Murine Immunoprotective Activity of Klebsiella pneumoniae Cell Surface Preparations: Comparative Study with Ribosomal Preparations

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Abstract
Cell surface preparations and ribosomal preparations were extracted from K. pneumoniae. Agar gel diffusion with antisera to cell surface preparations or ribosomal preparations indicated common antigenic components among the preparations. Lipopolysaccharide and capsular polysaccharide were identified in the cell surface preparations. These results and the previous identification of lipopolysaccharide and capsular polysaccharide in ribosomal preparations suggest that these antigens are responsible for the immunochemical cross-reactivity observed among these 2 bacterial extracts. Active protection could be induced in mice by these 2 preparations. On a dry-weight basis, cell surface preparations provided better immunoprotective activity than did ribosomal preparations. The 50% protective dose of both preparations is practically the same on the basis of their capsular polysaccharide content. The immunoprotective moiety of ribosomal preparations is apparently the contaminating cell surface antigens. The low level of nucleotidic components detected in purified cell surface preparations led to the inference that the immunoprotective activity of capsular polysaccharide may not be dependent on the adjuvant activity of RNA. The involvement of capsular polysaccharide in the immunoprotective capacity of cell surface preparations is demonstrated by using a degradation of this antigen by K. pneumoniae bacteriophage K2-associated glycanase or by using a preparation extracted from a noncapsulated mutant of K. pneumoniae. The low protective ability of purified capsular polysaccharides is in contrast to its greater activity when induced in bacterial cell surface preparations. The protective activity of K. pneumoniae capsular polysaccharide may be dependent on its association with other surface antigenic components present in cell surface preparations or may be dependent on its native form in the bacterial cell surface.