Studies on the antigenic variation of pili and outer membrane proteins from Neisseria gonorrhoeae

Abstract

Rabbits were immunised with outer membranes from colonial opacity variants of Neisseria gonorrhoeae P9 and antibodies were detected by an enzyme-linked immunosorbent assay (ELISA). ELISA-inhibition experiments with purified antigens revealed approximately equal proportions of antibodies directed against each of the three major surface antigens: lipopolysaccharide, protein I and protein II. Inhibition experiments with intact gonococci showed considerable surface antigenic diversity which correlated with differences between the molecular species of protein II present. Proteins II from colonial variants of the same strain showed little cross-reactivity with specific anti-protein II sera, demonstrating antigenic variation in *he surface exposed region of the protein.

Gonococci were cultured from the urethra of male patients and from the cervix and urethra of female contacts. Isolates from within a patient group were of the same strain, but showed differences in molecular weight of protein II and pili. Radioimmune precipitation assay showed that most patients produced serum antibodies directed against protein I. Anti pilus antibodies, when present, showed cross-reactivity wiyh pili from homologous and heterologous strains. Antibodies to protein II were found to be highly specific. These data suggest that the host immune response may be an important factor in causing antigenic shift during infection. Several sera also contained antibodies to a common surface protein of 43,000 molecular weight present in all strains tested.

Sera from patients convalescing from meningococcal infections had antibodies to the main outer membrane proteins which cross-reacted with gonococcal protein I and the 43,000 molecular weight protein. Anti-meningococcal protein II antibodies were highly specific. Strains of Dilated meningococci could be divided into two groups on the basis of antigenicity and sub-unit molecular weight. Strains from group 1 reacted with monoclonal antibodies directed against gonococcal pili, had pili with sub-unit molecular weight similar to that of gonococci, and could be detected by radioimmune precipitation or electroblotting. Strains from group 2 failed to react with the monoclonal antibodies, had pili with lower sub-unit molecular weight and could only be detected by radioimmune precipitation using polyclonal anti-pilus antiserum but not by electroblotting.

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