Clearance of red cells by monoclonal IgG3 anti-D in vivo is affected by the VF polymorphism of Fcγ RIIIa (CD16)

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SUMMARYHuman red cells (RBC) coated with IgG anti-D are cleared from the circulation to the spleen by macrophages which express IgG receptors (Fcγ R). Polymorphisms of Fcγ RIIa and Fcγ RIIIa affect IgG binding in vitro, and may alter the efficiency of clearance of immune complexes in vivo. In a RBC clearance study, 22 Rh D-negative subjects were given 100–400 μg human monoclonal or polyclonal IgG anti-D i.m. followed 48 h later by 51Cr-labelled D+ RBC. The half lives of the infused D+ RBC were determined, together with the coating levels of anti-D on the D+ RBC. Fcγ RIIA and FcγRIIIA genotyping was performed. Large ranges of phagocytosis and extracellular lysis of RBC in vitro, and of half lives of RBC in vivo, were observed. Clearance of RBC coated with monoclonal IgG3 anti-D (BRAD-3) was more rapid in five subjects homozygous for Fcγ RIIIa-F/F158 than in three subjects expressing the Fcγ RIIIa-V158 allele (P = 0·024). This effect was not observed, however, for those individuals given polyclonal anti-D. There was also no significant difference in the efficiency of RBC destruction in vitro or of RBC clearance in vivo between the subjects analysed for individual genotypes or alleles or combinations of alleles. In conclusion, the presence of the Fcγ RIIIa-V158 allele compromised the efficiency of removal of RBC coated with IgG3 anti-D.

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