The uterus itself is capable of interacting with the ovary via luteolytic substances, mainly prostaglandins produced by the endometrial glands. The non-gravid uterus is relatively resistant to infection while under the influence of estrogen. The cervix provides an efficient protective barrier for the uterus. The normal cervix is closed during the luteal phase of the cycle and is patent during estrus. Local antibody production and phagocytosis via opsonins are important defense mechanisms in limiting the duration of uterine infections.
Cytokines play important roles as autocrine and paracrine regulators.
In ruminants, the best described such example is the role of interferon-gamma in the reproductive tract. The normal endometrium is capable of mounting a local response to invading pathogens, thereby maintaining a sterile environment. To initiate immune response, it is necessary to have cells present for antigen recognition and presentation to immunoregulatory lymphocytes and macrophages. Endometrial lymphocytes are intraepithelial lymphocytes with functional characteristics similar to those in the gut. Females treated with progesterones are more likely to develop infections after intrauterine installation of bacteria.