Effect of Capsular Polysaccharide of Klebsiella pneumoniae on Host Resistance to Bacterial Infections

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Abstract
In normal mice, the total count of peritoneal leukocytes was markedly decreased after intraperitoneal (i.p.) injection of the capsular polysaccharide of Klebsiella pneumoniae (CPS‐K) depending on the dosage injected. This decrease was mainly due to the depletion of macrophages, and a decrease in the number of lymphocytes occurred to a lesser extent. CPS‐K in relatively smaller doses mobilized polymorphonuclear neutrophilic leukocytes (PMN) into the peritoneal fluid but it decreased them transiently in larger doses. In mice infected i.p. with a virulent strain of Salmonella enteritidis, there was an abundant emigration of PMN into the peritoneal fluid. When 200 μg of CPS‐K was injected i.p. immediately before bacterial challenge, emigration of PMN was markedly delayed for 48 hr after infection. Associated with this suppressed emigration of PMN, the numbers of macrophages and lymphocytes in the peritoneal fluid were significantly less in mice treated with CPS‐K than those in untreated control mice for 48 hr after infection. The numbers of both cell‐associated and extracellular bacteria in the peritoneal fluid were markedly greater in mice treated with CPS‐K than those in untreated control mice. In both in vivo and in vitro experiments, ingestion of bacteria by macrophages and PMN was not blocked by CPS‐K or neutral CPS‐K, the active substance responsible for the infection‐promoting effect of CPS‐K. It appeared that CPS‐K somehow impaired the intraphagocytic bactericidal activity.