OPSONOPHAGOCYTIC ACTIVITY-INDUCED BY CHIMERIC ANTIBODIES OF THE 4 HUMAN-IGG SUBCLASSES WITH OR WITHOUT HELP FROM COMPLEMENT

The opsonophagocytic activity of the four human IgG subclasses was stu died using chimeric mouse-human antibodies with specificity for the ha pten NIP. As target cells we used haptenized sheep red blood cells and N. meningitidis, labelled with different amounts of hapten. We used p olymorphonuclear leucocytes (PMN) as effector cells to measure respira tory burst (RB), and U937 to measure phagocytosis/rosette formation. W hen the target cells were opsonized with antibody only, and PMN used a s effector cells, IgG3 was highly efficient, while IgG1 revealed an in termediate activity and IgG2 and IgG4 were negative. The same pattern among the subclasses was obtained in the presence of complement source , when target cells with low hapten concentration were used. However, at high epitope concentration on the target cells, in the presence of complement source, IgG2 was highly active, while IgG4 was still negati ve or only slightly positive. When U937 were used as effector cells an d complement was omitted, IgG1, IgG3 and IgG4 all revealed high phagoc ytic/rosette-forming activity, while IgG2 was negative. When the targe t cells were opsonized with antibody and complement, the phagocytic/ro sette-forming activity was often suppressed. Our results reveal that a ll four human IgG subclasses possess opsonophagocytic capacity, but wi th different requirements concerning complement and Fc gamma Rs. They also enlighten us as to how IgG2 might perform its protective effect a gainst harmful bacteria displaying high density of carbohydrate epitop es on their outside surface.