Epithelial cell involvement in the estradiol-stimulated accumulation of IgA in the rat uterus.

Immunoglobulin A (IgA) and G (IgG) were analyzed in rat plasma, uterus and uterine secretions by radioimmunoassay and in tissues by immunofluorescent microscopy to determine the mechanism by which estradiol controls IgA and IgG movement from the uterus into the uterine lumen. To determine whether there was evidence for immunoglobulin transport, plasma, tissue and uterine fluid concentrations of IgA and IgG were measured in ovariectomized rats at a time when uterine fluid IgA and IgG were elevated by treatment with estradiol. The concentration of IgA in uterine fluid was 22 times greater than that in tissue indicating that, in response to estradiol, IgA accumulated in the lumen against an apparent concentration gradient. In contrast to IgA, the concentration of IgG in uterine fluid was significantly lower than that in the uterus and in plasma. Immunofluorescent analyses indicated that estradiol has a marked effect on IgA associated with uterine epithelial cells. In saline-injected controls, small amounts of IgA were found in the epithelial cells and in the basement region of these cells. In response to estradiol, IgA accumulated in these cells at a time that coincided with the known increase of IgA in the uterine lumen. No IgA increase was observed when progesterone was given along with estradiol. Similar analyses for IgG, failed to demonstrate epithelial cell involvement of IgG into the uterine lumen. These experiments indicate that in response to estradiol, IgA is moved into the uterine lumen by a mechanism that is distinctly different from that which controls IgG. Since IgA movement is against an apparent concentration gradient, it suggests that estradiol acts on epithelial cells to regulate IgA transport from the uterus into the uterine lumen.