Expression of HLA-DR and HLA-DQ antigens on cells within the cartilage-pannus junction in rheumatoid arthritis.

The cartilage-pannus junction in joints from patients with active rheumatoid arthritis was studied by means of immunohistochemical analysis of frozen sections, using monoclonal antibodies directed against HLA-DR, HLA-DQ class II transplantation antigens, against the transferrin receptor and against T-lymphocyte subpopulations. Expression of HLA-DR antigens was seen on a large number of synovial cells in immediate contact with the cartilage, whereas the expression of HLA-DQ antigens was only seen on a subfraction of the HLA-DR-positive cells. Most of the cells in close contact with the cartilage expressed the transferrin receptor, indicating a proliferative state of these cells. It is suggested that class II antigen-expressing synovial cells in immediate contact with the cartilage in rheumatoid joints might, in addition to their potential role in the destructive process, also serve functions in the elicitation of immune reactions against molecules released from the cartilage.