EXPRESSION OF CD60 ON MULTIPLE CELL LINEAGES IN INFLAMMATORY SYNOVITIS

BACKGROUND: CD60 is a recently described T cell subset marker that is expressed on the surface of most T lymphocytes in synovial tissue and fluid and on a smaller proportion of peripheral T cells. Activation of T lymphocytes can be triggered through CD60. CD60 is also expressed b y neuroectodermally derived cells in thymic epithelium and in skin. EX PERIMENTAL DESIGN: Immunohistologic analysis of CD60 expression in syn ovium and thymus was performed using formalin-fixed tissue samples. No nlymphoid cell lines grown from similar tissues were analyzed by flow cytometry. RESULTS: CD60 was readily identified in formalin-fixed, par affin-embedded tissues. Simultaneous examination of CD60 distribution and cell morphology demonstrated that, in addition to its presence on T cells, CD60 was also expressed by a variety of nonlymphoid cells in synovium, including synovial Lining cells, vascular endothelium, and d endritic-appearing cells deep within synovial tissue. Synovial tissue expression of CD60 was similar in rheumatoid arthritis and in other fo rms of inflammatory arthritis. In addition, it was strongly expressed by giant cells in pigmented villonodular synovitis. Surface expression of CD60 was detected by flow cytometry on cultured synoviocytes and o n other CD60+ nonlymphoid cells, thus excluding adsorption of CD60 she d by T cells as a sufficient explanation of the immunohistologic findi ngs. CONCLUSIONS: These results define the T cell-activating CD60 dete rminant as a broadly distributed Ag within synovial tissue, with a pos sible functional role in the activation of a variety of cellular popul ations. CD60 may also be a marker for previously undescribed cell subs ets in the synovial compartment, possibly including a cell population of neuroectodermal origin.