Immunoprotective activity of capsular polysaccharide in Klebsiella pneumoniae ribosomal preparations does not involve ribonucleic acid.

Two peaks were obtained by cesium chloride density gradient ultracentrifugation of Klebsiella pneumoniae ribosomal preparations. Peak I contained capsular polysaccharide, lipopolysaccharide, protein, and less than 0.5% ribonucleic acid. Peak II consisted mainly of ribonucleic acid, with low amounts of protein and capsular polysaccharide. Expressed as capsular polysaccharide content, the 50% protective dose of peak I and of nonfractionated ribosomal preparations was nearly constant (2.6 and 1.2 ng, respectively). Since peak I contained less than 0.5% ribonucleic acid, these results provide evidence that ribosomal ribonucleic acid is not required for protection of mice by K. pneumoniae capsular polysaccharide which contaminates ribosomal preparations.