Different Effects of the Capsular Polysaccharide of Klebsiella pneumoniae on the Functions of Various Subpopulations of B Cells in the Immune Response of Mice to T‐Dependent Antigen

Abstract

AbstractUsing the capsular polysaccharide of Klebsiella pneumoniae (CPS‐K) as a polyclonal B‐cell activator (PBA) and sheep red blood cells (SRBC) as a T‐dependent antigen, we studied the effects of PBA on the functions of various subpopulations of B cells in the immune response of mice to T‐dependent antigen. Antibody‐forming cells (AFC) of IgM and IgG types were estimated as anti‐SRBC direct and indirect plaque‐forming cells (PFC), and the B cells with precursor activities involving generation of AFC and supplementing new B cells as rosette‐forming cells (RFC) of the B‐cell type. Stimulation of normal mice by CPS‐K caused a definite increase in the number of direct PFC but not in that of indirect PFC and RFC in the spleens. The responsiveness of spleen cells of CPS‐K‐treated mice to generate PFC and RFC responses to a subsequent injection of SRBC was lower than that of CPS‐K‐untreated normal mice. In this case, the responsiveness to generate RFC and indirect PFC was inhibited more strongly by CPS‐K than that to generate direct PFC. When CPS‐K was injected into normal mice simultaneously with SRBC, CPS‐K never decreased but increased the levels of PFC and RFC responses to SRBC. In the spleens of SRBC‐primed mice, the number of RFC was markedly decreased following injection of CPS‐K, the number of direct PFC was increased only slightly and the number of indirect PFC was increased very slightly. The responsiveness of spleen cells of these CPS‐K‐treated SRBC‐primed mice to generate secondary PFC and RFC responses to a subsequent injection of SRBC was much lower than that of CPS‐K‐untreated SRBC‐primed mice. In this case, the responsiveness to generate the secondary RFC and indirect PFC responses was more strongly inhibited by CPS‐K than that to generate the secondary direct PFC response. When CPS‐K was injected into SRBC‐primed mice simultaneously with the secondary injection of SRBC, there were marked decreases in the level of the secondary RFC response and slight decreases in that of the secondary indirect PFC response, but little change in that of the secondary direct PFC response. From these results it has been concluded that CPS‐K provides the positive signal (the minor action) and the negative signal (the major action) to various subpopulations of B cells functioning at various stages of the immune response to T‐dependent antigen in different ways, and acts to regulate the levels of B‐cell responses to the antigen‐mediated positive signal.