Further Studies on Generation of Macrophages in In Vitro Cultures of Mouse Spleen Cells and Its Inhibition by the Capsular Polysaccharide of Klebsiella pneumoniae

Abstract

AbstractAlthough the number of macrophages detected in cultures of mouse spleen cells at the start of the culture was very small, it markedly increased during further incubation. Macrophages were generated not only from the glass‐adherent cell fraction of spleen cells, but also from the nonadherent cell fraction obtained after removal of adherent cells either by incubating in glass petri dishes or by passing through a glass bead column. The generation of macrophages from the nonadherent cell fraction occurred even when it was separated as late as 48 hr after the start of the culture. The phagocytic activity of macrophages newly generated from the nonadherent cell fraction was relatively weak, but it was activated during further incubation. Based on these results, the maturation process of macrophages can be divided into at least the following four stages; glass‐nonadherent nonphagocytic precursor cells, glass‐adherent nonphagocytic precursor cells, immature macrophages with low phagocytic activity, and mature macrophages with full phagocytic activity. The addition of the capsular polysaccharide of Klebsiella pneumoniae (CPS‐K) to cultures of spleen cells markedly suppressed the generation of macrophages. The suppressive effect of CPS‐K depended on its dosage, and the minimum concentration of CPS‐K showing a definite effect was 0.05 μg/ml. CPS‐K inhibited further generation of macrophages in either the nonadherent or adherent cell fraction at any time after the start of the culture. The suppressive effect of CPS‐K on the generation of macrophages could not be reversed by simple washing of spleen cells which had been kept in contact with CPS‐K for 3 hr. There was no evidence which showed that CPS‐K exhibited direct cytotoxic effects on spleen cells in the culture.