Effector activating determinants on IgG. I. The distribution and factors influencing the display of complement, neutrophil and cytotoxic B-cell determinants on human IgG sub-classes.

It was possible to demonstrate complement fixation by IgG1 and IgG3 sub-class myeloma proteins which had been heat aggregated under standard conditions. Phagocytosis of bacteria by neutrophils was inhibited by IgG1, IgG2 and IgG3. Lysis of antibody-sensitized target cells by cytotoxic B lymphocytes was inhibited by all four sub-classes of IgG. IgG interacted with cytotoxic B lymphocytes, neutrophils and complement only after physical alteration. Cytotoxic B cell reacting activity was acquired during protein purification procedures and was only slightly increased by heating. Neutrophil inhibition activity appeared only after the IgG sub-classes were heated and aggregation had occurred. Very large aggregates, however, were inefficient inhibitory units. Complement fixation by IgG1 and IgG3 was markedly increased by heating and the largest aggregates showed greatest activity.