Immunohistochemical study showed selective localisation of human epidermal growth factor (hEGF) to the synovial lining layer. Although the synovial lining layer of the rheumatoid, osteoarthritic, and traumatic joints was hEGF positive, hEGF staining was especially dense at the rheumatoid synovial lining layer; the staining increasing linearly according to the degree of stratification of the lining layer (r = 1). Human epidermal growth factor was ultrastructurally localised to cytoplasm, especially to rough endoplasmic reticulum, of the synovial lining fibroblast-like (type B) cell. Only the cell surface of macrophage-like (type A) cells was hEGF positive. When different histological variables were compared with each other a positive correlation was found between hEGF staining of the synovial lining layer and the degree of neovascularisation of rheumatoid synovium (r = 0.72). Although some lymphocytes were weakly hEGF positive, neovascularisation did not correlate with the extent of lymphocyte infiltration or of hEGF staining of lymphocytes. Lymphocyte infiltration or hEGF staining of lymphocytes did not correlate with hEGF staining of the synovial lining layer, whereas the lymphocyte infiltration correlated positively with the extent of perivascular accumulation of lymphocytes (r = 0.89). These findings suggest that (a) hEGF is synthesised by and secreted through endoplasmic reticulum and Golgi apparatus from the synovial lining type B cell; (b) hEGF is at least partially responsible for the pathogenesis of stratification of the rheumatoid synovial lining layer, and perhaps of neovascularisation of the rheumatoid synovium, whereas it is not responsible for lymphocyte accumulation to the rheumatoid synovium.
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