Evaluation of the murine metrial gland for immunological function

The metrial gland (MG) is a transient uterine structure associated with rodent pregnancy. The gland is a complex structure consisting of stromal and vascular elements, as well as a population of histologically distinctive, large, granulated metrial gland (GMG) cells. The functions of the MG and of the GMG cells, as well as their relationship to the success of pregnancy, are unknown. Based upon morphological and morphometric studies it has been proposed that the MG might be involved in the immunology of pregnancy and that GMG cells could be immunocompetent. Explant cultures of MG have therefore been evaluated for immunological function. Lytic activity against the NK sensitive target cell line YAC and mitogen responsiveness could not be detected. MG tissue and medium conditioned by overnight culture of MG tissue (MG-CM) suppressed the response of murine spleen cells to Con A. MG-CM also reduced the lytic activity of splenic NK cells against YAC target cells. However, uptake of [3H]thymidine was elevated when YAC cells were cultured in MG-CM. The response of embryonic and uterine cells to growth in MG-CM was complex. MG-CM had little effect on isotope incorporation by decidual cells recovered at 6.5 days or by embryonic cells recovered from 12.5 day embryos. However, thymidine incorporation was less in MG-CM than in control medium for 12.5 day placental cells, 6.5 day embryonic sac, 6.5 day ectoplacental cone and 3.5 day blastocysts. Cytotoxicity and cytostasis accounted for reduced uptake of isotope in cultures of 3.5 day blastocysts and 6.5 day embryonic tissues. Loss of viability could not be detected in any other assays. Both YAC cells and unstimulated splenocytes showed altered morphology and improved viability when cultured in MG-CM. This study suggests that the only immunological role the MG might have during normal pregnancy is that of non-specific intra-uterine suppression. Alternatively, differential regulation of cell proliferation might be a function of the MG, within the pregnant uterus. The latter mechanism could also account for the apparent observation of non-specific immunosuppression.