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

Abstract

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.