That mast cells participate in inflammatory reactions is beyond argument. A
major question posed by mast cell biologists is whether specific functions
in inflammation are subserved by different subsets of the mast cell popula
tion. We have investigated the two major subsets of human mast cells (MCT a
nd MCTC), in the chronic inflammatory processes associated with rheumatoid
arthritis (RA). Whereas normal synovium contains mainly MCTC mast cells, th
e MCT subset is selectively expanded in early RA, in numbers that correlate
with synoviocyte hyperplasia and T-lymphocyte infiltration. In contrast, i
n RA of long duration, MCTC mast cells predominate in numbers that correlat
e with clinical indices of rapidity of disease progression. We suggest that
MCT mast cells participate in active inflammatory events, whereas MCTC mas
t cells may be more relevant in repair or damage to connective tissues.