Direct evidence for the involvement of capsular polysaccharide in the immunoprotective activity of Klebsiella pneumoniae ribosomal preparations.

Previous work has demonstrated the capsular serotypic specificity of the protection conferred on mice by Klebsiella pneumoniae ribosomal preparations. The data in these studies support the hypothesis that capsular polysaccharide plays at least some role in the specificity of the protection conferred by ribosomal preparations. In this investigation, the presence of capsular polysaccharide and lipopolysaccharide in K. pneumoniae ribosomal preparations was demonstrated by using immunodiffusion tests. Lipopolysaccharide content was determined for mice treated with actinomycin D. The serotype of O antigen did not play a role in the orientation of the specificity of the protection. The possibility that lipopolysaccharide might act as an adjuvant was not unlikely since the ribosomal preparations which contained the greatest amounts of lipopolysaccharide appeared to be the most immunoprotective preparations. Ribosomal preparations extracted from a noncapsulated mutant of K. pneumoniae did not protect mice. This finding suggested that capsular polysaccharide might play a role in the immunoprotective activity of ribosomes. This hypothesis was tested by using K. pneumoniae K2 bacteriophage-associated-glycanase, which specifically hydrolyzed K. pneumoniae K2 capsular polysaccharide and thereby suppressed the immunoprotective activity of K. pneumoniae K2 ribosomal preparations. In contrast, the K2 bacteriophage-associated glycanase did not interfere with the immunoprotective activity of K. pneumoniae K1 ribosomal preparations. These results clearly demonstrate that capsular polysaccharide, which is an extraribosomal antigen, is involved in the immunoprotective activity of K. pneumoniae ribosomal preparations.