The detection of circulating immune complexes in normal subjects using four different methods.

336 estimations of circulating immune complexes have been performed on the sera of blood donors by four different methods: the solid phase C1q binding test, the fluid phase C1q binding assay, the conglutinin binding test and the Raji cell radio-immune assay. Between 68 and 105 subjects were used in the analysis of each method. With the first three methods, immune complex levels showed a peaked asymmetric distribution with a positive tail including about 10% of subjects, whereas using the fourth method immune complex values were widely spread. No difference in immune complex values between males and females was found. There was a significant trend for the prevalence of immune complexes to increase with age when methods were used which detect complexes through C3 binding. In a further 13 subjects tested at regular intervals during a period of 24 hours, using the fluid phase C1q binding test, significant variations in immune complex levels were found but no consistent pattern of variation at different hours of the day or after meals could be seen. In studies of immune complexes on small groups of patients it is advisable to test multiple samples from te same subjects taken at different times, whereas when large series of patients are being studied results should be compared to those obtained with age matched controls.