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Corticotropin-releasing factor mRNA in rat thymus and spleen
F Aird1, C V Clevenger, M B Prystowsky
1Department of Psychiatry, University of Pennsylvania, Philadelphia 19104.
Insights
Corticotropin-releasing factor (CRF) is synthesized in the rat spleen and thymus, not just the brain. This locally produced "immune" CRF may directly regulate immune cell function.
Area of Science:
- Immunology
- Neuroendocrinology
- Molecular Biology
Background:
- Corticotropin-releasing factor (CRF) plays a role in stress-induced immunosuppression via the hypothalamic-pituitary-adrenal axis.
- CRF also exhibits direct effects on immune cells, with previous studies detecting it in the rat spleen and thymus.
Purpose of the Study:
- To investigate whether CRF is synthesized within the spleen and thymus.
- To explore the local synthesis and secretion of CRF in immune tissues.
Main Methods:
- Analysis of CRF mRNA in rat spleen and thymus using reverse transcription and polymerase chain reaction (PCR).
- Southern blotting and hybridization with a CRF gene probe.
- Culturing of splenic and thymic adherent cells to assess CRF secretion.
Main Results:
- CRF mRNA was detected in spleen, thymus, and hypothalamus, but not in liver or kidney.
- CRF was secreted from cultured splenic and thymic adherent cells.
- Secretion was enhanced by nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, but unaffected by interleukin-1.
Conclusions:
- The spleen and thymus synthesize CRF, indicating local production of this factor within immune tissues.
- Locally synthesized CRF may act as an autocrine or paracrine cytokine, directly influencing immune function.
- Regulation of CRF secretion in immune tissues may differ from that in the hypothalamus.
Abstract:
Corticotropin-releasing factor (CRF) initiates stress-induced immunosuppression via the hypothalamic-pituitary-adrenal axis. CRF has also been 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 these tissues, we analyzed rat spleen and thymus for the presence of CRF mRNA. RNA was reverse transcribed, and the resulting cDNA was amplified by the polymerase chain reaction with CRF gene-specific oligonucleotide primers. After Southern blotting and hybridization with an internal CRF gene probe, a product of the expected size was detected in the spleen, 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 inhibitor, whereas interleukin 1 had no effect, suggesting that regulation of CRF secretion may differ from that in the hypothalamus. CRF mRNA was detected in NDGA-stimulated thymic adherent cells and in both control and NDGA-stimulated splenic nonadherent cells. The finding that CRF is synthesized in the spleen and thymus suggests that locally synthesized "immune" CRF, acting as an autocrine or paracrine cytokine, may have direct regulatory effects on immune function.