Immunological Basis of Serum Resistance of Neisseria gonorrhoeae

Abstract

The immunological basis for resistance of certain strains of N. gonorrhoeae to the bactericidal action of normal human serum was studied by investigating the potential role of factors which are known to interfere with each of the sequential steps that result in immune lysis of gram-negative bacteria. Strains of N. gonorrhoeae were characterized as serum-sensitive (sers) or serum-resistant (serr) on the basis of their sensitivity to lysis by the sera of 6 normal individuals. Neither intrinsic resistance to the lytic action of activated human complement nor inaccessibility of the cell membrane to C5b [complement component 5 fragment b] accounted for serr. Outer membrane lipopolysaccharide (LPS) was the target antigen for lytic antibody in normal human sera. The gross chemical composition and molecular size of the LPS of the strains were heterogeneous and no consistent patterns of differences between those extracted from serr and from sers strains were found. Neither IgA nor IgG blocking antibody in normal human serum was responsible for serr. Evidently, serr results from the absence from the LPS of the strains of antigenic loci for the lytic antibody in most normal human sera, or, expressed as a function of the host, tbe absence from the sera of most normal humans of lytic antibody directed against LPS antigenic loci for immune lysis.