To study the consequences of mast cell activation in human synovial tissue.
Synovial tissue was obtained from 18 RA patients and mast cells was selectively activated in synovial tissue explant cultures. Expression of TNF-alpha, IL-1beta and IL-1Ra were determined and tissue distribution of IL-1beta was studied.
Compared to untreated synovia, selective activation of synovial mast cells increased significantly the production of TNF-alpha (0.49 +/- 0.88 vs. 4.56 +/- 3.18 pg/mg wet tissue, p < 0.001) and IL-1beta (0.058 +/- 0.032 vs. 2.55 +/- 1.98 pg/mg wet tissue, p = 0.013). The expression of TNF-alpha and IL-1beta mRNA increased significantly (19-fold (p = 0.009) and 13-fold (p = 0.031), respectively). Mast cell activation induced IL-1beta expression in particular in nearby CD68 positive synovial macrophages. Secretion of IL-1Ra was also increased but to a lesser degree than that of IL-1beta.
Synovial mast cells produce proinflammmatory cytokines and may thus contribute to the inflammation in RA.