Physiological aspects of circulating immune complexes in the normal population.

Circulating immune complexes (CIC) have been investigated in 100 normal subjects; the RIA-Raji and the C1q-BA conventional methods, as well as a new solid phase microassay utilizing purified C1q and the systematic search of cryoprecipitates were employed. CIC serum levels did not differ in regards to sex; in relation to age, values for C1q-BA were identical in subjects from 0 to 60 years and also in those beyond age 60; the differences encountered by RIA-Raji or by the C1q-SP microassay in these two main groups were not statistically significant. Cryoprecipitates were present in 100% of the 68 examined subjects. Immunoglobulins (G, A and M), anti-nucleic acid (DNA and Poly A) and CIC (by the three methods) were present in the cryoprecipitates while lymphocytotoxins, rheumatoid factor and C3 were undetectable; protein content of the cryoprecipitates increased significantly with age, reaching a normal superior limit of 0.52 mg/ml beyond age 30. These findings further support the role played by CIC in normal immune response and may help in the understanding of the physiopathology of clinical conditions associated with immune complexes.