MURINE T-HELPER CELL-2 LYMPHOCYTES EXPRESS TYPE-I AND TYPE-II IL-1 RECEPTORS, BUT ONLY THE TYPE-I RECEPTOR MEDIATES COSTIMULATORY ACTIVITY

The role of IL-1 in augmenting the Ag receptor-initiate activation pro gram was evaluated in IL-4-producing (Th2) CD4+ murine T lymphocytes. Northern blot and I-125-labeled IL-1alpha cross-linking analyses demon strated that Th2 lymphocytes express both type I and type II IL-1R. Th e expression of both IL-1R isoforms on the surface of the Th2 cells is coordinately up-regulated in response to anti-CD3 cross-linking in th e absence of detectable accessory cells. Analyses of the kinetics of I L-1R acquisition demonstrated that the peak level of type I and type I I IL-1R mRNA expression occurs after the peak expression of mRNA encod ing IL-2Ralpha and IL-4, which are two IL-1-responsive events in the T h2 activation program. Type I IL-1 R ligand-binding antagonists, IL-1R antagonist and anti-type I mAb, were used to evaluate the functional significance of Th2 cell expression of two IL-1R isoforms. The additio n of either IL-1R antagonist or anti-type I mAb completely inhibited t he IL-1alpha-augmented component of the proliferative response stimula ted by anti-CD3 plus exogenous IL-1alpha. Together, these studies indi cate that, although Th2 clones express inducible levels of both type I and type II IL-1R isoforms, the IL-1-induced intracellular signals in volved in augmenting an anti-CD3-stimulated proliferative response are mediated solely through the type I IL-1R.