Regulation of in vitro and in vivo T cell activation by CD43

Accessory molecule interactions can be critical in determining the outcomeof a T cell's encounter with antigen. Cell adhesion proteins may augment Tcell responses by facilitating TCR engagement of the antigen-MHC complex,while co-stimulatory molecules may deliver distinct signals that modulate Tcell responsiveness. CD43 (leukosialin, sialophorin) has been suggested toinfluence cell activation by steric hindrance based upon the large size andglycosylation of the protein, as well as the relative abundance of theprotein on the cell surface. In this paper we examine both in vitro and invivo T cell-dependent responses in CD43-deficient mice. We demonstrate thatT cells from CD43-deficient mice are hyper-responsive following both invivo and in vitro activation, and that this is observed in response to notonly TCR-CD3-mediated stimulation, but also following receptor-independentactivation. This data suggests that mechanisms other than non-specificsteric hindrance are important in the regulation of T cell activation byCD43.