Precipitating cross-reactions among pneumococcal types.

Data accumulated over many years are brought together on cross-reactions of 46 among the more than 80 pneumococcal serological types, with the idea of correlating cross-reactions with the structures of the relevant type-specific capsular polysaccharides, insofar as these have been determined. The precipitin reaction was carried out with the polysaccharides and antibodies raised in horses, rabbits, and a mule. Quantitative values (micrograms of antibody nitrogen per milliliter of antiserum at 0 to 1 degree C) are given in many instances and discussed, together with arbitrary qualitative data, in terms of the known structures of the polysaccharides. Some precise relationships are uncovered, and an attempt is made to determine why some of the cross-reactions are reciprocal and why others are only unilateral.