Evidence that the phagocytosis mediated by the peanut agglutinin-like activity of IgG(Fc) receptors of human monocytes is selectively modulated by estradiol and natural estrogens

The percentage of human monocytes (MCs) that are able to form rosettes with, and to phagocytose, IgG-coated sheep red blood cells (IgG-SRBCs) has been first determinedin vitro by a classical rosette assay in 12 postmen-opausal (PM) women. Half of them never received any suppletive estrogen (E) therapy at the time of testing, whereas the other six were chronically treated with E. Three different preparations of the same anti-SRBC IgG antibody batch were coated to SRBCs: the first one was the starting antibody preparation IgG(total] and the other two were purified by affinity chromatography either on Sepharose-concanavalin A (Con A) or on agarose-peanut agglutinin (PNA) columns specifically recognizing terminal, and/or accessible, -mannosyl IgG(Con A)] or -galactosyl IgG(PNA)] residues of the Fc domain, respectively. The three IgG preparations exhibited similar hemagglutinating antibody titers (1/100). All experiments were conducted using a coating range of 5000 to 6000 IgG antibody molecules per SRBC. In PM women with E, the rosetting capacity of autologous MCs (percentage of MCs rosetting at least three IgG-SRBCs), their phagocytosing capacity (percentage of MCs ingesting at least three IgG-SRBCs), and the phagocytosis index (number of SRBCs ingested/100 MCs) were similar for each IgG-SRBC preparation considered. In contrast, in PM women without E, the capacity of MCs to phagocytose IgG(PNA)-SRBCs, as well as the phagocytosis index measured with those SRBCs, was strongly reduced (P<0.01 at least), when compared to the same parameters determined using IgG(total)-SRBCs and IgG(Con A)-SRBCs. In addition, when both groups of women were compared, all three Fc-dependent functions measuredin vitro using IgG(PNA)-SRBCs were significantly lower (P<0.01 at least) in women without E than in women on therapy. In another series of experiments, we also found that the rosetting and phagocytosing capacities of MCs were dramatically and transiently reduced in three of three young women during the menstrual period, only when the IgG(PNA)-SRBCs were used as targets. Taken together, our data show that MC phagocytosis of SRBCs coated with IgG antibody exhibiting terminal, and/or accessible, -galactosyl residues in their Fc domain is selectively impaired by a physiological E deficiency and is restored when this deficiency is artificially or spontaneously corrected. They therefore suggest that these hormones are capable of affecting the PNA-like activity of IgG(Fc) receptors of human MCs.