CORTICOTROPIN-RELEASING FACTOR MESSENGER-RNA IN RAT THYMUS AND SPLEEN

Corticotropin-releasing factor (CRF) initiates stress-induced immunosu ppression via the hypothalamic-pituitary-adrenal axis. CRF has also be en shown to have direct stimulatory and suppressive effects on immune cells. We have previously detected immunoreactive and bioactive CRF in the rat spleen and thymus. To determine if CRF is synthesized in thes e tissues, we analyzed rat spleen and thymus for the presence of CRF m RNA. RNA was reverse transcribed, and the resulting cDNA was amplified by the polymerase chain reaction with CRF gene-specific oligonucleoti de primers. After Southern blotting and hybridization with an internal CRF gene probe, a product of the expected size was detected in the sp leen, thymus, and hypothalamus (positive control) but not in liver or kidney (negative controls), indicating that CRF is synthesized in the spleen and thymus. Furthermore, CRF could be secreted from splenic and thymic adherent cells in culture. Secretion increased severalfold in response to nordihydroguaiaretic acid (NDGA), a lipoxygenase pathway i nhibitor, whereas interleukin 1 had no effect, suggesting that regulat ion of CRF secretion may differ from that in the hypothalamus. CRF mRN A was detected in NDGA-stimulated thymic adherent cells and in both co ntrol and NDGA-stimulated splenic nonadherent cells. The finding that CRF is synthesized in the spleen and thymus suggests that locally synt hesized ''immune'' CRF, acting as an autocrine or paracrine cytokine, may have direct regulatory effects on immune function.