In vitro and in vivo activity of polyclonal and monoclonal human immunoglobulins G, M, and A against Pseudomonas aeruginosa lipopolysaccharide.

We evaluated the in vitro opsonophagocytic killing activity of monoclonal human immunoglobulin G (IgG), IgM, and IgA specific for Pseudomonas aeruginosa lipopolysaccharide and the in vivo protective capacity in neutropenic mice of both monoclonal and purified polyclonal IgG, IgM, and IgA. Monoclonal IgM was efficacious in mediating opsonophagocytic killing only in conjunction with complement, whereas monoclonal IgG opsonic killing was potentiated by complement, and monoclonal IgA opsonic killing was independent of complement. These findings are similar to those previously reported for purified polyclonal IgM, IgG, and IgA. The monoclonal and polyclonal immunoglobulins had comparable 50% protective doses in neutropenic mice (range, 0.28 to 0.46 microgram per mouse). The protective activity of IgM in neutropenic mice was abolished by cobra venom factor treatment, whereas IgG and IgA maintained efficacy in cobra venom factor-treated mice. These data indicate that all three major human serum immunoglobulin isotypes have opsonophagocytic and protective activities against P. aeruginosa, with a critical role for complement in the function of IgM.