Immunity in Space: Prokaryote Adaptations and Immune Response in Microgravity

Abstract

Immune dysfunction has long been reported by medical professionals regarding astronauts suffering from opportunistic infections both during their time in space and a short period afterwards once back on Earth. Various species of prokaryotes onboard these space missions or cultured in a microgravity analogue exhibit increased virulence, enhanced formation of biofilms, and in some cases develop specific resistance for specific antibiotics. This poses a substantial health hazard to the astronauts confined in constant proximity to any present bacterial pathogens on long space missions with a finite number of resources including antibiotics. Furthermore, some bacteria cultured in microgravity develop phenotypes not seen in Earth gravity conditions, providing novel insights into bacterial evolution and avenues for research. Immune dysfunction caused by exposure to microgravity may increase the chance of bacterial infection. Immune cell stimulation, toll-like receptors and pathogen-associated molecular patterns can all be altered in microgravity and affect immunological crosstalk and response. Production of interleukins and other cytokines can also be altered leading to immune dysfunction when responding to bacterial infection. Stem cell differentiation and immune cell activation and proliferation can also be impaired and altered by the microgravity environment once more adding to immune dysfunction in microgravity. This review elaborates on and contextualises these findings relating to how bacteria can adapt to microgravity and how the immune system subsequently responds to infection.

Microbes and Space Travel – Hope and Hazards

“…Under both simulated microgravity environment as well as on board spaceflights and the International Space Station, bacteria have been shown to undergo novel mutations to adapt to this unique environment [26,27]. Some of these adaptations to space flight alter the pathogen life cycle, some confer tolerance to harsh environments (e.g.…”

“…These variable adaptations are likely to be dependent on environmental conditions, as well as specific bacterial strains [26,27]. Some of these adaptations may become more permanent with time, thus raising the possibility of their inadvertent introduction into the wider bacterial flora on Earth upon return [27,28].…”

“…These variable adaptations are likely to be dependent on environmental conditions, as well as specific bacterial strains [26,27]. Some of these adaptations may become more permanent with time, thus raising the possibility of their inadvertent introduction into the wider bacterial flora on Earth upon return [27,28]. Such introductions may lead to more severe infections in individual patients, but also larger, more severe outbreaks in the population of these 'space-enhanced' pathogens [27].…”

“…Some of these adaptations may become more permanent with time, thus raising the possibility of their inadvertent introduction into the wider bacterial flora on Earth upon return [27,28]. Such introductions may lead to more severe infections in individual patients, but also larger, more severe outbreaks in the population of these 'space-enhanced' pathogens [27]. Yet other studies suggest that there is currently no clear, consistent or definitive evidence that these adaptations pose actual risks to the health of space travellers either inflight or upon their return to Earth [28,29].…”

The Effects of Simulated Microgravity on Macrophage Phenotype

“…Among the cell types being evaluated, immune cells are of particular interest due to their critical role in pathology and human health [ 5 , 6 ]. There are well documented reports of humans experiencing viral shedding while in space, which further motivates studies to assess the effect of space flight on immune cells [ 7 , 8 , 9 ]. Macrophage immune cells are present in the majority of tissues throughout the body and are involved in immunological functions as well as tissue remodeling.…”