InterPro domain: IPR026205

Progesterone-induced-blocking factor 1 (PIBF1) is an immunomodulatory molecule secreted by pregnancy lymphocytes [ 1 ]. It exerts immunosuppressive effects by inhibiting NK cell activity, polarising immune responses towards TH2 dominance and down-regulating effector cytokine response [ 2 ]. 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 [ 3 ].

1. The mechanism of the inhibitory effect of progesterone on lymphocyte cytotoxicity: I. Progesterone-treated lymphocytes release a substance inhibiting cytotoxicity and prostaglandin synthesis. Am J Reprod Immunol Microbiol 9, 15-8
2. PIBF (progesterone induced blocking factor) is overexpressed in highly proliferating cells and associated with the centrosome. Int. J. Cancer 112, 51-60
3. PIBF: the double edged sword. Pregnancy and tumor. Am. J. Reprod. Immunol. 64, 77-86