Immune responses and latent herpesvirus reactivation in spaceflight

Background: Increased frequency and severity of herpesvirus infections are common in individuals with impaired cellular immunity, a phenomenon observe d in both the elderly and astronauts alike. This study investigated immune responses and latent herpesvirus reactivation during a 9-d spaceflight. In addition, adrenocortical and immune responses of an elderly astronaut (payl oad specialist-2, PS2; age 77) who flew on this mission were compared with that of younger crewmembers. Hypothesis: Spaceflight and associated stresse s will decrease cellular immunity and reactivate latent herpesviruses. Meth ods: Blood and urine samples, collected from the seven crewmembers who flew on the Space Shuttle Discovery (STS-95), were analyzed for levels of neuro endocrine hormones, leukocyte and lymphocyte subsets, and evidence of herpe svirus reactivation. Results: Prior to flight, increased antibody titers to latent Epstein-Barr virus were found. During flight, acute changes in dehy droepiandrosterone sulfate (DHEAS) and cortisol resulted in a pronounced de crease in the DHEAS/cortisol ratio by the end of the mission for PS2 and a younger crewmember. Shedding of cytomegalovirus (CMV) in urine and increase d CMV antibody titers also occurred inflight. At landing, the percent incre ases in adrenocorticotropic hormone and cortisol were greatest for PS2 as c ompared with the other six crewmembers. A significant neutrophilia also was observed in all crewmembers. Notably, PS2 had large increases in monocytes and natural killer cells at landing while other crewmembers showed little change or a decrease. Conclusions: These findings indicate that spaceflight and associated stresses reactivate latent herpesviruses and suggest that a cute changes in neuroendocrine hormones mediate these changes in part by do wnregulating cellular immunity. Moreover, the similarities between aging an d spaceflight suggest that the study of the immune system in elderly subjec ts may be useful as a predictive model for astronauts enduring long-term sp aceflights.