Cell surface expression of I-A products is required for contact sensitivity induction by trinitrophenyl-coupled epidermal cells.

Trinitrophenyl (TNP)-couple epidermal cells (EC) injected subcutaneously (s.c.) were more capable of inducing contact sensitivity (CS) to 2, 4, 6-trinitro-1-chlorobenzene (TNCB) than similarly substituted spleen cells (TNP-SC). Furthermore, the intravenous (i.v.) or intraperitoneal (I.P) injection of TNP-EC also induced CS response, whereas the i.v. or i.p. injection of TNP-SC failed to induce them. Treatment of mice with cyclophosphamide (Cy; 50 mg/kg) or anti- I-J serum allowed animals injected with TNP-SC i.v. to develop significant CS responses, suggesting that Cy-sensitive and I-J positive regulatory cells were involved in the induction of unresponsiveness by the I.V. injection of TNP-SC. Mapping studies o the major histocompatibility gene complex (MHC) region demonstrated that identity at the I-A subregion alone between EC donor and recipient mice was sufficient for the induction of CS by TNP-EC given i.v. Blocking experiments using antisera in the absence of complement indicated that I-A subregion-encoded antigens on the surface of TNP-EC apparently are involved in the induction of CS, and are not simply phenotypic markers on the surface of accessory cells.