Immune system

Abstract

The human immune system is a complex network of molecular, cellular, and genetic components designed to provide defense against foreign organisms and substances. It is a highly regulated system that is sensitive to a number of extrinsic factors including environmental stress (e.g., heat, cold, microgravity, and hypoxia). The impact that any stressor is likely to have on immune function is dependent on whether the stress is acute or chronic, the severity of the stress, and the individual's current physiological and emotional state. While the effects of hypoxia on the immune system are evident at almost all levels and so will have potential impact on infectious risks and outcomes, high altitude and hypoxia also affect certain pathogens and their vectors to alter human health at high altitude. We will review how hypoxia affects the innate and adaptive immune systems both positively and negatively, and the central role of hypoxia inducible factor(s) (HIF) in these changes, how the central nervous system (CNS) contributes particularly to the adaptive immune responses at high altitude, and how these responses affect aspects of defense against pathogens, vaccine effectiveness, and immunosurveillance of cancer.