Immune responses in adult female volunteers during the bed-rest model of spaceflight: Antibodies and cytokines

Background: It is unknown whether a prolonged period of bed rest will affect human immune responses, particularly in female subjects. Objective: We sought to measure immune responses in adult female subjects exposed to prolonged bed rest. Methods: Adult (25-40 years) female volunteers (n = 24) were maintained in a supine (6 degrees tilt) head-down bed-rest (HDBR) position for 60 days: 8 with HDBR only, 8 with HDBR and regular muscular exercise, and 8 with HDBR and dietary protein supplementation. Subjects were immunized with bacteriophage phi X-174. Antibody production and plasma cytokine levels were determined. Results: The rate of primary antibody production of the HDBR plus exercise group increased faster (P = .01) and to a higher level versus that of the HDBR-only group (P = .03) and that of the HDBR plus diet group (trend P = .08). The rates of secondary antibody production between the 3 groups were similar, but the level of antibody in the HDBR plus exercise group remained higher versus that in the HDBR-only group (P = .03). Both the HDBR (P = .001) and HDBR plus diet (P = .02) groups had time-related progressive increases in TNF-alpha receptor levels, but the HDBR plus exercise group remained at baseline. The HDBR plus exercise group experienced an acute increase in IL-1 receptor antagonist levels versus the HDBR (P = .02) and the HDBR plus diet (P = .02) groups, with similar increases in RANTES levels. Conclusions: The exercise countermeasure accelerated primary antibody production and increased antibody levels to bacteriophage phi X-174 and also opposed the potentially harmful effects of increased TNF-a levels caused by prolonged bed rest, possibly by activating the anti-inflammatory cytokine IL-1 receptor antagonist and the chemotactic factor RANTES. (J Allergy Clin Immunol 2009;123:900-5.)