Lost in Space? Unmasking the T Cell Reaction to Simulated Space Stressors

Abstract

The space environment will expose astronauts to stressors like ionizing radiation, altered gravity fields and elevated cortisol levels, which pose a health risk. Understanding how the interplay between these stressors changes T cells' response is important to better characterize space-related immune dysfunction. We have exposed stimulated Jurkat cells to simulated space stressors (1 Gy, carbon ions/1 Gy photons, 1 µM hydrocortisone (HC), Mars, moon, and microgravity) in a single or combined manner. Pro-inflammatory cytokine IL-2 was measured in the supernatant of Jurkat cells and at the mRNA level. Results show that alone, HC, Mars gravity and microgravity significantly decrease IL-2 presence in the supernatant. 1 Gy carbon ion irradiation showed a smaller impact on IL-2 levels than photon irradiation. Combining exposure to different simulated space stressors seems to have less immunosuppressive effects. Gene expression was less impacted at the time-point collected. These findings showcase a complex T cell response to different conditions and suggest the importance of elevated cortisol levels in the context of space flight, also highlighting the need to use simulated partial gravity technologies to better understand the immune system's response to the space environment.

Keywords: altered gravity; space radiobiology; stress immunity.

Figure 1

Space environment hazards astronauts will face in future space missions. Created with BioRender, icons by Freepik.

Figure 2

Main alterations described on T cells in the context of space environment exposure. Decrease in cellular compartments [29]. Cell cycle disruption [30]. Down-regulation of T cell activation [31]. Diminished T cell receptor engagement [32,33,34]. Created with BioRender, icons by Freepik.

Figure 3

Schematic overview of the experimental design with the different experimental conditions of the simulated space stressors in a single and combined manner (green box). HC—hydrocortisone. Created with BioRender, icons by Freepik.

Figure 4

IL-2 measured on Jurkat cells’ supernatant. Measured with ELISA for IL-2 assay and processed with Belysa software (Merck). Values represented are normalized to the control (0 Gy, 0 µM stress, Earth gravity). Plot shows boxplot with median as center line. The bottom and top edges of the box represent the 1st quartile (Q1) and the 3rd quartile (Q3) of the data, respectively. The height of the box (the interquartile range or IQR) represents the middle 50% of the data. The whiskers represent 1.5 times the IQR. The data are divided in different panels based on the addition of stress hormone (stress (µM)) variable comparing the distribution of the normalized IL-2 values across different ionizing radiation exposures (0 Gy, photons, carbon ions). Gravity exposure is represented by different fill colors of the boxes (light green for normal “Earth” gravity, orange for simulated Mars gravity, gray for simulated moon gravity, and light blue for simulated microgravity (“Micro”)). The black line box highlights the control condition, and the horizontal dashed line indicates the average value for the control condition. There are 10–35 replicates per condition. Data analyzed with RStudio v4.3.1”.

Figure 5

t-value ranges and the relationship between coefficient magnitude and significance. A robust linear model was applied to analyze the weighted data of the IL-2 values after exposure to simulated space conditions. In the bar plot, t-values represent the significance of the coefficients for different conditions, while the coefficients’ magnitude indicates the size of the effect each condition has on the response variable. A t-value greater than 1.96 or less than −1.96 is considered statistically significant (marked with *). The color gradient, from red to green, illustrates both the magnitude and significance of the t-values. Red indicates negative t-values, reflecting a negative impact, while green indicates positive t-values, showing a positive impact. The darker the shade, the larger the magnitude of the t-value, emphasizing the strength of the effect. Data analyzed with RStudio v4.31.

Figure 6

IL-2 measured on Jurkat cells using RT-qPCR. Plot shows boxplots with the median as center line. The bottom and top edges of the box represent the 1st quartile (Q1) and the 3rd quartile (Q3) of the data, respectively. The height of the box (the interquartile range or IQR) represents the middle 50% of the data. The whiskers represent 1.5 times the IQR. This figure displays data grouped by stress (µM) exposure on the x-axis and radiation exposure on the facet grid. The y-axis is represented on a logarithmic scale (log IL-2 ddCT) to better visualize a wide range of data values. The gravity factor is represented by fill colors, with light green for normal “Earth” gravity, orange for simulated Mars gravity, gray for simulated moon gravity, and light blue for simulated microgravity (“Micro”). The black line box highlights the control condition, and the horizontal dashed line indicates the average value for the control condition. N = 8 to 28. Data analyzed with RStudio v4.3.1.

Figure 7

In the bar plot, t-values represent the significance of the coefficients for different conditions, while the coefficients’ magnitude indicates the size of the effect each condition has on the response variable. A t-value greater than 1.96 or less than −1.96 is considered statistically significant (marked with *). The color gradient, from red to green, illustrates both the magnitude and significance of the t-values. Red indicates negative t-values, reflecting a negative impact, while green indicates positive t-values, showing a positive impact. The darker the shade, the larger the magnitude of the t-value, emphasizing the strength of the effect. Data analyzed with RStudio v4.3.1.

Figure 8

Three-dimensional scatterplot depicting the correlations (x) between IL-2 gene expression and experimental conditions. The x-axis represents different radiation types, with “0 Gy”, “Carbon ions”, and “Photons”. The y-axis illustrates variations in gravity conditions. Each data point represents a unique experimental setting corresponding to the correlation, with color indicating different stress levels (blue = 0 µM and red = 1 µM). The blue arrow signals the highest correlation value (see also Table 3). Data analyzed with RStudio v4.3.1. This is an interactive plot and can be further explored by assessing the GitHub space: https://silmarilr.github.io/Space_Immune/3D%20Scatterplot%20correlation%20data.html (accessed on 27 November 2023).

Figure 9

Significant simple linear regression for single exposure to simulated space conditions. Black line represents the slope of the curve, and the dotted lines are the 95% confidence intervals. Black dots represent the number of samples. (A,B) Single simulated space stressor exposure; (C,D) Double simulated space stressor exposure; (E) triple simulated sace stressor exposure. IL-2 expression is the ddCT value for IL-2 gene expression. P value is the result of the simple linear regression model, and R squared (R²) reflects the fitness of the model. Data analyzed with GraphPad Prism v10.0.3.