Synovial fluids from patients with rheumatoid arthritis induce the differentiation of human promyelocytic leukemia cell line HL 60]

Bone marrow abnormalities have been found to play a role in the pathogenesis of rheumatoid arthritis (RA). Recent studies have also confirmed the presence of undifferentiated hematopoietic progenitor cells as well as the expression of stem cell factor in the synovial membranes in RA. The present study investigates whether RA synovial fluids contain factors that can induce differentiation of CD 14 positive/HLA-DR positive cells from undifferentiated hematopoietic cells. Synovial fluid specimens from 18 patients with RA and from 10 control patients, including patients with osteoarthritis and Behcet's disease, were studied. Human promyelocytic leukemia cell line HL 60 (5 x 10(4)/well) were cultured in the presence or absence of the synovial fluids for 5 days, after which the expression of CD 14 and HLA-DR was examined by flow cytometry. The induction of differentiation of CD 14 positive/HLA-DR positive cells or HLA-DR positive cells from HL 60 cells was significantly enhanced more in the presence of synovial fluids from RA patients than in the presence of those of control patients. However, the sera from the RA patients could not induce the differentiation of CD 14 positive/HLA-DR positive cells or HLA-DR positive cells from HL 60 cells. Most cytokines found in RA synovial fluid could not induce the differentiation of HL 60 cells. Of note, treatment of synovial fluids with hyaluronidase significantly decreased or abrogated their capacity to induce the differentiation of HLA-DR positive cells from HL 60. There was no significant difference in the concentration of hyaluronic acid in the synovial fluid between the RA patients and the control patients. These results indicate that there are factors that can induce differentiation of HLA-DR positive cells from undifferentiated hematopoietic cells in the synovial fluid of RA. The data also suggest that such differentiation factors might be related with qualitative abnormality of hyaluronic acid.