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, including HSV-2, and bacterial, including Chlamydia muridarum, genital infections. Expressed at very high levels in uterus and, at much lower levels, in ovary and cervix. Very low levels, if any, in other organs. In the endometrium, expressed in the luminal and glandular epithelial cells (at protein level). Expression varies approximately 30-fold during the estrous cycle, with lowest levels during diestrus and highest at estrus. During pregnancy, uterine expression is dramatically reduced at 1.5 dpc and reaches its lowest levels at 4.5 dpc, coincident with the time of embryo implantation. By estrogens. Contrary to other type I interferons, not induced by known pattern-recognition receptor pathways. Mutant females are substantially more susceptible to (and less able to clear) an ascending infection in the reproductive tract than wild-type animals. Belongs to the alpha/beta interferon family.