Immunology is one of eleven International Bedrest Standard Measures conducted on healthy subjects at the :envihab facility in Cologne, Germany. Immune system dysregulation during spaceflight is well characterized and may result in specific clinical risk to crewmembers participating in exploration class space missions. Casual factors for this phenomenon may include microgravity, physiological stress, isolation, altered nutrition, and disrupted circadian rhythms. The appropriateness of a bed rest analog to demonstrate impacts on the immune system is inconclusive. There are some isolation and fluid shifts associated with bed rest which could influence the immune system.
A complete blood count and basic leukocyte subsets indicate constitutive immune activation for an individual subject. Concurrent with any functional dysregulation, it is important to know if a subject’s current immune system remains within baseline values. Stress hormone levels provide an important physiological indicator regarding subject adaptation to the space-analog condition. Globulin fractionation is also an indicator of dysregulation in plasma protein concentrations, which may correlate with constitutive immune activation or inflammatory processes. Plasma immunoglobin G (IgG) levels are also an indicator of constitutive immune activation, specifically humoral immune responses. Viral antibody levels however, are an indicator of latent herpes virus reactivation. Latent viral reactivation is associated with immune suppression both terrestrially and during spaceflight.
The purpose of the standard measures project is to populate a repository with data that enables high-level monitoring of countermeasure effectiveness and meaningful interpretation of health and performance outcomes. The :envihab standard measures will support future, hypothesis-driven research that enables planetary missions by providing an optimized minimal set of measures captured from subjects. These measures will be available to other studies under data sharing agreements as well as undergo analysis to understand risk posture.
Analysis of basic leukocyte subsets will be performed by flow cytometry. Whole blood samples will be stained using the appropriate fluorescent-labeled monoclonal antibodies relevant for the leukocyte subsets of interest. Following leukocyte staining, red blood count will be lysed using any of several accepted methods. The stained leukocyte will be fixed prior to analysis. Flow cytometry analysis will include bead-based validation of instrument optical precision, appropriate positive/negative controls, as well as controls to verify the absence of spectral overlap. Stress hormone levels in plasma or serum as well as plasma concentration of IgG and antibodies for specific latent herpes viruses will be measured using competitive binding enzyme-linked immunosorbent assay (ELISA). Serum globulin electrophoresis will be used to analyze serum globulins levels, concentrations of alpha 1 globulin, alpha 2 globulin, beta globulin, and gamma globulin.
The scheduled days of collection are as follows:
The :envihab International Bedrest Standard Measures Test Battery is not a hypothesis-driven study, but rather a collection of data made available to future researchers and for trend analysis. As such, there are no specific hypotheses, outcome measures, or statistical analyses associated with the skeleton of the project. The questionnaire will capture a "snapshot" of optimized data that can be investigated by researchers in the future.
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