Contribution of humoral and cellular factors to the resistance to experimental infection by Pseudomonas aeruginosa in mice. II. Opsonic, agglutinative, and protective capacities of immunoglobulin G anti-Pseudomonas antibodies.

The opsonic, agglutinative, and mouse protective capacities of anti-Pseudomonas antibodies in immune and normal human immunoglobulin G (IgG) preparations were investigated. Opsonic activities of the immune IgG preparations correlated well with their protective activities. Antibodies present in normal IgG showed a substantial agglutinative activity but were poorly protective. Anti-Pseudomonas antibodies of both normal and immune IgG preparations were directed against the same serotype antigen as demonstrated by absorption experiments. Immune anti-Pseudomonas IgG antibodies fixed complement very efficiently as demonstrated by opsonophagocytic and hemolytic tests. Natural anti-Pseudomonas IgG antibodies fixed complement very poorly although they promoted phagocytic killing of bacteria only in the presence of heat-labile serum factors. It was concluded that, although agglutination can be used for qualitative measurement of antibacterial antibodies, it fails to measure their functional capacities.