Submitted on January 14, 2003
Accepted on August 4, 2003
Distribution and Mitogen Response of Peripheral Blood Lymphocytes Following Exertional Heat Injury
David A DuBose1*, Christian B Wenger1, Scott D Flinn2, Thomas A Judy2, Alexandre I Dubovtsev2, and David H Morehouse1
1 Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts, USA
2 Branch Medical Clinic, Naval Hospital, Beaufort, South Carolina, USA
* To whom correspondence should be addressed. E-mail: david.dubose{at}na.amedd.army.mil.
To determine if immune disturbances during exertional heat injury (EHI) could be distinguished from those due to exercise (E), peripheral lymphocyte subset distributions and phytohemagglutinin (PHA)-stimulated CD69 mitogen responses as discriminated by flow cytometry were studied in military recruits (age, 18.7±0.3 yrs; mean±S.E.) training in warm weather. An E group (3 males; 3 females) ran 1.75-2 miles. During similar E, 11 recruits (10 males; 1 female) presented with suspected EHI. EHI (40.4±0.3°C) vs. E (38.6±0.2°C) body temperature was significantly elevated (p<0.05). Heat illness was largely classified as EHI, not heat stroke, since central nervous system manifestations were generally mild. Blood was collected at E completion or EHI onset (0h), and 2 and 24h later. At 0h (EHI vs. E) suppressor, natural killer and total lymphocyte counts were significantly elevated, helper and B lymphocyte counts remained similar and the helper:suppressor ratio was significantly depressed. By 2h, immune cell dynamics between groups were similar. From 0 to 24h, T-lymphocyte subsets revealed significantly reduced PHA responses (%CD69 and mean CD69 fluorescent intensity) in EHI vs. E. Thus, immune cell dynamics with EHI were distinguishable from E. Since heat stress as reported in exercise or heat stroke are associated with similar immune cell disturbances, these findings in EHI contributed to the suggestion heat stress of varying severity share a common pathophysiological process influencing the immune system.
