Abstract: ObjectiveTo study changes of the apoptosis of polymorphonuclear neutrophil at early postburn stage in rats and the interventional effects of low-does cyclophosphamide. Methods　110 SD-rats were divided into 3 groups randomly: experiment group(model+low dose of CY,n=50),burn group(model,n=50) and normal group(n=10). Drugs were injected into abdominal cavity immediately after burn , bone marrow and blood samples were obtained in the 3th,6th,12th,24th and 48th h.The apoptosis of PMN in the bone marrow and blood was analyzed by FCM. Results The apoptosis rate of PMN in the bone marrow: increased in burn group from 6th h (p<0.05), peaking at 12th h, cutted down from 24th h.; increased in CYgroup from 6th h (p<0.05),and continued to increase at 48th h.. CY group was compared with burn group , increased at 24th h. and 48th h. (p<0.05). The apoptosis rate of PMN in the blood : cutted down from 6th h (p<0.05),and to 48th h in burn group; cutted down from 6th h (p<0.05),and to 48th h in CY group; CY group was compared with burn group , increased at 6th h、12th h (p<0.05).Conclusion The low dose of CY could promote PMN apoptosis of the bone marrow and blood at early postburn stage. It could influence the development of burn SIRS.

Key words: Burn, Bone marrow, polymorphonuclear neutrophil, apoptosis, cyclophosphamide