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
determined in vitro by a classical rosette assay in 12 postmenopausal (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, alpha-mannosyl [IgG(Con A)] or beta-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 less than 0.01 at least), when compared to the same
parameters determined using IgG(total)-SRBCs and IgG(Con A)-SRBCs.