REGULATION OF IN-VITRO AND IN-VIVO T-CELL ACTIVATION BY CD43

Accessory molecule interactions can be critical in determining the out come of a T cell's encounter with antigen, Cell adhesion proteins may augment T cell responses by facilitating TCR engagement of the antigen -MHC complex, while co-stimulatory molecules may deliver distinct sign als that modulate T cell responsiveness. CD43 (leukosialin, sialophori n) has been suggested to influence cell activation by steric hindrance based upon the large size and glycosylation of the protein, as well a s the relative abundance of the protein on the cell surface. In this p aper we examine both in vitro and in vivo T cell-dependent responses i n CD43-deficient mice. We demonstrate that T cells from CD43-deficient mice are hyper-responsive following both in vivo and in vitro activat ion, and that this is observed in response to not only TCR-CD3-mediate d stimulation, but also following receptor-independent activation. Thi s data suggests that mechanisms other than non-specific steric hindran ce are important in the regulation of T cell activation by CD43.