**5. Spaceflight as a model of accelerated immunosenescence**

Certain immunological changes observed in astronauts or rodents on space missions can also be found in the elderly. For example, thymus involution, increased susceptibility to infections, and decreased response to vaccines may be correlated with impaired development of B- and T-lymphocyte function in the elderly [78, 79]. This thymus involution and changes in the development and response of immune cells are also observed when the gravitational force is altered, as illustrated by the reactivation of latent viruses in astronauts and the elderly. In addition, a recent study suggests that long-term spaceflight could induce an increase in inflammation as in the elderly (inflammaging), which could increase the risk of allergies or autoimmune diseases in astronauts [80]. Finally, aging is accompanied by changes in antibody production similar to those observed in flight. There is a decrease in antibody affinity [78] and a change in the use of antibody VH gene segments [81] as observed in *P. waltl* immunized in flight [73, 74], which affects the diversity of the antibody repertoire. It therefore appears that stresses encountered during space missions could lead to premature aging of the immune system.
