We previously confirmed that high altitude (HA) exposure can modify the number and function of immune cells, leading to a disruption in the homeostatic regulation of T helper1 (Th1)/T helper2 (Th2) immune responses. Our aim was to evaluate possible relationships between the stress response and immunological parameters during HA exposure. Thirteen healthy women spent 21 days at 5050 m. Before (SL1), the first and the 21st day at HA (HA1 and HA2, respectively), and the day after returning at sea level (SL2), we collected blood samples for immunologic parameters, and 24-h urine samples for norepinephrine, epinephrine, and cortisol. Norepinephrine and cortisol significantly increased (p<0.01) at HA1 and HA2 compared to SL1, while epinephrine did not change. At HA1, CD3+ T-cell fell significantly (p<0.001) with respect to SL1, owing to a significant (p<0.001) CD4+ T-cell reduction, while CD16+ and CD56+ increased (p<0.001) at HA2 compared to SL1. The expression of interferon-gamma (IFN-gamma) decreased (p<0.0005) at HA1 and HA2 with respect to SL1. At HA1 different lymphocyte subset (CD3+, CD4+, CD19+) were well correlated with epinephrine (p<0.05), whereas in analyzing the combined data (SL1-HA1-HA2-SL2), CD3+ (r=-0.310), CD4+ (r=-0.332), CD16+ (r=0.404), and CD56+ (r=0.373) demonstrated moderate but significant correlations (p<0.05) with norepinephrine. Moreover, norepinephrine levels were inversely correlated (r=-0.591; p<0.001) with IFN-gamma expression, a typical Th1 cytokine. We suggest that the sympatho-adrenal axis may have a role on the immunologic adaptations observed during HA exposure, and specifically on the observed impairment of the Th1/Th2 immune balance.
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