Prolonged Anti-Orthostatic Hind Limb Unloading and Murine Allergic Asthma

Hind limb unloading (HU) is one of the ground-based models of simulated microgravity. As bacterial and viral infections could affect the immune system, the immunologic effect of HU should be studied in a specific-pathogen-free (SPF) laboratory. However, a review of the literature did not reveal any studies on the immunologic effects of prolonged HU in a murine model of allergic disease. Accordingly, the present study was undertaken to evaluate the effect of HU in a murine model of allergic asthma in a SPF laboratory.

Twenty BALB/c mice were allocated equally to Group A (control group), Group B (HU group), Group C (allergic group), or Group D (allergic + HU group). Weight gains, serum total and ovalbumin (OVA)-specific IgE, titers of IL-1, IL-5, IL-10, and IFN-γ in bronchoalveolar lavage (BAL) fluid, and histopathologic findings of the lungs were compared.

After 2 wk of HU, Group D showed significantly more weight loss (-2.0±0.2 g) than Group C (-1.1±0.4 g). Groups B and D showed significant increases in serum OVA-specific IgE as compared with Groups A and C. Group D had significantly lower titers of IL-5 (Group C: 53.0±15.2 pg·ml(-1), Group D: 21.9±13.9 pg·ml(-1)), IL-10 (Group C: 430.8±138.3 pg·ml(-1), Group D: 217.6±51.2 pg·ml(-1)), and IFN-γ (Group C: 104.3±37.5 pg·ml(-1), Group D: 36.7±12.8 pg·ml(-1)) in BAL fluid than Group C. Peri-bronchiolar and pulmonary infiltrations of inflammatory cells were significantly greater in Group D than in Group C.

Prolonged HU may cause significant weight loss and aggravate disease courses.