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 μg/ml HAI. Conditions which avoid the ADCC inhibitory effects of normal human sera were defined.Twelve paired normal human sera were stored at ?70°C for prolonged (> 3 years) and shorter (<6 months) periods of time. Sensitised sheep red cells were used to determine complement depletion in serum dilutions heated at 40°C, 45°C, 50°C and 56°C. Concentrations of human IgG (1 000–0.1 μg/ml) were prepared in foetal calf serum before heating at 63°C for 30 min to aggregate the IgG.ADCC inhibitory activity, frequently characteristic of normal human serum was minimised (<10%) when sera were stored at ?70°C and heated to 50°C for 30 min to inactivate serum complement. This assay provides an economical, reproducible and sensitive test for the detection of circulating IgG complexes.