Objective:To investigate the effect and mechanism of hydrocortisone on circulating T lymphocyte apoptosis in human septic shock. Methods:Total 57 patients with septic shock from January 2006 to January 2009 in Intensive Care Unit of Nanjing First Hospital Affiliated to NJMU were prospectively randomized into treatment groups and control group. Low-dose hydrocortisone was used in treatment group but not in control group. Peripheral venous blood samples of the included patients were obtained to determine the circulating T lymphocyte apoptosis by Annexin V and flow cytometry. At the meantime,the plasma concentration of TNF-α,IL-1β and IL-10 were determined by EASIA. All these results were compared with 20 healthy volunteers and 18 pyemia patients. In the meantime,the difference of septic shock control group and hydrocortisone treatment group was analyzed to investigate the effect of low-dose hydrocortisone on these results. Results:In baseline,the apoptosis percentage of CD4+T lymphocytes in healthy volunteers,pyemia patients and septic shock patients was (4.41±1.45)%,(7.87±3.82)% and (11.01±4.52)%,respectively. And the percentage of Annexin V-positive CD4+ T lymphocytes was higher in septic shock patients than in pyemia patients(P < 0.05),and the later was higher than healthy volunteers(P < 0.05). At the same time, there was no difference in the apoptosis percentage of CD8+ T lymphocytes among these groups(P > 0.05). After treatment of 48 h,the apoptosis percentage of CD4+ T lymphocytes was higher in hydrocortisone treatment group than that in control group,(P < 0.05),while,the apoptosis percentage of CD8+ T lymphocytes had no difference between the two groups(P > 0.05). The plasma concentration of TNF-α in healthy volunteers,pyemia patients and and septic shock patients in baseline was (16.44±9.55)pg/mL,(29.58±13.6)pg/mL and (47.99±25.63) pg/mL respectively. And it was higher in septic shock patients than in pyemia patients(P < 0.05). And the later was higher than healthy volunteers(P < 0.05). After treatment of 48 hours,the plasma concentradtion of TNF-α in hydrocortisone treatment group was lower than that in control group(P < 0.05). The plasma concentration of IL-1β in healthy volunteers,pyemia patients and septic shock patients in baseline was (13.12±5.07)pg/mL,(25.21±14.7)pg/mL and (22.94±22.01)pg/mL respectively. It was higher in pyemia patients and septic shock patients than that in healthy volunteers(P < 0.05). However,there was no difference between the pyemia patients and septic shock patients.(P > 0.05). After treatment of 48 hours,Threr was no difference in the plasma concentration of IL-1β between control group and hydrocortisone treatment group(P > 0.05). The plasma concentration of IL-10 in healthy volunteers,pyemia patients and and septic shock in baseline was(6.38±7.5) pg/mL,(9.67±4.88)pg/mL and(15.01±5.36) pg/mL respectively. It was higher in septic shock than in pyemia patients (P < 0.05). And the later was higher than healthy volunteers(P < 0.05). Forty-eight hours after onset,the plasma concentration of IL-10 in hydrocortisone treatment group was higher than that in control group(P < 0.05). Conclusion:Low-dose hydrocortisone can induce CD4+ T lymphocytes apoptosis when administered in septic shock,and it can also up-regulate the plasma concentration of IL-10. We concluded that IL-10 may be one of the reasons that low-dose hydrocortisone induced circulating CD4+ T lymphocytes apoptosis in septic shock.