Activation of Murine Peritoneal Macrophages by Streptococcus pneumoniae Type II Capsular Polysaccharide: Involvement of CD14-Dependent Pathway

In this study we examined the ability of capsular polysaccharide type 2 (PS) from Streptococcus pnemoniae to induce secretory and cellular responses in peritoneal macrophages. Tumour cytotoxicity induced by preincubation with PS was demonstrated to be concentration-dependent. PS-induced tumouricidal activity was partially abrogated by anti-tumour necrosis factor (TNF)-α and inhibitor of nitric oxide, whereas anti-interferon (IFN)-α/β antibody and the scavengers of reactive oxygen intermediates had no effect. In addition, supernatants from macrophages treated with PS contained TNF-α, and their iNOS-enzymatic activity was significantly increased. Thus, the tumouricidal activity induced by PS appeared to be mediated by the production of TNF-α and nitrite. Treatment of macrophages with PS increased the expression of CD14, the receptor for lipolysaccharide (LPS)/LPS-binding protein. Moreover, blocking antibody to CD14 abrogated partially TNF-α and nitrite induction by PS, suggesting that the PS-induced CD14 upregulation was correlated with secretion of TNF-α and nitrite. Taken together, these results demonstrate that PS may induce macrophage-secretory and cellular activities, in part, possibly via CD14-dependent pathway.