ROLE OF FC-GAMMA-RIIA (CD32) IN IGG ANTI-RHD-MEDIATED RED-CELL PHAGOCYTOSIS IN-VITRO

To test the role of Fc gamma RIIa in IgG anti-RhD-mediated phagocytosi s three IgG1 and two IgG3 human monoclonal anti-D antibodies were test ed for ability to mediate binding/phagocytosis of cDE/cde and -D-/-D- red cells by Fc gamma RIIa-R131 and Fc gamma RIIa-H131 cDNA-transfecte d 3T6 fibroblasts. Both IgG3 monoclonal antibodies brought about -D-/- D- cell interaction with IIa-transfected fibroblasts, while only one o f them, Og3, mediated binding of cDE/cde targets. Although Fc gamma RI Ia expression was three times greater on IIa-R131 than on IIa-H131 fib roblasts, the latter bound significantly more Og3-coated cDE/cde- and IgG3 anti-D-sensitized -D-/-D- cells, respectively, than the former ef fecters and showed some phagocytosis of the -D-/-D- targets. IgG1 anti -D antibodies were inactive in mediating red cell interaction with the fibroblasts. Moreover, monoclonal anti-Fc gamma RII IV.3 partially in hibited the phagocytosis by adult or fetal monocytes of Og3-sensitized cDE/cde cells. Fc gamma RIIa-H/H131 monocytes exhibited higher phagoc ytic indices towards these targets than monocytes of other IIa allotyp es. The results indicate that Fc gamma RIIa can participate in the pha gocytosis of red cells coated with IgG3 anti-D; in this case the allot ype of the receptor will modify the extent of red cell destruction.