DENDRITIC CELLS IN SYNOVIAL-FLUID OF CHRONIC INFLAMMATORY ARTHRITIS LACK CD80 SURFACE EXPRESSION

Dendritic cells (DC) act as potent primary antigen-presenting cells in many immune responses and therefore may have a role in the initiation and perpetuation of the synovial inflammation in chronic inflammatory arthritis. To examine their function, it is important to isolate fres h DC from arthritic joints without aberrant activation. We have develo ped a technique using minimal cell manipulation to isolate DC from the synovial fluid of chronic arthritic patients. Using this method, DC w ere shown to be potent allostimulatory cells, with 63-90% of cells lac king lineage-specific markers (lin(-)), but positive for MHC class II molecules. Two morphologically distinct populations of these cells wer e identified in 10 out of 13 DC preparations. Both populations express ed CD40, intercellular adhesion molecule-1 (ICAM-1), ICAM-2, ICAM-3 an d leucocyte function associated antigen-3 (LFA-3), but the predominant population, which was larger and more typical of cultured blood DC, h ad a higher density of these antigens compared with the minor populati on, which were smaller and morphologically similar to lymphocytes. Two new MoAbs which label activated human blood DC, HB15 (CD83) and CMRF- 44, were tested. CD83 labelled very weakly or not at all, whereas CMRF -44 was positive on the larger cells only. Likewise, the costimulator molecule, B7/BB1 (CD80), was not detected on the surface of either syn ovial lin(-) cell population, reverse transcriptase polymerase chain r eaction (RT-PCR) showed little or no CD80 mRNA, and no binding of the CTLA-4Ig fusion protein was found. These results suggest that synovial DC are not, despite the inflammatory environment, in a fully activate d state.