Lipids and Immunological Reactions Iii. Lipid Content of Specific Precipitates from Type I Antipneumococcus Sera

It has been reported (1, 2) that the presence of certain lipids is essential to the in vitro demonstration of type-specific agglutination and precipitation by antipneumococcus sera. I t was suggested that the antibody of antipneumococcus serum might be a phosphatideglobulin complex, the nature of the lipid fraction being dependent upon the species derivation of the antibody. Because of the minute amounts of phosphatide necessary to restore the in vitro properties of antisera from which lipids had been extracted, it was to be expected that the amount of lipid actually associated with the antibody itself would be very small. I t is apparent that if lipid does form a portion of the antipneumococcus antibody, much the simplest means of defining both its amount and character would be by a study of the antibody in an isolated and pure condition. Since, however, technical difficulties which interfere with the isolation of pure antibodies have not been entirely surmounted, it was necessary to study the antibody in its native state. While the method adopted has the disadvantages inherent to the chemical study of a substance dispersed in a complex system, these disadvantages are to some extent offset by the fact that the antibody had not been altered by chemical manipulation. Perhaps the most convenient and satisfactory means of obtaining a separation of the antibody from the various constituents of antipneumococcus sera is by precipitation with the homologous capsular polysaccharide. Such precipitates, if carefully prepared and washed by the method of Heidelberger and Kendall (3), afford adequate and readily available material for the quantitative study of those lipids associated with type-specific