Transient Expression of CC Chemokine TECK in the Ovary during Ovulation: Its Potential Role in Ovulation

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Abstract
Chemokine thymus-expressed chemokine (TECK), which is expressed exclusively in the thymus and small intestine, plays a critical role in T-cell development. Our previous study revealed its expression in the ovary also. This study investigated its ovarian expression during ovulatory process. Super-ovulation was induced in young female CD1 mice by equine chorionic gonadotropin (eCG) and human chorionic gonadotropic (hCG). Ovarian TECK expression during ovulation was determined by: (1) reverse transcriptase-polymerase chain reaction (RT-PCR) at mRNA level, (2) Western blot and immunohistology at the protein level, and (3) leukocyte infiltration assay at the bioactive level. A transient, high-level expression of TECK in murine ovaries at the mRNA level during hCG-induced ovulation was detected. Sequencing of directly cloned PCR product confirmed the ovarian expression of TECK. The peak expression of TECK was observed at 10-12 hr post-hCG injection; real-time PCR revealed an 800-fold increase during its expression peak over 0 hr. The expressed ovarian TECK protein was readily detectable by Western blot. Immunohistochemistry localized TECK expression to the ovarian interstitial tissue surrounding, or in the theca layer of the mature follicles undergoing ovulatory process. Expression of TECK receptor, the CC chemokine receptor (CCR9) was also detected in the ovulating ovaries. Using in vitro leukocyte infiltration assay, we first demonstrated that ovaries undergoing the ovulatory process were able to selectively chemoattract mononuclear cells. Importantly, neutralization of TECK by the antibody resulted in a 85% reduction in the chemotactic activities of the ovaries. This study suggested that ovarian expression of TECK is under a tight hormonal regulation, and expressed TECK may be responsible for recruitment of mononuclear cells into the ovary to participate in the ovulatory process.