Purpose: The chronic exposure at high altitude (HA) represents an ideal model for evaluating the in vivo effects of hypobaric hypoxia. Taking advantage of the EV-K2-CNR Pyramid, this study was designed to evaluate whether acute and chronic hypoxia differently modulates the in vivo immune responses.
Methods: The study includes 13 healthy female moderately active volunteers participating to the Italian HA project EV-K2-CNR. Peripheral blood lymphocytes, collected at sea level and at HA in the Pyramid Laboratory of CNR, Nepal (5050 m), were immunologically characterized by flow cytometry and a series of molecular and functional analyses.
Results: Flow cytometric analyses showed that: a) CD3+ T lymphocytes significantly decreased during both acute and chronic exposure to HA, b) T-cell fall was totally due to CD4+ T-cell reduction, c) B lymphocytes were not influenced by the exposure to HA, and d) natural killer (NK) cells significantly increased during acute and chronic exposure. The evaluation of the Th1/Th2 pattern demonstrated a significant decrease of the expression of the Th1 cytokine interferon-γ (IFN-γ) by circulating T cells during acute and chronic exposure to HA. The expression by T cells of CXCR3, a chemokine receptor typically expressed by Th1/Tc1 cells, paralleled the decrease of IFN-γ. On the contrary, the expression of IL-4 was not conditioned by the exposure to HA. Finally, functional studies showed a significant reduction of the proliferative activity in response to mitogen (PHA) both in acute and chronic HA exposure. Despite the increased number of NK cells, NK cytotoxic activity was not influenced by the HA exposure.
Conclusions: Our results indicate that the in vivo exposure to HA leads to an impairment of the homeostatic regulation of Th1/Th2 immune balance that potentially could favor long-term immunological alterations and increase the risk of infections.
1Padua University School of Medicine, Department of Clinical and Experimental Medicine, Clinical Immunology Branch, and 2Sports Medicine Unit, Padova, ITALY
Address for correspondence: Carlo Agostini, M.D., Padua University School of Medicine, Department of Clinical and Experimental Medicine, Clinical Immunology Branch, Via Giustiniani 2, 35128 Padova, Italy; E-mail: firstname.lastname@example.org.
Submitted for publication July 2004.
Accepted for publication November 2004.
This study was carried out within the framework of the EV-K2-CNR “Scientific and Technological Research in Himalaya and KaraKorum” project and in collaboration with the Royal Nepal Academy of Science and Technology (RONAST) as foreseen by the Memorandum of Understanding between the Government of the Kingdom of Nepal and the Government of the Republic of Italy.
This work was supported by a grant of MIUR PRIN 2002 and by contributions from Veneto Region (Italy), the Italian National Research Council (CNR), the National Institute for Scientific and Technological Mountain Research, and the Italian Ministry of Foreign Affairs.