The ER-rosette inhibition assay as a test for immune complexes.

Soluble transferrin-anti-transferrin (TAT) complexes were shown by EA-rosette inhibition assay to block human lymphocyte receptors for the Fc of reacted IgG (Fc gamma) in vitro. These complexes, which provide a convenient and controlled source of Fc gamma receptor blocking material, were found to inhibit EA-rosette formation over a wide range of antigen: antibody ratios. Complexes were detected at both 37 degrees C and 4 degrees C although the range and sensitivity of the assay was markedly increased at 4 degrees 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 degrees C but not at 4 degrees 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.