Costimulatory molecules in T cell activation

It is now well established that activation and differentiation of T cells p lay a critical role in the pathogenesis of allergic airway disease. Upon en counter with the specific antigen, naive T helper precursor cells become ac tivated, an event that is regulated not only by engagement of the TCR with the peptide presented in the context of MHC class II molecules but by a num ber of costimulatory signals. The most important costimulatory signal deliv ered to resting T cells occurs upon CD28 engagement by B7 molecules. Howeve r, largely as a consequence of the unraveling of the human genome, it is no w becoming clear that other related members not only of the CD28/B7 family, but also the IL-1 and TNF receptor family also play important roles in pro viding both unique and complementary signals required for optimal T cell ac tivation.