Role of CD80, CD86, and CTLA4 on mouse $CD4^+ T$ lymphocytes in enhancing cell-cycle progression and survival after activation with PMA and ionomycin

Cell surface interactions between the T cell costimulatory receptors, CD28 and cytotoxic T-lymphocyte antigen-(CTLA4), with their cognate ligands, CD80 and CD86, on antigen-presenting cells play an important role in T cell activation. Although CD80 and CD86 are induced on T cells after activation, not much is known about their role in modulating T cell function. We show that CD80, CD86, and CTLA4 are induced on purified CD4 T cells after in vitro activation with phorbol 12-myristate 13-acetate (PMA) and ionomycin,and they play an essential role for proliferation and survival. Blockade of CTLA4-CD80/CD86 interactions greatly reduces PMA and ionomycin-mediated mouse CD4 T cell activation. The three key features of this inhibition of activation are: First,late events in T cell activation (after 18 h) are affected; second, these cells do not undergo anergy; and third, CD4CD25 regulatory T cells are not responsible. Activation of T cells with PMA and ionomycin together with CTLA4-CD80/CD86 blockade results in decreased induction of CD25 and Bcl-XL, reduced interleukin (IL)-2, and enhanced transforming growth factor- (TGF-) production.Furthermore, extended CTLA4-CD80/CD86 blockade results in decreased cell-cycle progression and enhanced apoptosis in a large proportion of cells. This inhibition of T cell proliferation can be rescued completely with anti-CD28 or IL-2 and partially with TGF- antagonists. This study reveals a functional role for CD80, CD86,and CTLA4 on CD4 T lymphocytes and sheds light on the mechanisms by which these molecules enhance activation and survival with PMA and ionomycin. J. Leukoc. Biol. 72: 921-931; 2002