Expression and localization of IL-18 in the hypothalamic–pituitary–ovarian axis of non-pregnant, pregnant, and abortive rats

Abstract

Cytokines present in the reproductive system play an important role both in the modulation of immune responses to infectious challenge and in the establishment and maintenance of pregnancy. Interleukin 18 (IL-18) has been regarded as an important regulator of innate and acquired immune response, but its expression and distribution in the hypothalamic-pituitary-ovarian axis remain unclear. In this paper, the expression and distribution of IL-18 in non-pregnant, pregnant, and early abortive rats were examined using an ultra-sensitive immunohistochemical streptavidin-peroxidase method, enzyme-linked immunosorbent assay, and reverse transcription-polymerase chain reaction. The results showed that IL-18 expression in the pituitary, in follicular ovaries, and in the corpus luteum of abortive rats were significantly lower than that of pregnant and non-pregnant rats. However, the staining of IL-18 in the hypothalamus, interstitial glands of the ovary, and uterus of abortive rats was strikingly stronger than those of the non-pregnant ones. IL-18 mRNA expression in rat uterus was detected in all groups, whereas IL-18 mRNA content in abortive rat uterus was significantly higher than in normal pregnant rats. Further, IL-18 in the peripheral blood serum of abortive rats was significantly lower than in same-period normal pregnant rats. The differential expression of IL-18 in early abortion suggests that IL-18 may be related to the underlying mechanisms of abortion.