LOCAL HORMONE NETWORKS AND INTESTINAL T-CELL HOMEOSTASIS

Neuroendocrine hormones of the hypothalamus-pituitary-thyroid axis can exert positive or negative immunoregulatory effects on intestinal lym phocytes, Small intestine epithelial cells were found to express recep tors for thyrotropin-releasing hormone (TRH) and to be a primary sourc e of intestine-derived thyroid-stimulating hormone (TSH). The gene for the TSH receptor (TSH-R) was expressed in intestinal T cells but not in epithelial cells, which suggested a hormone-mediated link between l ymphoid and nonhematopoietic components of the intestine, Because mice with congenitally mutant TSH-R (hyt/hyt mice) have a selectively impa ired intestinal T cell repertoire, TSH may be a key immunoregulatory m ediator in the intestine.