IgA protease production as a characteristic distinguishing pathogenic from harmless neisseriaceae.

IgA proteases are extracellular enzymes of bacteria that have human immunoglobulin A of the IgA1 subclass as their only known substrate. The identification of this enzyme in neisseria prompted us to determine whether IgA protease production correlates with pathogenicity within this genus. Multiple clinical isolates of Neisseria gonorrhoeae, N. meningitidis and eight species of non-pathogenic neisseria that commonly colonize the normal human nasopharynx were examined for IgA protease activity. All N. gonorrhoeae and N. meningitidis strains were enzyme positive; all non-pathogenic strains were negative. Among meningococci, the enzyme occurred in strains carried harmlessly in the nasopharynx as well as those isolated from systemic infections. Because mucosal immune defense is largely mediated by antibodies of the IgA isotype, the finding that IgA protease activity is linked specifically to the pathogenic neisseria suggests that the enzyme may be involved in the pathogenesis of neisserial infection.