Immunization of Rabbits with Type II Pneumococcal Polysaccharide.

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Abstract
A prepn. of type II pneumococcal polysaccharide known to contain 0.42% N was found to be antigenic in rabbits. Rabbits that had received intra-dermal or intraven. injn. with minute amts. of the polysaccharide developed an active resistance to interdermal infection with pneumococcus type II. The pooled serum secured from animals that had been given 40 [mu]g. of polysaccharide intradermally offered mice passive protection against at least 10,000 L. D. of pneumococcus type II, but not against a single L. D. of type I. The pooled serum secured from rabbits that had received intracut. a total of 70 [mu]g. of the polysaccharide offered mice protection against almost 10,000 L. D. of the homologous organism. The mouse-protective sera failed to precipitate with a soln. of the type-specific polysaccharide or to agglutinate with encapsulated pneumococcus type II that had been killed with formalin and heat. In no case did the sera secured from the exptl. animals previous to immunization with the polysaccharide offer mice passive protection against pneumococcus type II or I. It is suggested that the previous failures to immunize rabbits with the type-specific polysaccharides may be attributed to "immunological paralysis" resulting from the use of excess polysaccharide. The evidence indicates that the mouse-protective antibody is the specific anti-carbohydrate which occurs in amts. too small to be detected by quantitative precipitin technics. An attempt to demonstrate univalency of the type-specific mouse-protective antibody failed.