Scientists know that certain factors related to spaceflights may impact the immune system of astronauts, such as microgravity but also radiation exposure, isolation, and stress. Also, a dysregulation occurs in astronauts’ immunity (pro-inflammatory and Th1 responses) during long-term spaceflight. The goal of my study to evaluate the immune system function before, during and after the mission at the MDRS. Blood and saliva samples will be collected from the participants and antibody (IgM, IgD, IgG, IgA, IgE) and cytokine (Th1/Th2/Th17 profiles) production will be measured. Before and after the mission, stimulation assays to study the ability of immune cells, such as neutrophils, B and T cells, to respond to different stimulus will be performed. These biomarkers may be useful to monitor the effectiveness of biomedical countermeasures for astronauts, with potential application in terrestrial research.