Cumulus oophorus T cells: a possible source of follicular fluid G-CSF, biomarker predictive for embryo implantation in IVF/ICSI cycles

Granulocyte-colony stimulating factor (G-CSF) in individual follicular fluid (FF) may provide a non-invasive biomarker of implantation to be evaluated, to select the oocyte and hence the embryo with the highest implantation potential to transfer in IVF/ICSI cycles. We wonder what could be the source of FF-G-CSF. Since cytokines preferentially act locally, the source of FF G-CSF could be located nearest the oocyte. Cumulus oophorus surrounds the oocyte and then in physiological pregnancy surrounds, breaking up progressively, the derived embryo during the first 72 hours until its implantation. Thus, cumulus could have a strong influence particularly on oocyte and then on embryo development and quality. We found that cumulus T cells produce G-CSF, which could be a) the source of FF G-CSF induced by IL-4 produced by T cells in response to cumulus–derived progesterone and b) responsible together with cumulus derived-progesterone for the cumulus T cells IL-4 production, which in turn could induce the production of LIF by these T cells. Cumulus T cell–derived LIF, which increases the quality of embryos, may provide a microenvironment suitable for embryo pre-implantation development and may explain the increased implantation rate of the embryos associated with high levels FF G-CSF.