Antigenic potency of cell-free extracts of leptospires

Virtually all of the leptospiral cell's antigenic principle which is reactive in the complement fixation test with hyperimmune rabbit serum has been isolated in two cell-free polysaccharide-containing preparations. This investigation has been restricted to the study of antigenic potency in vivo in rabbits of aqueous (Fraction 1) and alcoholic (Fraction 2) cellfree extracts of Leptospira bataviae and Leptospira icterohaemorrhagiae AB (Wijnberg). Fraction 1 has been found to be immunogenic as well as antigenic, as determined by antibody formation (complement-fixing antibodies and agglutinins) upon intravenous injection into rabbits. The experiments have disclosed that Fraction 1 preparations comprise two immunologically distinct antigens namely, a genus specific complement-fixing principle and a serogroup specific agglutinogen. A second polysaccharide-containing preparation, Fraction 2, reacts as a partial antigen or haptene. The antibodies of homologous hyperimmune serum react very well in the complement fixation test with the latter antigen and are sharply species specific. The antibodies are either quantitatively reduced or lacking in homologous antifraction 1 and 2 serums and in heterologous hyperimmune serums of two other serotypes of leptospires. The limited data obtained suggest that two chemically distinguishable polysaccharide-containing preparations of the leptospiral cell comprise independent complement-fixing antigen systems. A possible practical application of Fraction 1 preparations in improving diagnostic services and in distinguishing serotypes of leptospires is discussed.