MONOSODIUM URATE, HYDROXYAPATITE, AND CALCIUM PYROPHOSPHATE CRYSTALS INDUCE TUMOR-NECROSIS-FACTOR-ALPHA EXPRESSION IN A MONONUCLEAR CELL-LINE

Objective. Tumor necrosis factor-alpha (TNF-alpha) is thought to be im portant in chronic inflammation of joints characteristic of crystal in duced arthritis. Monocytes are instrumental in maintaining that inflam mation. We investigated production of mRNA and protein for TNF-alpha i n vitro in a murine mononuclear cell line, after exposure to relevant crystal types. Methods. Using the cell Line designated RAW 264.7, cell s were grown in standard medium and exposed to varying amounts of mono sodium urate (MSU), hydroxyapatite (HA), and calcium pyrophosphate dih ydrate (CPPD) crystals for differing time periods. Analysis of TNF-alp ha mRNA induced by such exposure was by Northern hybridization; analys is of TNF-alpha protein was by ELISA. Results. RNA analyses of cells t reated with various levels of MSU, HA, and CPPD crystals showed strong induction of TNF-alpha transcripts. ELISA on culture supernatants con firmed high level TNF-alpha. peptide secretion resulting from that tra nscriptional upregulation. Time course studies showed peak accumulatio n of TNF-alpha mRNA 1-6 h post-treatment. Study of the signalling path way involved in TNF-alpha transcriptional upregulation indicated that increased phospholipase A(2) activity was required. Conclusion. These observations suggest that crystals in joints can directly stimulate pr oduction of TNF-alpha, and that the source of that cytokine may be the monocytes known to be present and playing an important role in chroni c joint disease.