The EA-rosette inhibition assay as a test for immune complexes

Abstract Soluble transferrin-anti-transferrin (TAT) complexes were shown by EA-rosette inhibition assay to block human lymphocyte receptors for the Fc of reacted IgG (Fcγ) in vitro. These complexes, which provide a convenient and controlled source of Fcγ receptor blocking material, were found to inhibit EA-rosette formation over a wide range of antigen: antibody ratios. Complexes were detected at both 37°C and 4°C although the range and sensitivity of the assay was markedly increased at 4°C. The inhibitory capacity of TAT complexes was lost on pre-incubation with normal human serum suggesting that only non-complement fixing complexes are detected by EA-rosette inhibition. ‘False positive’ inhibition by antilymphocyte antibodies occurs at 37°C but not at 4°C. Partial automation of the assay was achieved by calibrating a Coulter counter for rosette counting, thus obviating the requirement for tedious and subjective microscopic determinations.