[Comparative studies on delayed type hypersensitivity of low-molecular compounds and compound-protein conjugates in...

Comparative studies on immunogenicity for compounds (TNBS, CET and 4-AAP) and compound-protein conjugates (TNBS-OA, CET-OA and 4-AAP-OA) were undertaken by the assay systems of humoral reaction (HA) and cellular reaction (DTH) in rabbits. The immunogenicity of TNBS-OA was substantially different from either that of CET-OA or 4-AAP-OA in the assay system of DTH. That is, rabbits immunized with TNBS-OA plus FCA displayed positive DTH reactions to the eliciting antigen (TNBS), while such reactions were never recognized in the rabbits immunized with CET-OA plus FCA or 4-AAP-OA plus FCA to the eliciting antigen of CET or 4-AAP, respectively. The above negative reactions observed in both groups, CET-OA and 4-AAP-OA, can be explained by the ordinary interpretation that the specificity of cellular immunoreaction (DTH) is directed toward the binding part of hapten-protein conjugate. By contrast, TNBS, spread on the skin to evoke DTH, may react with epidermal proteins in vivo to form 2,4,6-trinitrophenyl (TNP)-coupled protein. Consequently, it was suggested that this TNP-coupled protein evoked the positive DTH reaction in the TNBS-OA group.