Expression of the alpha E beta 7 integrin by mast cells in rheumatoid synovium

Objective. Rheumatoid synovitis is characterized by a mast cell response in which tryptase containing mast cells (MCT) associate with T lymphocyte inf iltration, and tryptase and chymase containing mast cells (MCTC) correlate more closely with tissue damage or repair events. We investigated expressio n of the alphaE beta7 integrin and its ligand E-cadherin in rheumatoid and normal synovium and compared this expression to synovial mast cell response s, Methods. Immunohistochemical analysis was used to determine the expression of alphaE beta7 and E-cadherin in rheumatoid (n = 17) and normal (n = 6) sy novium. The density of MCT and MCTC mast cell subsets was compared to the d ensity of alphaE beta7 positive mast cells. Results. The mean density of alphaE beta7 positive cells in rheumatoid syno via was 25.2 cells/mm(2) (range 0.3-102.9), of which 26.7% (range 0-68.6%) were mast cells. A mean of 11.9% (range 0-30.4%) of rheumatoid synovial mas t cells expressed alphaE beta7 compared to 0% in normal synovium (p < 0.000 1). There was a strong correlation between the density of <alpha>E beta7 po sitive cells and the total mast cell density in rheumatoid synovium (r(2) = 0.74). alphaE beta7 positive mast cell density correlated significantly wi th the MCT subset density (r(2) = 0.5, p = 0.014), but not with the MCTC su bset density, E-cadherin expression was increased in rheumatoid compared wi th normal synovium, but did not colocalize or correlate with alphaE beta7 e xpression. Conclusion. These results indicate a role for alphaE beta7 in the mast cell response that occurs in rheumatoid synovitis, in particular the MCT mast c ell subset expansion associated with inflammatory events and interactions w ith infiltrating lymphocytes.