Expression of allograft inflammatory factor-1 in peripheral blood monocytes and synovial membranes in patients with rheumatoid arthritis

ObjectiveAllograft inflammatory factor-1 (AIF-1) is a cytoplasmic protein expressed in various human cells such as monocyte/macrophages and activated T lymphocytes. A recent study showed that AIF-1 is strongly expressed in infiltrating mononuclear cells and synovial fibroblasts in rheumatoid arthritis and that AIF-1 induces the proliferation of cultured synovial cells. In this study we analysed the expression of AIF-1 in peripheral blood monocytes and synovial membranes from patients with rheumatoid arthritis (RA).MethodsWe examined 71 patients with rheumatoid arthritis and 25 control subjects.ResultsUsing flow cytometry we found significantly increased numbers of circulating AIF-1+ monocytes in peripheral blood from RA patients compared with controls. Moreover, there were statistically significant positive correlations between AIF-1+ monocytes, DAS28 and the Sharp erosion score.Immunofluorescence staining showed strong expression of AIF-1 by infiltrating mononuclear cells – predominantly macrophages in RA synovial tissues – compared with tissues derived from joints affected by osteoarthritis.ConclusionThe results of this study suggest that AIF-1 may be associated with the pathogenesis of RA and may be a novel cytokine involved in the immunological process underlying RA.