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Antimicrobial peptides (AMPs) are small proteins produced by epithelial surfaces, which have broad-spectrum antimicrobial and immunomodulatory activities. In the lung, skin and alimentary tract AMPs are known to be important in infectious and inflammatory conditions. Far less is known regarding the role of AMPs within the female reproductive tract, but as infection and inflammation are causes of preterm labour, AMPs may have a key function in maintain and protecting pregnancy. The major groups of human AMPs include the human beta defensins (HBDs), two antileukoproteinases (secretory leukocyte protease inhibitor (SLPI) and Trappin-2/Elafin), and the human cathelicidin hCAP18/LL-37, with several studies identifying their presence at sites throughout the reproductive tract. The cervix in pregnancy is positioned between the upper genital tract containing the developing fetus and the lower tract where infections usually arise. I hypothesise that AMPs are fundamental to mucosal immune defence of the cervix in pregnancy, preventing ascending infection and excessive inflammation that can cause preterm labour. This thesis focused on the human cathelicidin hCAP18/LL-37 and its role within the cervix and vagina. The aims of this thesis were to; investigate the inflammatory effects of LL-37 from cervical and vaginal derived epithelial cells and determine the pathways and receptors in which LL-37 may elicit its effects and how production may be regulated; investigate the role of CRAMP in a mouse model of preterm birth; and determine the production of AMPs by the pregnant cervix whilst investigating the relationship between AMP concentrations in cervicovaginal secretions and preterm labour. The inflammatory effect of LL-37 was investigated using cell lines derived from endocervical, ectocervical and vaginal epithelium. The study of these cell lines suggests divergent responses of cervical and vaginal epithelial cells. LL-37 mediated induction of IL-8 and IL-6 production from endocervical epithelial cells was observed in a dose-dependent and time-dependent manner, whilst ectocervical and vaginal cells also respond to treatment with LL-37 through IL-8 and IL-6 production. To determine a possible mechanism of action of LL-37 on IL-8 and IL-6 in the three cell lines, inhibitors against MAPK cascades, ERK, p38 MAPK and JNK, and known LL-37 receptors were investigated. In endocervical cells LL-37 mediated IL-8 occurs via activation of unidentified GPCRs, whilst in ectocervical cells this effect on IL‐8 and IL-6 is via the activation of ERK and p38 MAPK cascades. The mechanism by which LL-37 induces IL-8 secretion in vaginal epithelial cells remains unknown. Expression of LL-37 was shown to be mediated by vitamin D3 in vitro in cervical and vaginal epithelial cells. However when this relationship was investigated in vivo, using matched serum and cervicovaginal secretions from woman at early pregnancy, no correlation was observed between circulating vitamin D and cervicovaginal or circulating hCAP18/LL-37. However, the majority of women in this study reported with insufficient levels of vitamin D, which may effect the relationship observed with hCAP18/LL-37. Using a mouse model of LPS-induced preterm labour, to mimic the presence of intrauterine infection bacterial infection, I aimed to characterise the role of CRAMP, the mouse orthologue of hCAP18/LL-37, in the lower inflammatory and immune response that results in preterm labour. Wild type C57Bl/6J mice receiving an intrauterine injection of LPS deliver prematurely, within 24 hours of injection. However mice deficient in CRAMP (Camp -/-) receiving an intrauterine injection of LPS deliver significantly later and have a non-significant increase in pup survival compared to wild type C57Bl/6J mice. Cervical tissue collected post partum showed no difference in inflammatory markers between wild type C57Bl/6J and Camp -/- mice, however there was increased expression of the neutrophil chemoattractant marker, Cxcl5, and the neutrophil marker, Ngp in Camp -/- mice. In the lower genital tract, levels of antimicrobial peptides were determined in samples of cervicovaginal secretions collected from pregnant women. AMPs, hCAP18/LL-37, HBD-2 and SLPI were found in cervicovaginal secretions, and levels of hCAP18/LL-37 were increased in women with the common vaginal infection bacterial vaginosis. However no relationship was identified between the concentration of AMPs and preterm birth in this study. This work has shown that the lower genital tract, where infections that are associated with preterm labour originate, expresses the human cathelicidin hCAP18/LL-37. It may play an important role in modulating the immune response to invading infection associated with preterm labour. Further investigation of these responses may increase understanding of the physiology and pathophysiology of labour, and lead to strategies for the prevention of premature delivery. |
