CD27/CD70 Interaction Contributes to the Activation and the Function of Human Autoreactive CD27+Regulatory T Cells

CD27, a tumor necrosis factor receptor family member, is a costimulatory molecule for T and B cell activation. We demonstrate here that CD27 signaling is critical for T cell activation in the autologous mixed lymphocyte reaction (aMLR) and for aMLR-induced generation of regulatory T cells that suppress pokeweed mitogen-driven immunoglobulin G synthesis by B cells. Moreover, CD27, expressed on CD45RA+CD4+T cells, is directly involved in the suppressor function of aMLR-activated CD4+T cells, probably by interfering with the interaction between CD70, the CD27 ligand, expressed on CD45RO+CD4+helper T cells, and CD27, expressed on B cells. CD8+T cells, which are required in this system to obtain suppression, on the other hand, do not need CD27 engagement to exert their suppressor function.