CD40 LIGAND ACTS AS A COSTIMULATORY SIGNAL FOR NEONATAL THYMIC GAMMA-DELTA T-CELLS

The stimulatory requirements for T cells bearing gamma delta T cell re ceptors are distinct from those of alpha beta T cells. We have analyze d the ability of the CD40 ligand (CD40L) to activate neonatal thymic g amma delta T cells. CD40L is expressed on activated T cells and has be en shown to induce B cell proliferation and Ig secretion as well as mo nocyte activation. We now demonstrate that, in the presence of an anti -TCR-gamma delta Ab, CD40L is able to induce the proliferation of neon atal thymic gamma delta cells. The presence of CD40L also leads to enh anced expression of a variety of activation-associated Ag including CD 25, CD69, CD44, and Ly6C. In addition to proliferation, CD40L induces lectin-mediated cytolytic activity in thymic gamma delta T cells as we ll as the production of lFN-gamma and TNF-alpha. We were unable to det ect IL-2 or IL-4 production in response to CD40L, and Ab-blocking stud ies indicate that the mechanism of activation appears to involve IL-1 but is independent of IL-2, IL-4, and IL-7. These results suggest that , in addition to its effects on B cells and monocytes, CD40L can costi mulate the activation of thymic gamma delta T cells.