Induction and persistence of suppression of contact hypersensitivity against bystander haptens and alloantigens in rats.

The shift of suppression from a tolerizing hapten to a so-called bystander antigen was investigated in this study using contact hypersensitivity to trinitrochlorobenzene (TNCB) and dinitrofluorobenzene (DNFB) and delayed type hypersensitivity (DTH) to alloantigens in the rats as experimental models. Primary suppression of contact hypersensitivity was induced by intravenous injection of the water-soluble forms of TNCB and DNFB. A shift of the suppression to the bystander hapten was found if the tolerizing and bystander hapten were mixed and applied to the same area of skin during the sensitization procedure, but not if they were applied to separate areas of skin. With alloantigens, bystander suppression developed only when the sensitizing allogeneic cells were mixed with hapten-modified syngeneic cells. It was not induced by hapten-modified allogeneic cells. Once induced, such bystander suppression of the response to haptens persisted independently of the primarily tolerizing hapten, and it could be adoptively transferred with spleen cells. These results favour the concept that the bystander suppression is mediated by the non-specific action of suppressor cells generated specifically during the mixed sensitization rather than by an antigen bridge.