Sepsis is characterized by the increases in percentages of circulating CD4⁺CD25⁺ regulatory T cells and plasma levels of soluble CD25

The function of immune system is to protect hosts from invading microorganisms by destroying infected cells while minimizing damage to tissues. Among immune cells, CD4⁺CD25⁺ regulatory T cells (Treg cells) control immune responses by limiting infectious processes. However, it remains unclear whether Treg cells are induced in systemic inflammatory response syndrome (SIRS) or infectious SIRS (i.e. sepsis). SIRS and sepsis arc associated with stressful inflammatory conditions. We therefore measured CD25⁺ T cells and circulating CD4⁺ T cells, along with plasma levels of CD25, interleukin (IL)-6, and IL-10, in 20 septic patients (64 ± 11 years), 16 SIRS patients (59 ± 16 years), and control subjects: 13 elderly (60 ± 16 years) and 14 young volunteers (28 ± 3 years). Septic patients (23.3 ± 11.8%, p < 0.01) showed significantly higher percentages of CD25⁺ cells among CD44^T cells (i.e. Treg cells) than did either young (10.6 ± 3.7%) or elderly volunteers (11.1 ± 3.8%). The percentages of Treg cells in septic patients were higher than those in SIRS patients (12.4 ± 6.9%, p < 0.01). Moreover, plasma levels of soluble CD25 were significantly higher in septic patients, compared to the levels in SIRS patients or volunteers (p < 0.01). No significant difference in plasma levels of IL-6 or IL-10 was found between septic patients and SIRS patients. Thus, sepsis is associated with the increased percentages of Treg cells and elevated plasma level of soluble CD25. The elevation of these parameters might be a useful marker of infections in SIRS.