Mast cells and fibroblast-like synoviocytes co-culture increases interleukin-6 secretion in rheumatoid arthritis

Abstract

To explore the significance of mast cells-fibroblast like synoviocytes (FLS) interaction in the pathogenesis of rheumatoid arthritis (RA). Frozen sections of RA synovia from 4 patients were made to observe the distribution of mast cells by immunochemistry. FLSs were isolated from 4 samples of RA synovia and co-cultured with the human mast cells of the line LAD-2 for 0, 12, 24, and 48 h, and 7 d. ELISA was used to detect the interleukin (IL)-6, an important proinflammatory cytokine. 4% formaldehyde was used to fix the FLS and LAD-2 cells and then detect the IL-6 levels in the supernatant. Other FLS and LAD-2 mast cells were put into the upper and lower chambers of Transwell system to be cocultured in isolate condition, an important proinflammatory cytokine. Microscopy showed that FLSs were adjacent to the mast cells. The IL-6 content of the FLS/LAD-2 cell co-culture supernatant was 7150 microg/L +/- 114 microg/L, significantly higher than that of the FLS supernatant (3019 microg/L +/- 57 microg/L, P < 0.01). LAD-2 cell number dose-dependently increased the IL-6 content in the supernatant. Almost no IL-6 secretion was found in the supernatant of the co-culture with fixed FLSs and non-fixe4d LAD-2 cells, and the IL-6 secretion in the supernatant of the co-culture with fixed LAD-2 cells and non-fixed FLSs was similar to that of the single FLS group and far lower than that of the FLS-LAD-2 co-culture group. Transwell system test showed that there was no significant difference in the IL-5 level between the direct mixture co-culture group and indirect mixture co-culture. Mast cell/FLS interaction increases the IL-6 secretion via soluble mediators, thus playing an important role in the pathogenesis of RA.