Variable Region-Identical Monoclonal Antibodies of Different IgG Subclass Directed to Pseudomonas aeruginosa Lipopolysaccharide O-Specific Side Chain Function Differently

Abstract

Antibodies directed to polysaccharide (PS) antigens of bacteria are crucial to host immunity to infection. The isotypes of antibodies made to PS, however, are restricted primarily to IgM and IgG1 and IgG2 in man and to IgM and IgG3 in mice. Using sequential sublining and sib selection, an IgG1 murine monoclonal antibody that has variable regions identical to those of a parent IgG3 monoclonal antibody directed to the high-molecular-weight component of the O-specific side chain of Pseudomonas aeruginosa immunotype 1 lipopolysaccharide was derived. These antibodies differed markedly in their antigen binding and effector functions. IgG3 was superior in binding to multivalent PS both in purified and whole bacterial form, fixation of the third component of complement to the bacterial surface, and opsonization of P. aeruginosa for uptake by both murine and human phagocytes. These data suggest that the IgG subclass of these murine anti-LPS antibodies is an important determinant of both avidity for multivalent antigen and biologic function.

Human IgG2 Can Form Covalent Dimers

“…The ability of human IgG2 to dimerize and hence increase its avidity may represent an adaptation that permits more effective binding to the surfaces of bacteria and may help to more effectively trigger effector functions such as complement activation and Fc receptor binding. Such a mechanism has been suggested for mIgG3, which forms noncovalent polymers in the presence of Ag (12,13) and has been shown to be more effective at binding to a multivalent polysaccharide Ag and triggering complement activation and opsonization than a V region identical IgG1 (42). Anticarbohydrate IgGs in rats (43) and horses (37) have also been reported to have the propensity to form noncovalent aggregates; however, the nature of the IgG self-association in rats and horses has not been elucidated.…”

Clearance ofCitrobacter rodentiumRequires B Cells but Not Secretory Immunoglobulin A (IgA) or IgM Antibodies

“…Given that B cells were important for C. rodentium clearance but not secretory antibodies, we began to evaluate the role of IgG in antibacterial host defense. IgG3 antibodies are the predominant subclass of IgG antibodies that develop against bacterial cell wall polysaccharides after infections in mice, and this subclass shows the highest functional affinity over other isotypes for binding these bacterial structures (29,33). To test the role of IgG3 in host defense against C. rodentium, we used mutant mice that lack a key segment of FIG.…”

Binding to and Opsonophagocytic Activity of O-Antigen-Specific Monoclonal Antibodies against Encapsulated and NonencapsulatedKlebsiella pneumoniaeSerotype O1 Strains

“…With E. coli and P. aeruginosa, there have been differences in functional activity between the murine IgG subclasses, mostly at low antibody concentrations (30,36,38). There, IgG2a demonstrated the most pronounced bacterial killing activity second only to IgM (30).…”