Quantitative Determination, in Type-specific Antisera to Hemophilus Influenzae, of the Antibody That Cross-reacts with Encapsulated Pneumococci.

In 1942 Chapman and Osborne reported the first of a series of serological cross reactions involving the type-specific polysaccharides of Diplococcus pneumoniae and Hemophilus influenzae. Since then D. pneumoniae of types VI, XVA, XXIX, and XXXVB (Neter, 1943; Zepp and Hodes, 1943; Alexander, Leidy, and MacPherson, 1946) have been found to show capsular swelling in the presence of type b H. influenzae antibody, and D. pneumoniae type VIB and type XI were found to cross-react with type a (Chapman and Osborne, 1942) and type c (Alexander, Leidy, and MacPherson, 1946) H. influenzae antibodies, respectively. When the pleomorphism of H. influenzae is borne in mind, it is evident that the cross reactions described could lead to serious errors in the immediate identification by capsular swelling of any of the foregoing types of pneumococci or influenza bacilli involved. It was therefore considered desirable to measure in absolute terms the relative amounts of cross-reacting antibodies contained in rabbit antisera that had been produced in this laboratory against different strains of types a, b, and c H. influenzae. If the available sera were found to differ in this respect, such information would be useful as a guide to the selection of strains to be used for the preparation of diagnostic sera, the strain of choice being one that engendered the minimuim response of cross-reacting antibodies.