| The incidence of infection after severe injury (AIS>3)is extremely high. Many scholars find that severe injury bring about restrain of immune function. There are multiple changes in body immune function in acute stage of severe injury, such as the quantitative and functional descent of CD4, CD4 / CD8 ,while the increase of CD8. Interleukin 2 (IL-2) mostly comes from CD4 and CD8 T lymphocytes and has an important role in immune response and immune regulation. Tumor necrosis factorα(TNF-α) has extensive biologic activity and is often involved in inflammatory reaction and immune response. Immunoglobulin has antibody activity and has a function in anti-infection of humoral immunity. It exists with form of IgG in body. So the level of IgG generally can reflect the humoral immunity state.It is acceptable that the use of mild hypothermia therapeutics(32℃～35℃) in patients with trauma, especially severe craniocerebral trauma. Many reports confirmed brain safety effect of mild hypothermia without serious adverse effect in the past two decades. The mechanism of mild hypothermia therapeutics applicated in severe injury and body protection is not clearly explained. Some reports suggest that total body hypothermia after trauma and blood loss can decrease metabolic rate, soften tissue damage, repress inflammatory reaction, extend"golden time"of emergency treatment and elevate survival. The effect of mild hypothermia therapeutics on immune system after severe injury has not been elucidated. To investigate the influence of therapic mild hypothermia on immune function, rats with hemorrhagic shock induced by severe injury were used as model.MethodsIn this study, sixty SD rats ( weight: 200~300g, female and male) were randomly divided into three groups, ten died in experiment. Control group(group1); normal body temperature group (group2), examined at 6h and 24h; mild hypothermia group (group 3), examined at 6h and 24h. Except group 1, other two groups were the trauma and hemorrhagic shock model. Hemorrhagic shock was induced in forty adult rats to a mean arterial pressure of 40 mmHg. Hypotension was maintained for one hour, resuscitation was accomplished with the shed blood and lactated Ringer's solution (2×blood volume). Intrarectal temperatures were measured replacing the central temperature (CT). The normal contro1 group used broiling lamp to maintain intrarectal temperature at 38～39℃; while The mild hypothermia therapeutics group used ice water to reduce the temperature and the intrarectal temperature was maintained at 32.5～33.5℃. The rats were executed at 6h and 24h through bloodletting in the abdominal aorta. Add 4ml blood plasma into heparinized centrifuge tube and centrifugalize. Keep the supernatant fluid at -20℃for measuring immunoglobulin IgG.1.6ml blood plasma was used for determining the subsets of T lymphocyte. Cell factors IL-2 and TNF-αwere examined using ELISA.Results1. The expression of CD4 and CD4/CD8 ratio obviously decreased, the expression of CD8 heightened in peripheral blood of rats with trauma and hemorrhagic shock. Compared with normal body temperature group, the expression of CD4 and CD4/CD8 ratio increased (P<0.01)while the expression of CD8 decreased significantly(P<0.05) in mild hypothermia therapeutics group in both 6h and 24h treatment condition.2. The expression of cell factor IL-2 lowered and TNF-αheightened in trauma and hemorrhagic shock models. Compared with normal body temperature group, the expression of IL-2 increased (P<0.01)while TNF-αdecreased significant (P<0.05)in mild hypothermia therapeutics group in both 6h and 24h treatment condition.3. The expression of immunoglobulin IgG of peripheral blood had no significant change(P>0.05)between normal contro1 group and mild hypothermia therapeutics group.4. The rats in normal contro1 group were all survival, while few of the rats in each experiment group died and the rate of death had difference but had not statistically significant(P>0.05).Conclusion1. In the early stage of trauma and hemorrhagic shock, the cellular immune function is repressed, CD4, CD4/CD8 and IL-2 all decrease obviously and inflammatory mediators such as TNF-αelevate .The application of mild hypothermia therapeutics can improve and stabilize cell immune function. 2. In the early stage of trauma and hemorrhagic shock, humoral immunity changes little even in the state of using mild hypothermia therapeutics.3. Although the use of mild hypothermia therapeutics can improve cell immune function, the early survival has no notable elevation. The effect of mild hypothermia on trauma is in many ways and has multifactor, which needs further study.
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