hFcγRIa internalization and modulation. (A) Internalization of ¹²⁵I-labeled rabbit IgG-ovalbumin complexes in IIA1.6 cells expressing hFcγRIa WT/γ-chain, hFcγRIa WT/mock vector, or hFcγRIa ▵315/γY65F,Y76F.¹²⁵I-labeled complexes were prebound at 4°C and internalization at 37°C was determined as described in Materials and Methods. No detectable binding/internalization was observed in nontransfected IIA1.6 cells (n = 3). (B) Modulation of hFcγRIa expression by rabbit IgG-ovalbumin complexes. Transfectants were incubated overnight with complexes as detailed in Materials and Methods. Receptor expression was determined using CD64-specific MoAb 32.2 and PE-labeled goat antimouse IgG1. The percentage of modulation was calculated as defined in Materials and Methods (n = 3). Error bars indicate standard errors of the mean.