Background
Apoptosis of peripheral blood T lymphocytes from patients with Crohn's disease has been described after in vitro activation followed by incubation with infliximab. These ex vivo data raised the question of whether in vivo treatment of rheumatoid arthritis (RA) with the chimeric tumor necrosis factor alpha antibody, infliximab, causes apoptosis in peripheral blood mononuclear cells. This study was designed to detect the early effects of infliximab treatment on apoptosis in the peripheral blood of patients with RA.
Methods
Ten patients with active RA (Disease Activity Score [DAS 28] > 3.2) received 3 mg/kg infliximab intravenously in combination with methotrexate (mean dose of 25 mg weekly). All 10 patients underwent blood sampling before, 1 hour after and 24 hours after the administration of infliximab. Apoptosis was determined using double staining with annexin-V, as an early marker of apoptosis, and 7-amino-actinomycin D (AAD) to exclude necrotic cells from this population. Peripheral blood erythrocytes were lysed and the mononuclear cells were incubated with the different antibodies. The percentages of annexin-V-positive and 7-AAD-negative monocytes and lymphocytes were analyzed by flow cytometry. For statistical analysis, a paired t test was used to compare the percentages of apoptotic cells 1 hour and 24 hours after treatment with those at baseline.
Results
All samples were analyzed for the presence of and change in apoptosis. At baseline, the median percentage of apoptotic monocytes was 0.90% (range 6.23–0.19); 1 hour after treatment, the median percentage was 0.56% (range 2.90–0.32) and 24 hours after treatment the median percentage was 0.21% (range 2.90–0.00). In the lymphocyte population, the median percentage of apoptotic cells was 0.98% (range 2.15–0.00) at baseline as compared with 0.52% (range 6.30–0.00) 1 hour after treatment and 0.39% (range 2.85–0.00) 24 hours after infliximab administration.
Conclusion
In this in vivo study we found no statistically significant increase from baseline in the percentage of apoptotic monocytes or lymphocytes in the peripheral blood of RA patients at 1 hour or 24 hours after infliximab treatment.
Acknowledgement
Supported by Centocor.