Type I interferon required for maintaining basal levels of IFN-regulated genes, including 2'-5'-oligoadenylate synthetase, IRF7 and ISG15, in the female reproductive tract. Directly mediates protection against viral and bacterial genital infections (By similarity). Endometrium-specific. Highly expressed in endometrial epithelial cells in proliferative phase of the menstrual cycle. Levels decrease approximately 10-fold in the secretory phase. Virtually undetectable in samples from postmenopausal women. By estrogens. Belongs to the alpha/beta interferon family.