Progesterone-induced-blocking factor 1 (PIBF1) is an immunomodulatory molecule secreted by pregnancy lymphocytes []. It exerts immunosuppressive effects by inhibiting NK cell activity, polarising immune responses towards TH2 dominance and down-regulating effector cytokine response []. It is thought to play a vital role in preventing rejection of the embryo by the maternal immune response. PIBF1 may also have a role in cancer. It is produced by malignant tumours and may facilitate tumour growth by suppressing local antitumour immune responses [].
