TNF-RECEPTORS ON HUMAN PERITONEAL MESOTHELIAL CELLS - REGULATION OF RECEPTOR LEVELS AND SHEDDING BY IL-1-ALPHA AND TNF-ALPHA

Human peritoneal mesothelial cells (HPMC) respond to tumor necrosis fa ctor alpha (TNF alpha) by releasing various cytokines that may activat e the endothelium and induce recruitment of leukocytes during peritoni tis. We characterized the receptors for TNF on HPMC to elucidate their functions in peritonitis. Scatchard analysis determined the presence of 70 x 10(3) TNF receptors/cell with a kDa of 0.44 nM. TNF receptor 1 (TNF-R1, p55) and TNF-R2 (p75) mRNA were demonstrated by reverse-tran scriptase-PCR (RT PCR). TNF-R1 protein was solely detected by flow cyt ometry (FCM). Interleukin-1 alpha (IL-1 alpha) induced down-regulation of TNF-R1. This was concomitant with accumulation of soluble TNF-R1 ( sTNF-R1) detected by specific ELISA. LPS had a lower TNF-R1-shedding a ctivity while TNF alpha did not induce shedding. The IL-1-induced-s TN F-R1-shedding was suppressed by the protein-kinase-A (PKA) inhibitor, H-8, or by H-7, the inhibitor of both PKC and PKA, but not by the spec ific PKC inhibitor GF. These experiments suggest a role for PKA in the IL-1-shedding signal. No change in TNF-R1 mRNA levels was observed af ter IL-1 alpha or TNF alpha stimulation while TNF-R2 (p75) mRNA basal levels transiently increased three to fivefold, reaching a peak after four hours followed by an accumulation of sTNF-R2 in the supernatant. Our data suggest that the main receptor expressed on HPMC is TNF-R1. D own-regulation and shedding of TNF-R1 induced by IL-1, and the transie nt expression of TNF-R2 induced by IL-1 and TNF, may regulate the resp onses to TNF by HPMC. These results may be important in understanding the inflammatory process of peritonitis were TNF plays a major role.