RESUMO
OBJECTIVE: To study the changes of anti-Streptococcus pneumonia (SP) status in rats with simulated weightlessness, and therefore to provide theoretical basis for the aerospace medicine. METHODS: Thirty-two healthy male Wistar rats were randomly allocated into 4 groups: group A, the tail-suspension and SP group; group B, the tail-suspension without SP group; group C, the unsuspended but SP group; group D, the unsuspended and no SP group, with 8 rats in each. The tail-suspension method, i.e. about 30° head-down tilt, was used for the model of simulated microgravity. On day 4, 0.4 ml of SP suspension [ATCC6303, serotype III(ATCC, bacteria concentration about 9.0×108 CFU/ml)] was instilled by tracheal intubation. Sterile saline was used for the control group. The experiment was ended after 7 days of tail-suspension. Lung pathology, blood test and C-reactive protein level were studied, and the CD(4)(+)/CD(8)(+) ratios were measured by flow cytometry. RESULTS: The lung pathological changes were much more severe in Group A as compared to those in Group B, C and D. The total number of WBC showed no significant difference among groups (F = 1.57, P = 0.22). But the neutrophil number was higher in Group A [(2.4 ± 0.53)×109/L], B [(2.0 ± 0.31)×109/L] and C [(1.7 ± 0.40)×109/L] as compared to Group D [(1.2 ± 0.15)×109/L], u = 0.0001, P = 0.001; u = 1.0, P = 0.001; u = 8.5, P = 0.013, respectively. The percentage of neutrophils showed a similar difference. The total number of lymphocytes showed no significant difference among groups (F = 0.720, P = 0.548). CRP levels in the SP infection groups were significantly higher than those in the uninfected groups. The ratio of CD(4)(+)/CD(8)(+) showed no difference among groups (F = 1.225, P = 0.319). Weight loss after the experiment was most severe in Group A (F = 122.067, P < 0.001). CONCLUSIONS: In rats with simulated weightlessness, the anti-infective ability to Streptococcus pneumoniae was reduced, and the inflammatory response was significantly increased, but the anti-infective immunity was compromised.