How does the immune system react to altered gravity?

Space travel has always been a challenge for the human body, especially due to the effects that altered gravity has on biological systems. It has long been known that continued exposure to microgravity conditions human physiology and causes effects that compromise muscular, sensory, endocrine, and cardiovascular functions. Now, is it also risky to expose yourself to altered gravity in short periods?

A new study analyzes the effects that microgravity generated through parabolic flight has on the human immune system. After a brief exposure to altered gravity, everything indicates that there are no significant changes in the defensive capacity of blood cells in the volunteers who participated in the study. In addition, the study authors also found no evidence of aggregation processes in erythrocytes—the cells that transport O2 and CO2 to the cardiovascular system—after the parabolic flight.

The study has been coordinated by Ginés Viscor, Professor of the Department of Cell Biology, Physiology and Immunology of the Faculty of Biology of the University of Barcelona (UB), and the experts Jordi Petriz, from the Germans Trias i Pujol Research Institute (IGTP) have participated ) in Badalona, ​​and Antoni Pérez-Poch, from the Polytechnic University of Catalonia-BarcelonaTech (UPC) and the Institute of Space Studies of Catalonia (IEEC), among other authors. The work has as its first author the researcher Abril Gorgori-González (UB) and has had the support of the Medical Service of the Office of Safety, Health and Environment (OSSMA) of the UB, the Aeroclub Barcelona-Sabadell and the company Thermo Fisher Scientific.

Parabolic flights: a simulated gravity laboratory

Space travel is the ideal scenario to study the effect of microgravity on the human body. They make it possible to study the consequences of a long exposure to microgravity in different astronauts simultaneously, but they require a high cost in time, financing and infrastructure. Without leaving the Earth’s atmosphere, it is also possible to recreate simulated gravity conditions on different platforms. For example, through parabolic flights in aircraft, which make it possible to study the effect of altered microgravity in the short term —even a few seconds— with an affordable cost.

“Artificial platforms such as parabolic flights in airplanes provide valuable results, but are more limited, since they only allow studying the effects of altered gravity in the short term (seconds or minutes). Therefore, the profile of physiological changes that can be recreated with parabolic flights are immediate and transitory changes generated by microgravity on the human body”, indicates Ginés Viscor, head of the Adaptive Physiology Group: Exercise, Hypoxia and Health at the UB.

During the investigation, a twenty-minute parabolic flight was carried out with the Mudry CAP10 light aircraft —a two-seat aerobatic training aircraft— during which fifteen parabolas were flown. “Each parabola makes it possible to reach a period of microgravity for approximately eight seconds, which is followed and preceded by phases of hypergravity of about two seconds”, details the researcher Antoni Pérez-Poch, member of the Department of Computer Science and professor at the School of Engineering of Barcelona East (EEBE) of the UPC and the IEEC.

The microgravity conditions were generated during a short parabolic flight —with fifteen parabolas— in a Mudry CAP10 aerobatic aircraft. (Photo: University of Barcelona. CC BY)

These parabolic flights with an aerobatic plane —a pioneering method in the developed world in Catalonia— were operated by the Aeroclub Barcelona-Sabadell and are the result of aeronautical research carried out in collaboration with the UPC. “This innovative technique has a good ratio of microgravity achieved time compared to maintenance cost, which is very favorable with respect to the increased use of aircraft, although it also has some limitations (logistics and space). In the case of parabolic flights with larger planes, a more expensive operation that has been used since the beginning of the space race by agencies such as NASA or the ESA (European Space Agency), they could reach up to 25 seconds. by parable”, points out Pérez-Poch.

Immune function under pressure

The immediate effects of microgravity on the blood system derive from volume redistribution and blood flow and body fluids to the upper part of the body. “Cardiovascular adaptations consist of an altered cardiovascular response that causes abnormalities in orientation and body balance, a poor response to orthostatic stress, decreased cardiac function, and an inadequate cardiovascular response to exercise,” says Ginés Viscor.

One of the physiological systems most vulnerable to any change in environmental conditions is the immune system, and this is explained by its great plasticity and responsiveness to internal and external imbalances. In the scientific literature, there are still no conclusive results on the immune response to short-term exposure in flights with altered gravity, and in some cases the conclusions are even contradictory.

In this study, the team analyzed the response of the immune system to brief exposure to microgravity based on several parameters: erythrocyte and leukocyte count, hemoglobin concentration, phagocytic capacity and oxidative metabolism.

«The results reveal that the exposure of human blood samples to conditions of altered gravity in parabolic flight did not imply negative effects in relation to the samples that were left on the ground during the experimental work. Neither are significant changes observed in the peripheral blood cell count”, indicates Jordi Petriz (IGTP).

“Except in the case of monocytes —a type of leukocyte— no significant differences have been observed in the functionality of immune cells, either in terms of their oxidative metabolism or in terms of their phagocytic capacity,” stresses researcher Abril Gorgori-González. (UB). “Hypothetically, if there were changes in the functionality of leukocytes when exposed to altered severity, the immune function and defense against external infections or tumor processes would also be compromised.”

The team has applied the technique of acoustically focused flow cytometry with as little manipulation as possible to the volunteers’ blood samples. According to the authors, the typical sample limitation of studies with aerobatic flights —with logistical limitations— does not allow general conclusions to be drawn. For this reason, the objective now is to continue research on the human immune system with other microgravity simulation platforms to study physiological alterations, avoid complications and anticipate risk situations.

Notice for space tourists

Space tourism is an activity of great economic interest for some business sectors. Now, one of the main differences between space tourists and astronauts is the physical and psychological preparation prior to the trip.

“Altered gravity or the constant lack of gravity is one of several changes in the environment that these people who travel to space face. The human body has evolved under the conditions of Earth’s gravity and is therefore not adapted to the absence of this attractive force. In space travel, other factors must be taken into account such as ionizing radiation, constant noise, isolation, confinement, the total distortion of circadian rhythms and brief exposure to extreme temperatures during the return to the atmosphere, “they warn. to the experts.

«Metabolic affectations and long-term osteoporosis and ophthalmological problems have also been described. Although the effect of space travel on people not trained for this type of activity has not been studied, it is possible that all the stressors of the physical environment can negatively affect the health of space tourists. For this reason, “visits in outer space” are designed for now, which are of short duration, “concludes the team.

The study is titled “Effects of rapid gravity load changes on immunophenotyping and leukocyte function of human peripheral blood after parabolic fligh”. And it has been published in the academic journal Acta Astronautica. (Source: UB)