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KATHRYN A. GIBSON, RAKESH K. KUMAR, NICODEMUS TEDLA, IAN GOTIS-GRAHAM, and H. PATRICK McNEIL

ABSTRACT.

Objective. Rheumatoid synovitis is characterized by a mast cell response in which tryptase containing mast cells (MC_T) associate with T lymphocyte infiltration, and tryptase and chymase containing mast cells (MC_TC) correlate more closely with tissue damage or repair events. We investigated expression of the aEb7 integrin and its ligand E-cadherin in rheumatoid and normal synovium and compared this expression to synovial mast cell responses.

Methods. Immunohistochemical analysis was used to determine the expression of aEb7 and E-cadherin in rheumatoid (n = 17) and normal (n = 6) synovium. The density of MC_T and MC_TC mast cell subsets was compared to the density of aEb7 positive mast cells.

Results. The mean density of aEb7 positive cells in rheumatoid synovia was 25.2 cells/mm² (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 mast cells expressed aEb7 compared to 0% in normal synovium (p < 0.0001). There was a strong correlation between the density of aEb7 positive cells and the total mast cell density in rheumatoid synovium (r² = 0.74). aEb7 positive mast cell density correlated significantly with the MC_T subset density (r² = 0.5, p = 0.014), but not with the MC_TC subset density.
E-cadherin expression was increased in rheumatoid compared with normal synovium, but did not colocalize or correlate with aEb7 expression.

Conclusion. These results indicate a role for aEb7 in the mast cell response that occurs in rheumatoid synovitis, in particular the MC_T mast cell subset expansion associated with inflammatory events and interactions with infiltrating lymphocytes. (J Rheumatol 2000;27:2754-60)

Key Indexing Terms:

RHEUMATOID ARTHRITIS
MAST CELLS
aEb7