Inhibition of whole blood antibody dependent cellular cytotoxicity by heat aggregated human IgG.

Inhibition of the whole blood antibody dependent cellular cytotoxicity (ADCC) of a lymphoblastoid cell line by heat aggregated human IgG (HAI) is described. Optimal sensitising antibody and effector cell concentrations were established to permit the detection of 0.1 microgram/ml HAI. Conditions which avoid the ADCC inhibitory effects of normal human sera were defined. Twelve paired normal human sera were stored at -70 degrees C for prolonged (greater than 3 years) and shorter (less than 6 months) periods of time. Sensitised sheep red cells were used to determine complement depletion in serum dilutions heated at 40 degrees C, 45 degrees C, 50 degrees C. Concentrations of human IgG (1 000-0.1 microgram/ml) were prepared in foetal calf serum before heating at 63 degrees C for 30 min to aggregate the IgG. ADCC inhibitory activity, frequently characteristic of normal human serum was minimised (less than 10%) when sera were stored at -70 degrees C and heated to 50 degrees C for 30 min to inactivate serum complement. This assay provides an economical, reproducible and sensitive test for the detection of circulating IgG complexes.