CCL4 and polycystic ovary syndrome: In previous observational studies, upregulation of CCR5 expression was observed in the peripheral blood mononuclear cells of patients.[32] Additionally, letrozole-induced PCOS mouse models showed upregulation of CCR5 expression.[33] Furthermore, serum levels of MIP-1α and MIP-1β were higher in PCOS patients than those in the control group.[7]