The delayed-type hypersensitivity response to (4-hydroxy-3-nitrophenyl) acetyl- (NP) coupled proteins is carrier-specific: in vivo and in vitro demonstrations.

In vivo and in vitro approaches for measuring DTH to NP and the cross-reactive hapten, NIP, were taken. Mice were immunized subcutaneously with NP-OVA, NP-BGG or NP-CGG in CFA or NP-spleen cells, challenged intradermally with NP or NIP-coupled to a heterologous carrier, and footpad or ear swelling determined 4, 24, and 48 h later. Alternatively, draining LNC were removed and challenged in vitro with either haptenated protein or haptenated, irradiated, syngeneic spleen cells to induce lymphotoxin (LT) production or proliferation. Our results show that although carrier-specific DTH responses are easily elicited both in vivo and in vitro, NP-specific DTH effector cells cannot be evoked by conventional immunization regimens. This failure to induce hapten-specific DTH is not due to suppressor mechanisms. Attempts to induce LT production and T cell proliferation by re-exposure to NP were unsuccessful. Immunization with NP-coupled protein in CFA does elicit an intense Arthus reaction when mice are challenged with the hapten 8 days later. The antibody-mediated nature of this hapten-specific response is indicated by the kinetics of the reaction, which peaks 4 hr after challenge, intensely positive ELISA of circulating anti-NP antibodies, sensitivity to pretreatment with a high dose of cyclophosphamide, and the ability to transfer the reaction to naive recipients with serum. This early response is highly cross-reactive with NIP and is not restricted to mice of the igh-1b allotype.