Estradiol induced alterations of the immune system--I. Enhancement of IgM production

Estrogens have been postulated as natural modulators of the immune system. In this study we have evaluated the effect of estradiol on in vivo immunoglobulin production in male rats. Administration of either a 75 microgram/kg or 750 microgram/kg dose of estradiol resulted in a dose-related increase of anti-sheep red blood cell antibody titers during a primary antibody response. These same animals when dosed with estradiol during a secondary antibody response showed an earlier appearance of the peak antibody titer in estradiol-treated rats as compared to controls. Rats dosed with estradiol only during the secondary antibody response period also showed a dose-related increase in Ab titer over control values but no shift in the time of appearance of the peak titer. Treatment of sera with 2-mercaptoethanol to evaluate IgG titers showed that 2-mercaptoethanol treatment both reduced the titer to control values and eliminated the estradiol-induced shift in the appearance of the peak antibody titer in rats given estradiol during the primary and secondary antibody response periods. Sera from animals dosed with estradiol during the secondary antibody response period only also showed titers reduced to control levels after 2-mercaptoethanol treatment of the sera. Estradiol-treated rats also had an increase in antibody titers to polysaccharide from Type III pneumococci, a T-cell independent antigen. While total antibody responses were increased following estradiol, there were no differences in the number of antibody-producing cells between control and estradiol-treated animals. The results of these studies suggest that estradiol exerts a direct effect on B cells resulting in increased synthesis of IgM antibodies. We cannot rule out, however, some modulation through regulatory T-cells.