Oral tolerance to haptens: intestinal epithelial cells from 2,4‐dinitrochlorobenzene‐fed mice inhibit hapten‐specific T cell activation in vitro

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Abstract
The mechanisms underlying the induction of immunological tolerance after feeding soluble exogenous antigens, including proteins and haptens, are still unclear. Using a model of oral tolerance to the contact‐sensitizing hapten 2,4‐dinitrochlorobenzene (DNCB), we have compared the ability of intestinal epithelial cells and of Peyer's patch APC to present DNCB in vitro or ex vivo after oral feeding, to specific peripheral lymph node T cells from DNCB‐sensitized mice. In contrast to Peyer's patch APC, which induce efficient hapten‐specific T cell activation upon exposure to the hapten either in vitro or in vivo, mature MHC class‐II‐positive intestinal epithelial cells were unable to induce T cell activation in either case. Interestingly, enterocytes from DNCB‐fed mice exerted a dramatic inhibitory effect on the proliferative response of hapten‐primed T cells in response to dinitrobenzene sulfonate presented by syngeneic spleen cells. This inhibitory effect, which was also observed with supernatant of intestinal epithelial cells from DNCB‐fed mice, could be reversed by neutralizing anti‐transforming growth factor (TGF)‐β antibodies. In addition, pre‐incubation of hapten‐sensitized T cells with enterocytes from DNCB‐fed mice induced T cell anergy, which could be reversed by exogenous interleukin‐2 or interleukin‐4. These data demonstrate that intestinal epithelial cells activated in vivo by oral administration of DNCB are able to block proliferation of activated T cells through secretion of immunosuppressive cytokines such as TGF‐β. It is proposed that intestinal epithelial cells may play a significant role in oral tolerance by limiting T cell‐mediated hypersensitivity responses.