Detection of circulating immune complexes: a new application of immune adherence haemagglutination.

A simple, rapid and economical method involving immune adherence haemagglutination (IAHA) has been developed for the measurement of circulating immune complexes (CIC) in human sera. Human D-positive erythrocytes with highly active C3b receptors were employed as indicator cells. The procedure can be completed within 2 h and with 25 microliters of serum. The lower limit of sensitivity of this IAHA method was 2 micrograms/ml of heat-aggregated IgG and 16 ng/ml of IgG as antigen in a complexed state with anti-IgG antibody. By applying this method, CIC were detected in sera from categories of patients in whom CIC have been reported with other methods. Studies thus far suggest that the IAHA method may be useful in detecting and quantifying CIC in the investigation of clinical syndromes in which these complexes are believed to relate to pathogenesis.