Spontaneous and anti-Fas antibody-mediated apoptosis of the peripheral blood lymphocytes in Sjögren’s syndrome, rheumatoid arthritis and systemic lupus erythematosus

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The objective of this study was to clarify possible roles of lymphocyte apoptosis in autoimmune rheumatic diseases. Spontaneous and anti-Fas antibody-mediated apoptosis of peripheral blood (PB) lymphocytes were measured by a flow cytometric method using propidium iodide in primary Sjogren’s syndrome (SS), rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Spontaneous apoptosis levels were significantly higher in 26 SLE patients than in 19 healthy controls. The apoptosis levels were not significantly different between 19 primary SS patients or 28 RA patients and the controls, but high apoptosis levels were observed in some of the patients. The apoptosis of PB lymphocytes was also enhanced in seven SS patients with RA and 16 SS patients with SLE. Anti-Fas antibody could induce apoptosis of PB lymphocytes from both healthy controls and patients’ groups. The antibody-mediated apoptosis levels were higher in RA, SLE and secondary SS patients with RA or SLE, but not in primary SS patients. Each patients’ group was further divided into two groups according to their mean apoptosis levels: patients with high and those with low spontaneous or antibody-mediated apoptosis levels. Clinical variables reflecting disease activity for each disease were then compared between the two groups. Serum rheumatoid factor (RF) and anti-SS-A/Ro antibody titers were higher in the RA or primary SS patients with high spontaneous apoptosis levels than those with low apoptosis levels, respectively. When all the patients’ groups were evaluated together, the spontaneous apoptosis levels negatively correlated with PB lymphocyte counts. In addition, the spontaneous apoptosis levels were decreased by the co-culture of PB lymphocytes with interleukin-2 (IL-2: 100 U/ml) in most individuals including patients and healthy controls. We conclude that spontaneous apoptosis of PB lymphocytes was enhanced in SLE and secondary SS patients. Production of RF or anti-SS-A/Ro antibodies was associated with enhanced apoptosis of PB lymphocytes in RA or primary SS patients. The apoptosis levels were related with lymphocytopenia observed in the patients examined, although various factors including IL-2 seemed to be protective against the apoptosis of circulating lymphocytes. Furthermore, anti-Fas antibody induced apoptosis of PB lymphocytes from the healthy controls and patients, and the antibody-mediated apoptosis levels were high in RA, SLE and secondary SS patients.