T lymphocytes downregulate granulocyte-macrophage colony-stimulating factor secretion from stimulated monocytes by increasing the secretion of monocyte-derived interleukin-10

In previous studies we characterized the cytokine regulation of granulocyte -macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimu lating factor (G-CSF) secretion by endothelial cells and monocytes and foun d differences in secretion pattern within and between these cell systems. I n this study, the regulatory effect of T lymphocytes on CSF secretion was e xamined. T lymphocytes had no effect on CSF secretion by endothelial cells, In contrast, the addition of T lymphocytes significantly and dose dependen tly downregulated GM-CSF, but not G-CSF, secretion by monocytes, In one of our previous studies it was shown that interleukin-1 (IL-4) and interleukin -10 (IL-10) were the most potent inhibitory cytokines of CSF secretion by m onocytes, Both these cytokines are produced by T lymphocytes, However, the downregulating effect on monocyte GM-CSF secretion was not due to increased secretion of T-lymphocyte-derived IL-4 or IL-10, Instead, the presence of T lymphocytes increased the secretion of monocyte-derived IL-10, It was sho wn earlier that IL-10 regulates CSF secretion by monocytes in an autocrine manner. Our data indicate that T lymphocytes might interfere with this auto crine regulation and thereby influence monocyte function in immune response and cell proliferation, (C) 1999 International Society for Experimental He matology, Published by Elsevier Science Inc.