Ox40-ligand has a critical costimulatory role in dendritic cell: T cell interactions

The tumor necrosis factor family molecule Ox40-ligand (Ox40L) has been iden tified as a potential costimulatory molecule and also has been implicated i n T cell homing and B cell activation. To ascertain the essential functions of Ox40L, we generated and characterized Ox40L-deficient mice. Mice lackin g Ox40L exhibit an impaired contact hypersensitivity response, a dendritic cell-dependent T cell-mediated response, due to defects in T cell priming a nd cytokine production. In contrast, Ox40L-deficient mice do not have defec ts in T cell homing or humoral immune responses. In vitro, Ox40L-deficient dendritic cells are defective in costimulating T cell cytokine production. Thus, Ox40L has a critical costimulatory function in vitro and in vivo for dendritic cell:T cell interactions.