Antipneumococcal Cross Reactions of Antigens of Leuconostoc mesenteroides . ∗

Summary

1. The experiments dealt with the antipneumococcal cross reactions of non-dextran antigens of two strains of L. mesenteroides. The B512-F strain, which is commonly employed in manufacture of dextran plasma volume extenders, gave reciprocal cross reactions with type 27; the other strain gave reciprocal reactions with type 32 pneumococcus. The data proved that these immunological relationships depended upon similarities between the non-dextran antigens of the leuconostoc bacteria and the specific capsular polysaccharides (S) of the cross-reacting types (27 or 32) of pneumococci. 2. The type 27-reactive antigens of the B512-F strain were shown to be capsular constituents by Quellung reactions; this strain also liberated considerable amounts of the reactive material as a soluble substance into the fluids of broth cultures. The No. 6 strain failed to give Quellung reactions both with type 32 and its homologous antiserum, and appeared analogous in serological behavior to “intermediate” strains of pneumococci that have been described by others. 3. The possible use of antipneumococcal cross reactions as an aid in the differentiation of some strains of leuconostoc was suggested, and factors that underlie the serological diversity of the leuconostoc group were discussed.