS formation at distinct stages may mediate effects on T cell activation of currently used immunosuppressants, apart from their capacity to block gene transcription, cytokine signaling, and DNA replication. Furthermore, these data imply novel functions of calcineurin and NF‐κB for successful IS maturation.