Increased susceptibility to apoptosis in circulating lymphocytes of critically ill patients

Abstract.

Background and aims: Lymphocyte apoptosis may influence immune responsiveness in systemic inflammation. Therefore, we investigated whether early signs of apoptosis (i.e., annexin-V binding and cell shrinkage) in peripheral lymphocytes were different among patients with severe sepsis, critically ill, nonseptic patients after major surgery, and healthy individuals. Patients/methods: Ten patients with severe sepsis and ten critically ill, nonseptic patients after major surgery admitted to a surgical intensive care unit in a university hospital were included in the study. In addition, ten healthy blood donors were included for comparison. We investigated early signs of apoptosis using flow cytometric measurement of annexin-V binding to the cell surface and cell shrinkage of peripheral lymphocytes. Results: The percentage of apoptotic lymphocytes determined as annexin-V positive and propidium iodide negative cells was increased in freshly prepared cells of patients with severe sepsis (11.4±0.5%) and critically ill, nonseptic patients after major surgery (18.5±2.0%) relative to healthy blood donors (4.4±0.5%) (P<0.05). No significant difference between patients with severe sepsis and patients after major surgery were found. Annexin-V binding increased significantly after OKT-3 stimulation of lymphocytes in patients with severe sepsis (34.4±1.6%), patients after major surgery (33.8±3.4%), and healthy blood donors (21.1±2.8%). No significant difference among groups was detected following OKT-3 stimulation. Furthermore, freshly isolated peripheral lymphocytes of patients with severe sepsis and critically ill, nonseptic patients after major surgery revealed a significantly higher proportion of cell shrinkage than in healthy blood donors (55.0±2.2%, 21.5±2.4% vs 3.6±0.7%; P<0.05). Conclusion: Circulating lymphocytes of critically ill patients show a high degree of early signs of cellular apoptosis. This may contribute to hyporesponsiveness of immune cells in systemic inflammation.