Abstract
Recent studies have established that dysregulation of the human immune system and the reactivation of latent herpesviruses persists for the duration of a 6-month orbital spaceflight. It appears certain aspects of adaptive immunity are dysregulated during flight, yet some aspects of innate immunity are heightened. Interaction between adaptive and innate immunity also seems to be altered. Some crews experience persistent hypersensitivity reactions during flight. This phenomenon may, in synergy with extended duration and galactic radiation exposure, increase specific crew clinical risks during deep space exploration missions. The clinical challenge is based upon both the frequency of these phenomena in multiple crewmembers during low earth orbit missions and the inability to predict which specific individual crewmembers will experience these changes. Thus, a general countermeasure approach that offers the broadest possible coverage is needed. The vehicles, architecture, and mission profiles to enable such voyages are now under development. These include deployment and use of a cis-Lunar station (mid 2020s) with possible Moon surface operations, to be followed by multiple Mars flyby missions, and eventual human Mars surface exploration. Current ISS studies will continue to characterize physiological dysregulation associated with prolonged orbital spaceflight. However, sufficient information exists to begin consideration of both the need for, and nature of, specific immune countermeasures to ensure astronaut health. This article will review relevant in-place operational countermeasures onboard ISS and discuss a myriad of potential immune countermeasures for exploration missions. Discussion points include nutritional supplementation and functional foods, exercise and immunity, pharmacological options, the relationship between bone and immune countermeasures, and vaccination to mitigate herpes (and possibly other) virus risks. As the immune system has sentinel connectivity within every other physiological system, translational effects must be considered for all potential immune countermeasures. Finally, we shall discuss immune countermeasures in the context of their individualized implementation or precision medicine, based on crewmember specific immunological biases.
Highlights
The immune system is remarkably complicated, consisting of a myriad of distinct cell populations, each with unique function
Not classical “immune countermeasures” in the sense that they stabilize dysregulated immune function, there are a number of in-place countermeasures that do mitigate clinical risks related to immunity, primarily risk of infectious disease [26]
A discussion of countermeasures must carefully consider the precise nature of the in-flight dysregulation
Summary
The immune system is remarkably complicated, consisting of a myriad of distinct cell populations, each with unique function. The cells of innate immunity react quickly in a non-antigen-specific fashion, whereas cells of adaptive immunity mount a delayed, antigen specific, response that results in long-term memory. The latter includes the distinct humoral and cell-mediated populations, and contains an ever-growing number of distinct cytokine-mediated “biases” of inflammation, including T helper 1 (Th1), T helper 2 (Th2) and T helper 17 (Th17). While reductions in immune cell function may result in increased susceptibility to infectious disease, syndromes of overactive immunity exist, including allergy, asthma, eczema, and autoimmunity. In order to maintain optimal health of its host, the immune system achieves a proper “balance” among its various cell subpopulations, an extreme environment such as space poses a formidable threat to this equilibrium
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