Heat Intolerance (HI) is a life threatening deficiency that can lead to heat exhaustion, heat stroke (and possibly death) in a large number of military and civilian occupational groups. We have demonstrated malfunction of transcriptional pathways in the heat stressed HI phenotype and an altered gene expression profile compared to Heat Tolerant (HT) individuals. Such differences are evident even under normothermic basal/comfort conditions. Heat and exercise challenges during the heat tolerance test (HTT) further emphasize the differences between the groups, particularly during recovery at comfort temperatures. Our results indicate that it may be possible to identify markers of heat intolerance. To achieve this goal, we plan to design a cellular (lymphocyte) HTT experimental model and detect gene expression profiles using customized DNA microarrays and bioinformatic tools (the genes selected will be based on our previous DNA microarray studies). Lymphocyte samples collected from HT and HI individuals under resting/comfort conditions will be examined. Treatments and analyses are designed to reveal HI-associated gene-expression profiles (constitutive or inducible), and thereby find lymphocyte markers to identify individuals predisposed to heat injury. The identification of such subjects could prevent unnecessary loss of life. Notably, the rapidly changing climate in our era increases the number of occupation/age groups in which manifestations of HI will appear.

Inclusion Criteria:

• Experienced heat exhaustion or heat stroke in their past
• Participating in heat tolerance tests (HTT)

Exclusion Criteria:

• Unambiguous result of the HTT
• HTT stop by the subject decision

Blood samples of HT and HI subjects will be collected from volunteers who experienced heat exhaustion or heat stroke in their past and participating in heat tolerance test (HTT). The test, using conservative criteria discriminates between HI and HT groups. The distinction between HI and HT groups occurs only following analyses of the HTT.