Cell-mediated and humoral immune responses in mice. IV. Difference of the functional cell population between helper activity and delayed-type hypersensitivity.

Helper activity in the anti-hapten antibody response was studied in mice in reference to the induction of delayed-type hypersensitivity (DTH) to the carrier protein. Mice were immunized either by an i.v. injection of alum-precipitated bovine serum albumin (AP-BSA) plus bacterial endotoxin or by a s.c. injection of BSA in Freund's complete adjuvant, the latter being effective in inducing DTH. The helper activity was estimated by the antibody response to the challenge with dinitrophenylated BSA (DNP-BSA) given at varying intervals after the injection of BSA. The results indicated that the helper activity was independent of DTH to the carrier protein, suggesting that these two activities, are mediated by different populations of functional cells. A low dose of tolerogenic soluble BSA (sBSA) was sufficient to abrogate the helper activity in the response to DNP-BSA. In contrast, DTH to BSA was only partially depressed by the pretreatment with a low dose of sBSA and was completely depressed by a high dose. DTH reactivity in mice pretreated with a low dose of tolerogen and followed by the immunization with BSA in Freund's complete adjuvant was substantiated by the microscopic observation of mononuclear cell infiltration at the site of the test antigen injection. These results suggest that cells involved in the helper function and DTH may be derived from different precursors.