Residual immunogenicity of irradiated spleen cell suspensions after a single intravenous injection of sheep red blood cells in mice.

Studies were carried out to characterize the residual immunogenicity located in spleen cells of mice after one single intravenous injection of SRBC. An in vivo system was applied for initiation and expression of the immune response consisting of one intraperitoneally injection of spleen cell suspension from SRBC-injected mice in separate groups of recipients in which DTH and secondary humoral response were measured, respectively: six days or four days after the transfer of irradiated spleen cell suspension, the separate groups of recipients being either pretreated with cyclophosphamide (200 mg/kg) or primed with 5 X 10(5) SRBC. The residual immunogenicity was found to be located in a population of radio-resistant (10,000 rads) adherent spleen cells. The same population derived from naive mice injected together with the native antigen did not modify the immune response as compared with those induced by the antigen alone. Furthermore, irradiated spleen cell suspensions from SRBC-injected mice were not able to transfer adoptively DTH sensitivity in naive recipients. Accordingly to the test used to evaluate the residual immunogenicity, it was found that the kinetics of residual immunogenicity able to induce DTH was different from those which stimulate the secondary humoral response. Furthermore, it was found that distinct variations of residual immunogenicity for DTH and antibody formation were induced by varying host manipulations, such as non-specific stimulation of the reticulo-endothelial system, specific activation of T cells involved in DTH or helper function or induction of a state of anergy. It appears, therefore, that the same population of radio-resistant adherent spleen cells are able to induce an immune response and to dispatch information to cells involved in DTH or those involved in antibody synthesis. Moreover, depending upon conditions of immunization, varying subsets of T cells are able to modify the dispatching function of these cells in the processing or presentation of antigen to committed or non-committed lymphocytes.