Lack of CD80 expression by fibroblast‐like synoviocytes leading to anergy in T lymphocytes

Objective To investigate whether contact with HLA–DR+, but CD80−, fibroblast‐like synoviocytes (FLS) in the presence of antigen leads to the induction of anergy in, rather than stimulation of, T cells. Methods Cell surface expression of activation and costimulatory markers on FLS were studied by flow cytometry. Functional changes were investigated by T cell proliferation to tuberculin purified protein derivative or allogeneic responses to FLS, in the presence or absence of DAP3.B7 cells, a human CD80‐transfected mouse fibroblast cell line. Induction of anergy was investigated by a 2‐stage culture system. T cells were cocultured with allogeneic FLS in the primary culture, rested, and restimulated in the secondary culture by FLS in the presence or absence of DAP3.B7 cells or interleukin‐2 (IL‐2). Results Direct contact between T cells and FLS caused up‐regulation of CD69 on T cells and HLA–DR on FLS in both the allogeneic and autologous cultures. The addition of DAP3.B7 cells to FLS–T cell cocultures restored the depressed allogeneic responses of T cells. The allogeneic response by T cells to FLS in the presence of DAP3.B7 cells could be completely inhibited by blocking CD80 with CTLA‐4 Ig. Indirect evidence that T cells cocultured with FLS were anergic was the up‐regulation of CD25, negligible T cell proliferation, and the restoration of proliferation by the addition of exogenous IL‐2. Direct evidence of anergy was obtained when T cells from the primary cultures with FLS remained unresponsive to secondary culture with FLS even in the presence of DAP3.B7 cells. In contrast, primary culture of T cells with FLS plus DAP3.B7 cells initiated a good allogeneic response in all subsequent cultures. Conclusion It is possible that T cells within the synovium may be anergized by contact with HLA–DR+ CD80− FLS.