Countermeasures for ameliorating in-flight immune dysfunction.

We analyzed immune disturbances caused by the influence of spaceflight factors and proposed approaches for their correction. First, we determined the significant resistance of humoral immunity to the action of spaceflight factors, for example, B cell and immunoglobulin content, B cell reactivity to lipopolysaccharide, and distribution of B cell clones to trinitrophenyl (TNP group). A brief reversible increase of IgA and/or IgG concentration was the most characteristic shift observed. However, we noted prominent changes of T cells and natural killer (NK) cells, such as decreases in the content and phytohemagglutinin (PHA) reactivity of T lymphocytes, reduced T helper activity, and a reduction in NK cell cytotoxic activity in humans and animals during prolonged, spaceflights. Rat bone marrow cells showed a decreased response to macrophage colony-stimulating factor. Studies with rat lymph node cells showed that microgravity and spaceflight stressors may influence lymphocytes in a tissue-specific manner. In experiments on isolated cells, human lymphocytes produced interferon more intensively in a reduced-gravity (microgravity) environment than under terrestrial conditions. However, lymphocyte activation by concanavalin A was sharply suppressed. Under microgravity conditions the transfer of activating signal to protein kinase C was strongly reduced. Thus, in-flight disturbances of T and NK cell functions are quite significant and could cause some diseases. However, to date the in-flight immune dysfunctions have not been excessive. Probably, we are mainly dealing with a complex of changes of immunity in space that is similar to that in the presence of acute stress. Therefore, it is reasonable to consider stress-related immunotherapy approaches in the practice of space medicine. The most effective methods and approaches of modern immunotherapy, such as artificial vaccines, monoclonal antibodies and immunoconjugates, recombinant cytokines, or immunomodulators etc, are also reviewed.