Response of rat blood, spleen, and lymph node leucocytes to soluble and insoluble antigen.

Solubilized sheep erythrocyte stroma was found to be antigenic in rats. Spleen and lymph nodes of rats injected with this antigen contained more 7S than 19S plaque-forming cells throughout the primary and secondary responses. When compared to the primary response, secondary immunization with this antigen elicited increased numbers of both 19S and 7S plaque-forming cells. Antibody synthesizing leucocytes in the blood during the primary and secondary responses were predominantly 7S producers during the first few days. Later 19S producers predominated. Intact sheep erythrocytes elicited the same pattern of 19S and 7S antibody-forming cell development in the lymph nodes and blood of intravenously injected rats, but during the early primary response in the spleen there was a predominance of 19S over 7S plaque-forming cells. The 7S cells were in a majority during the entire secondary response of the spleen to intact erythrocytes. The secondary response of spleen and lymph node to intact erythrocytes showed an elevated 7S plaque forming cell response but the number of 19S cells was similar to that detecred after primary immunization. The appearance of haemolytic and haemagglutinating 19S and 7S antibody to sheep erythrocytes or solubilized stroma generally reflected the cellular picture of the spleen. By using an anti-7S globulin it was found that 19S and 7S antibody appeared simultaneously in the serum. After immunization of rats with intact erythrocytes or solubilized stroma the number of lymphoid cells that took up tritiated thymidine was about one hundred-fold greater than the number of antibody-forming cells as determined by localized haemolysis in gel. The number of lymphoid cells positive in an immunocyto-adherence assay was more closely related to the number of cells taking up tritiated thymidine. The passive transfer of spleen cells from rats immunized to sheep erythrocytes showed the number of circulating antibody-forming cells in the normal and irradiated recipients to be related to the concentration of antibody-forming cells localizing in the recipient spleen. The number of antibody-forming cells in the peripheral blood was greater in splenectomized recipients. Irradiation had no effect on the number of antibody-forming leucocytes in the circulation of the splenectomized recipients.