Identification of constitutively expressed chemokines in the mouse female reproductive tract

INTRODUCTION: Leukocyte recruitment to the female reproductive tract (FRT) is critical for protection against infection, and for remodelling during the estrus cycle, pregnancy and during post-partum uterine involution. Previous studies have shown that leukocytes, including macrophages, neutrophils and T cells are present within the non-pregnant uterus in mice. The chemokines involved in the recruitment of these cells to the uterus, and the function of these cells remains unclear.
OBJECTIVES: Chemokines are required for driving tissue-specific leukocyte homing, yet little is known about their expression within the FRT in mice, during the normal estrus cycle. The first aim of this study was to characterise the chemokine profile of distinct anatomical compartments of the mouse FRT at each estrus cycle stage. In addition, our second aim was to examine immune cell populations present within the mouse uterus during the various estrus cycle stages.
MATERIALS AND METHODS: Ovary, uterine horn, cervix and vagina were obtained from non-pregnant C57/BL6 mice (n = 20) during proestrus, estrus, metestrus and diestrus. Taqman Low Density Arrays were used to analyse the expression of 34 chemokines and 11 chemokine receptors within these tissues, with lung, skin, small intestine and colon used as control tissues. Several markers of leukocyte populations (F4/80, neutrophil granule protein, CD3, CD11c, CD19, CD49b, MBP) were analysed by qPCR. Differences in expression between tissues, and between estrus cycle stage were assessed by the Kruskal-Wallis test, followed by the Dunn's Multiple Comparison Test.
RESULTS: Of the four uterine tissues examined, the uterine horn exhibited expression of the largest number of chemokines. CCL28 and XCL1 were predominantly expressed within the uterine horn, with CCL28 expression being 20-fold higher than the ovaries (p < 0.05), 50-fold higher than the cervix (p < 0.0001) and 14-fold higher than the vagina (p < 0.05). XCL1 expression was approximately 20-fold higher than the ovaries and cervix, and 30-fold higher than the vagina (all p < 0.0001). Interestingly, CCL27 was the only chemokine found to be highly expressed in the ovaries. Differences in chemokine and chemokine receptor expression between estrus cycle stages were minimal, although CCL7 and CCR4 were of interest. CCL7 expression was lower during estrus and metestrus in the ovary (p < 0.0269), cervix (p < 0.0216) and vagina (p < 0.015), and CCR4 expression was reduced during diestrus in the ovary (p < 0.0212), uterine horn (p < 0.0291) and vagina (p < 0.0051). Analysis of leukocyte marker expression suggests that the uterine horn is the principal home of most leukocyte subsets within the FRT.
CONCLUSIONS: This study was designed to identify chemokines and/or receptors which are highly expressed within tissues of the mouse FRT, and has provided us with targets for future study. Of particular interest in the high expression of CCL27 within the ovary and expression of CCL28 and XCL1 within the uterine horn, and these chemokines will be examined in more depth in future studies.