Objective: To explore the significance of mast cells-fibroblast like synoviocytes (FLS) interaction in the pathogenesis of rheumatoid arthritis (RA).
Methods: 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.
Results: 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.
Conclusion: Mast cell/FLS interaction increases the IL-6 secretion via soluble mediators, thus playing an important role in the pathogenesis of RA.