The synovial membrane of healthy individuals--immunohistochemical overlap with synovitis.

The synovial membrane of healthy volunteers was analysed by immunohistochemical staining of biopsies sampled under direct vision at arthroscopy or obtained blindly by needle. Infiltrating Leu-4+ T lymphocytes were found scattered in all biopsies but frequently also perivascularly accumulated. A majority of the synovial lining cells expressed either the OKM1 monocyte/macrophage marker or HLA-DR antigens. Some OKM1- HLA-DR+ lining cells also expressed the Leu-3a T 'helper' cell marker. In the sublining tissue non-lymphoid cells with varying morphology including macrophage- and fibrocyte-like cells were found expressing either HLA-DR, or Leu-3a, or both antigens simultaneously, whereas OKM1+ macrophage-like sublining cells were rare. The perivascular T lymphocyte accumulation as well as the phenotypic heterogeneity of infiltrating and residing cells, previously thought indicative of synovitis, were thus also found in the synovial membrane of healthy individuals.