A PROTEIN ANTIGEN CHARACTERISTIC OF BRANHAMELLA CATARRHALIS. Serological Identification of the Genus

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Abstract
Precipitation patterns of sonicated, acid-extracted and other extracts from B. catarrhalis were examined by double diffusion-in-gel, using antiserum to B. catarrhalis. Acid extract gave rise to 4 distinct precipitates. One ofthese lines was further studied. The bacterial component responsible for this line was trypsin-sensitive, indicating that it was a protein. It was anodally localized by crossed immunoelectrophoresis. By absorption of antiserum with whole bacteria, the precipitating capacity of the serum was diminished, suggesting that the protein antigen (P-antigen) was exposed on the bacterial surface. F(ab'')2-fragments of IgG from antiserum, but not from normal rabbit serum, precipitated the P-antigen, indicating that it was a true antigen-antibody reaction. It was possible to make an IgG preparation monospecific for the P-antigen by absorbing antiserum with trypsinized bacterial extract. Strains (31) of B. catarrhalis, 9 strains of Neisseria gonorrhoeae, 10 strains of N. meningitidis, 12 other Neisseria spp. and 2 strains of Haemuphilus influenzae were investigated for presence of cros-reacting surface antigens, using IgG monospecific for the P-antigen and 125I-labeled protein A from Staphylococcus aureus. After antibody exposure, all 31 strains of B. catarrhalis showed abundant uptake of protein A. No significant uptake was detected on any other investigated strain. The P-antigen appears to be characteristic of B. catarrhalis. The possibility of a serological identification of the species is introduced. Precipitating antibodies against the P-antigen were demonstrated in 69% of normal human sera.