The genetic restrictions of the activation of third-order suppressor cells (Ts3) were studied in mice, using two different types of anti-azobenzenearsonate (ABA)-immune responses, namely delayed-type hypersensitivity (DTH) and cytotoxic T lymphocyte (CTL) generation. Ts2 cells were induced in several different strains of mice by injecting monoclonal T hybridoma molecules or first-order suppressor factors (TsF1) originating in A/J (H-2a, Igh-1e) mice and then testing the TsF2 molecules derived from these Ts2 in A/J and A.By (H-2b, Igh-1e) or (A/J X A.By)F1 (H-2a/b, Igh-1e) and (C57Bl/6 X A/J)F1 (H-2b/a, Igh-1e) mice. It was shown that the activity of TsF2 was restricted to the I-J of the strain in which Ts2 was induced. By genetic analysis, restriction was shown to be due to the requirement of H-2 identity between ABA-coupled cells used for Ts3 activation and the strain of the TsF2 origin. Moreover, by using H-2-congenic ABA-coupled cells, we were also able to precisely map and demonstrate that ABA-coupled cells I-J identical to TsF2 induced in various strains were necessary for effective suppression to occur. This selective activation of Ts3 suggested the existence of I-J-related antigen presentation for suppression as the counterpart of I-A or I-A-I-E-restricted antigen presentation for positive immune responses.

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