Outer-membrane protein and lipopolysaccharide serotyping of Neisseria meningitidis by inhibition of a solid-phase radioimmunoassay.

A new procedure involving inhibition of a solid-phase radioimmunoassay was developed for specific determination of the outer-membrane protein and the lipopolysaccharide (LPS) serotypes of meningococci. Antigen was allowed to bind to the wells of a polyvinyl microtiter plate and then reacted with a limiting amount of homologous antibody which had been preincubated with buffer or a standard concentration of inhibiting antigen. The amount of antibody bound per well was quantitated by incubation with excess 125I-labeled goat anti-rabbit immunoglobulin. Typing sera for detecting eight LPS antigens and 18 protein antigens were made in rabbits by use of both the group C and group B bactericidal serotyping strains. Reactions between unabsorbed sera and purified LPS were inhibited in the LPS typing system, whereas reactions between absorbed sera and outer-membrane complex were inhibited in the protein typing system. Outer-membrane complex was used as the inhibiting antigen in both cases. Approximately 97% of the 80 group B and C strains tested were LPS typable, and 80% were protein typable. Of 51 group A strains tested, however, only 22% were LPS typable and 14% were protein typable. Several nonreciprocal correlations between the occurrence of particular LPS and protein serotype antigens on the same strain were observed, but in general the protein and LPS serotype antigens appeared to occur independently.