Binding of soluble immune complexes to Fc receptors on human neutrophils--detection by double-coating indirect rosette formation.

By using double-coating indirect rosette formation (DIRF), which is a modification of Coomb's mixed antiglobulin reaction, soluble immune complexes of ferritin (Fer) and rabbit anti-Fer in 40- to 120-fold antigen excess are shown to bind to the Fc receptor (FcR) on human neutrophils and lymphocytes. The molar ratios of anti-Fer antibody and Fer in these immune complexes are determined, at least, 1:7 and 1:21 respectively. These immune complexes have the same capabilities in detecting FcR-bearing neutrophils and lymphocytes, which is dependent upon the amounts of anti-Fer antibody present in the complexes. 81% on average of human neutrophils bear FcR which is trypsin resistant. The FcR on neutrophils is partially sensitive to pronase and completely inactivated after short glutaraldehyde fixation at 0 degrees C of the cells. Our findings strongly suggest that the weak binding of soluble immune complexes in antigen excess in some studies reflected the limitation of techniques employed to detect the binding rather than the nature of FcR on phagocytes.