IL6 and Infertility: IL-6 is one of the essential cytokines in embryo implantation, and women with unexplained infertility and/or endometriosis present increased levels of secreted IL-6 in the endometrium and other reproductive sites, indicative of an unfunctional endometrium, as this increased IL-6 is also observed in women carrying intrauterine devices (Ammala et al., 1995; Tseng et al., 1996).