Human cathelicidin antimicrobial protein 18 (hCAP18/LL-37) is increased in foetal membranes and myometrium after spontaneous labour and delivery.

Infection and/or inflammation are most commonly associated with preterm birth. Studies have shown that antimicrobial peptides can modulate the inflammatory response in non-gestational tissues; the human cathelicidin hCAP18 (and its active component LL-37) has such anti-microbial and immunomodulatory properties. The aim of this study was to determine the effect of human labour on hCAP18 expression in foetal membranes and myometrium, and to determine the effect of the synthetic LL-37 peptide on pro-inflammatory and pro-labour mediators in foetal membranes and myometrium. The localisation and expression of hCAP18 in non-labouring and labouring tissues was determined by immunohistochemistry and Western blot, respectively. Tissue explants were used to determine the effect of LL-37 on pro-labour mediators. hCAP18 was localised to the amnion epithelium, cytotrophoblasts and decidua in the foetal membranes, and in the longitudinal and transverse muscle fibres of the myometrium. Additional hCAP18 staining was present in leukocytes. In foetal membranes and myometrium, human labour was associated with significantly higher hCAP18 protein expression. Treatment of foetal membranes and myometrium with LL-37 significantly induced the expression and secretion of the pro-inflammatory cytokines IL-6 and TNF-α, and the chemokines IL-8 and MCP-1. LL-37 also induced expression of MMP-9 mRNA and pro MMP-9 expression in foetal membranes. Co-treatment with BAY 11-7082 was associated with a decrease in LL-37-induced pro-inflammatory cytokine expression. Moreover, inhibition of MyD88 in myometrial cells decreased LL-37-induced pro-inflammatory cytokine expression and release. LL-37 also significantly increased NF-κB transcriptional activity. In conclusion, hCAP18/LL-37 induces pro-inflammatory and pro-labour mediators, via the MyD88/NF-κB pathway.