| BackgroundHeat injury is a series of physiological changes and pathological injurys caused by heat stress.Heat cramps,heat exhaustion and heat stroke are all attributable to heat injury.Heat injury always occurs in continuous heat exposure or high-intensitive exercise.It affects both the working efficiency and the health of people who work in heat environment.The mechanism of heat injury is related to the balance between heat production and heat dissipation.When accumulated heat is not able to be dissipated in time,the temperature-regulating center in hypothalamus will fail to function,core temperature will rise,and a mass of blood flow will divert from organs to surface skin.In such a situation,cells of several organs are exposed to ischemia,hypoxia,and hyperthermia injury.Variety of matters activate Inflammatory signaling pathways,and induce the start of systemic inflammation,and excessive expansion of inflammation is the main factor that causes more serious injury.With the progression of heat injury,Multiple Organ Dysfunction Syndrome may happens,which often results in death of the patient.Heat acclimation is the term used to describe the processes occurring when an organism is exposed to environmental heat for a prolonged period.The changes at all levels of body lead to a new homeostasis that is adaptive to heat stress.The risk and severity of heat injury reduces significantly in heat acclimated organisms.The mechanism of heat acclimation is complicated and unclear.A lot of researches show that heat acclimation is able to enhance thermo-tolerance and heat endurance of organisms via reduced basal metabolism,elevated blood volume,improved thermoregulation and cardiovascular function.However,there is no report regarding whether heat acclimation is capable of reducing the level of systemic inflammation by any unclear mechanism during heat stress.In this study,we study the immunocyte subsets in peripheral immune organs and the immunosuppressive Treg cells in heat injury in mice.The purpose is to identify whether Treg cells are protective during heat stress,to investigate the relationship between Treg cells and heat acclimation,and to explore the underlying mechanism.We hope our finding could be helpful in the immunologic mechanism study of heat acclimation.Method1.heat acclimation model in mice were constructed to observe the difference of immunocyte subsets in peripheral immune organs between heat acclimated mice and unacclimated mice.2.Treg cells isolated from spleens and lymphonodus of C57/BL6 mice were transferred into other C57/BL6 mice by tail vein injection.Mortality and injury of treg cells-transferred mouse were evaluated after heat stress,to determine the correlation between Treg cells and level of heat injury.3.mortality and injury level were evaluated after heat shock experiment between C57/BL6 mice and Mir-155-/-mice.The objective is to identify whether Thermo-tolerance reduces in Treg-deficiency mice.4.Flow cytometry was used to assay the frequency of Treg cell in heat acclimated mice and.unacclimated mice.The frequency of neutrophils in peripheral circulation were measured,The frequency of neutrophils and Tregs were also detected to clarify the correlation between Treg cells and neutrophils.5.Cell co-culture experiment and immunohistochemistry were carried out to investigate the mechanism that heat acclimation enhance Thermo-tolerance of mice.Result1.The analysis of immunocyte subsets showed a significant elevating of Tregs in spleen and lymphonodus after heat acclimation.2.Comparison between heat acclimated mice and unacclimated mice under heat stress showed a significant difference in mortality and organ injury,indicating that Treg cells contribute to lower level of heat injury.3.Treg-transferred mice had lower mortality and lower level of organ injury,indicating that increase of Tregs in mice is a protective factor under heat stress.4.Mir-155-/-mice had higher mortality and more severe organ injury under heat stress,suggesting that decrease of thermo-tolerance in Mir-155-/-mice is related to defective Treg cells.5.Correlation analysis between Treg cells and neutrophils in spleen revealed a negative manner.We conclude that Treg cells could regulate the recruitment of neutrophil in acute inflammation,and reduce the level of heat injury.6.Result of immunohistochemistry showed that expression of PD-L1 and Foxp3 were both enhanced in spleens and livers in heat acclimated mice,indicating that heat acclimation may up-regulate expression of PD-L1 and Foxp3,which plays an important role in maintaining activity of Treg cells and promoting differentiation of Treg cells.7.The result of cell co-culture experiment showed that activated Tregs were able to suppress the secretion of myeloperoxidase,indicating that activation of neutrophils were depressed.Tregs may inhibit the activation of neutrophils under heat stress to a certain degree by Regulating PD1/PD-L1 signaling pathway.ConclusionTo a certain extent,our study uncovered a part of immunologic mechanism through which heat acclimation enhances thermo-tolerance.It is closely associated with the immune negative regulation of Treg cells.Heat acclimation may induce the up-regulation of Treg cells in peripheral immune organs,and decrease the recruitment of neutrophils in acute inflammation in heat injury.The mechanism that Treg cells increase in heat acclimated mice may involve the up-regulation of PD-L1 and Foxp3.Tregs may inhibit the activation of neutrophils under heat stress to a certain degree by Regulating PD1/PD-L1 signaling pathway. |
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