Activation of complement by serum-resistant Neisseria gonorrhoeae. Assembly of the membrane attack complex without subsequent cell death.

Abstract

Interaction of the human complement system in normal human serum (NHS) with serum-resistant and -sensitive Neisseria gonorrhoeae was evaluated to better understand the mechanism of serum-resistance. Complement activity (CH50) was depleted from NHS in a dose-dependent fashion by both serum-resistant and -sensitive N. gonorrhoeae. No detectable CH50 remained in NHS incubated with 10(9) colony-forming units (CFU)/ml serum of either resistant or sensitive strains. When smaller numbers of bacteria were incubated with NHS, lesser, yet comparable, amounts of CH50 were depleted by both resistant and sensitive strains. Hemolytic C2 activity was diminished by 33% in the case of resistant N. gonorrhoeae (10(8) CFU/ml serum) and by 48% in the case of a sensitive strain. No detectable decreases in hemolytic C4 or C7 activities were found with either sensitive or resistant strains at this concentration. Both resistant and sensitive strains activated C1s in NHS. Resistant strains specifically activated 19-21% of radiolabeled C1s in NHS, whereas sensitive strains activated 18-32%. Both resistant and sensitive strains also activated C5 in NHS. In binding assays using radiolabeled C5 and C9 in NHS, resistant and sensitive strains bound comparable amounts of C5 and C9. The number of bound C5 and C9 molecules varied according to the number of bacteria or amount of serum used in the assay. The ratio of C9/C5 bound to a sensitive strain was 6.8, and to a resistant strain was 8.2, suggesting that C5 and C9 were incorporated into membrane attack complexes (MAC). Electron microscopic examination of resistant and sensitive strains incubated with NHS revealed that MAC is bound to the surfaces of the resistant strain as well as the sensitive strain.

Pathogenesis of Campylobacter fetus infections. Failure of encapsulated Campylobacter fetus to bind C3b explains serum and phagocytosis resistance.

“…Alternatively, the capsule may preclude covalent attachment of C3 to the bacterial surface which would not permit amplification by the alternative pathway (33). In any event, the mechanism ofserum-resistance of encapsulated C. fetus appears to be novel and differs from those described for smooth Enterobacteriaceae (15), or serum-resistant gonococci (34,35). For those organisms, C3 binding and C5b-9 generation are efficient, but for a variety of reasons (18, 34) the terminal membrane attack complex fails to insert into vital cell membrane structures.…”

Molecular basis for serum resistance in Neisseria gonorrhoeae

“…MACs (or C5b-9) form on the surfaces of both serumsensitive and serum-resistant organisms (22,27). Both sensitive and resistant strains consume equivalent amounts of C9 and bind similar numbers of C7 and C9 molecules when incubated in NHS (22,27).…”

“…In addition, (iii) blocking antibodies, directed at outer membrane protein antigens, modulate or down-regulate bacterial killing, mainly by preventing binding of bactericidal antibodies to lytic epitopes (26,49). Finally, and least well understood, (iv) there is a partial failure to form the C5 convertase necessary for full development of membrane attack complexes (MACs or C5b-9 [11, 12]) but also a failure of MACs that do form to fully insert through the gonococcal outer membrane (22,27). In addition, less C3 may bind to serum-resistant organisms, and C3 that does bind may not be hemolytically active (51).…”

Mechanism of resistance to complement-mediated killing of bacteria encoded by the Salmonella typhimurium virulence plasmid gene rck.

“…Stable binding of the MAC to the bacterial membrane without lysis or death has been reported with certain serum-resistant strains of Neisseria gonorrhoeae (39,48,49). Joiner et al (39) found evidence that nonbactericidal C5b-9 was associated with bacterial outer membrane constituents, was trypsin sensitive, and ran on sucrose density gradients as complexes of higher molecular weight than did the bactericidal MAC formed on the serum sensitive strain.…”

“…5 A) most likely represents terminal C5b-9 complexes containing multiple molecules of C9, since at least three molecules of C9 are necessary for formation of SDS-resistant tubular polyC9 (50). High molecular weight MACs are generally heterogenous, containing both SDS-resistant tubular polyC9 and linear C9 that is broken down to monomeric C9 by SDS under reducing conditions (49); both populations are seen in the SDS-PAGE of peak A (Fig. 6, lane 1).…”