Corticotrophin-releasing factor (CRF) from the hypothalamus stimulates corticotrophin (ACTH) secretion. Concentrations of CRF in the peripheral circulation are normally low, and increase during pregnancy due to CRF secretion by the placenta [Cunnah, Jessop, Besser & Rees (1987) J. Endocrinol. 113, 123-131], although CRF in maternal blood does not appear to stimulate the hypothalamo-pituitary-adrenal (HPA) axis [Potter, Behan, Fischer, Linton, Lowry & Vale (1991) Nature (London) 349, 423-426]. We have examined the possibility that the placental. CRF might contribute to the suppression of the maternal immune system, which is necessary to prevent rejection of the foetus, by studying endotoxin-evoked cytokine production by monocytes as a model for activation of the immune response. CRF inhibited endotoxin-evoked cytokine production from human mononuclear cells (MNCs), the fraction of peripheral blood containing monocytes. The effects of CRF were reversed by a specific CRF receptor antagonist, and were additive with glucocorticoid inhibition of cytokine secretion. Anti-interleukin-1 (IL-1) antisera inhibited endotoxin-evoked IL-6 production; however, the CRF effect was not additive, suggesting that CRF inhibition of IL-6 production may be secondary to CRF inhibition of IL-1. These results suggest a role for CRF as an immunosuppressant during pregnancy.

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