Pili as a mediator of the attachment of gonococci to human erythrocytes

Isolated pure gonococcal pili were found capable of producing direct agglutination of human erythrocytes. Four different strains of gonococci were compared, and hemagglutination was produced by isolated pili or piliated gonococci but not by nonpiliated gonococci of each strain. Pili from each of the four strains were antigenically distinguishable using antisera specific for pili to agglutinate piliated gonococci, form precipitin lines in Ouchterlony immunodiffusion, or inhibit hemagglutination caused by purified pili or piliated gonococci. However, these tests also demonstrate some shared antigenicity among pili. Shared antigens among the four pili types were quantitated at less than or equal to 2.5% by radioimmunoassay. Inhibition of hemagglutination was most marked with antiserum to the homologous pili type. Inhibition of hemagglutination by antiserum to heterologous pili suggested that shared antigens on pili from B and 2686 strains of gonococci are located near the erythrocyte attachment moiety of B strain pili and removed from the attachment moiety of 2686 strain pili. These results suggest that antigenic heterogeneity of pili will prove an important factor in any efforts to use pili as a vaccine for gonorrhea.