Reduction of circulating granulocytes induced by type 1 pneumococcal cell walls in New Zealand white rabbits

Abstract

Granulocytopenia seen during human pneumococcal disease is associated with a worsened prognosis. Streptococcus pneumoniae type 1 reduces circulating granulocytes and induces pulmonary leukostasis in rabbits. We studied which type 1 pneumococcal fraction(s) might be responsible for the reduction in circulating granulocytes. Rabbits were challenged intravenously with nonpyrogenic sterile saline, sonicated type 1 pneumococci, capsular polysaccharide from type 1 pneumococci, or cell walls from type 1 pneumococci. Nonviable pneumococci caused a mean decrease in blood granulocytes of 64% as compared with a mean increase of 124% in saline-injected controls, a difference significant at P less than 0.001. Pneumococcal cell walls induced significant decreases in circulating granulocytes at all doses tested when compared with saline-injected controls, whereas capsular polysaccharide induced no reduction in granulocytes. On a weight-for-weight basis, cell wall induced significantly more granulocyte reduction than did capsular polysaccharide at doses of either 10 mg (P less than 0.01) or 20 mg (P less than 0.005). A nonencapsulated pneumococcus also induced a profound granulocyte reduction (mean decrease in blood granulocytes, 88%) in the absence of detectable circulating polysaccharide. The cell wall fraction of S. pneumoniae type 1 was a more effective constituent in promoting the reduction in circulating granulocytes in rabbits.