Cellular aspects of non-specific stimulation of antibody production by capsular polysaccharide of Klebsiella pneumoniae.

Comparative studies were made of the increase in the numbers of plaque-forming cells (PFC), rosette-forming cells (RFC) and haemolytic foci for erythrocyte antigens in the spleens of mice given a non-specific stimulus (the capsular polysaccharide of (CPS-K)) and an antigenic stimulus (sheep red blood cells (SRBC)). The number of direct PFC for SRBC was increased by injection of CPS-K to as high a level as that obtained by injection of SRBC. In contrast, by injection of CPS-K the numbers of indirect PFC, RFC (probably the antibody-forming cell precursors) and haemolytic foci were not increased significantly, whereas all of them were increased markedly by injection of SRBC. The maximal number of PFC in mice injected with CPS-K was approximated to the number of background RFC of the same mice. Injection of CPS-K generated 25–130 times more direct PFC for each of three kinds of erythrocyte antigens, SRBC, rabbit red blood cells and chick red blood cells, than background PFC, whereas the total number of spleen cells was not increased significantly or increased very slightly. Repeated injections of CPS-K were not significantly more effective for increase in the number of direct PFC than a single injection of CPS-K. Injection of CPS-K could generate many direct PFC in mice which had been thymectomized, irradiated and reconstituted with foetal liver cells. In mice injected with CPS-K, increase in (or maintenance of) the numbers of direct PFC and RFC were inhibited by injection of a mitogen inhibitor, vinblastine sulphate, but their sensitivities to the drug were less than those found in mice immunized with SRBC. It has been concluded from these results that in mice injected with CPS-K a large number of antibody-forming cell precursors are differentiated to direct PFC through one division or a few divisions of the individual cells, and that the inability of CPS-K to induce sufficient cell divisions of the individual precursor cells is the cause of the lack of increase in the number of indirect PFC and in immunological memory for secondary PFC responses in mice injected with CPS-K.