Rehydration does not affect pulmonary immune responses to influenza or susceptibility to secondary bacterial pneumonia
KeywordsInfluenza Streptococcus Pneumoniae Influenza Infection Bacterial Pneumonia Sodium Lactate
In our murine model of influenza, significant weight loss occurs up to day 7 post-infection . We sought to determine whether weight loss from influenza could be altered by rehydration and whether this affects pulmonary immune responses.
Adult BALB/c mice were infected with X31 (H3N2) influenza (1:80) via the intranasal route and randomized to intraperitoneal rehydration with 20 ml/kg compound sodium lactate (CSL), normal saline (NS) or no rehydration (NR) starting on day 3 following infection and continued for 4 days (n = 5/group). On day 7, mice were challenged with 1 × 106 Streptococcus pneumoniae (serotype 2). Two further cohorts of mice were challenged with different doses of influenza and rehydrated from day 3 to 7 to investigate pulmonary immune responses in the absence of bacteria. Mice were infected with 1:80 (n = 10/group) influenza and rehydrated once daily or 1:60 (n = 5/group) influenza and rehydrated twice (1:60) daily with 20 ml/kg CSL or not. Daily weight, survival following secondary bacterial pneumonia, number of colony-forming units (48 hours after bacterial challenge) from peripheral blood, lung, and nasal wash and cellularity in lung compartments were measured.
Rehydration did not affect weight loss following 1:80 influenza infection (naïve mice (+0.3 ± 0.4 g), influenza plus NR (-1.58 ± 0.4 g), influenza plus CSL (-1.1 ± 0.7 g) and influenza with NS (-1.3 ± 0.4 g)). A repeat experiment with CSL once daily or twice daily did not alter weight loss compared with NR (P > 0.05). Survival or CFU counts following bacterial pneumonia did not differ between the groups (P > 0.05). The total number or activational status of bronchoalveolar, lung macrophages/monocytes and lymphocytes was not affected by rehydration following influenza infection or 48 hours following bacterial pneumonia (P > 0.05; P < 0.05 vs naïve mice).
Rehydration does not affect immunity or pathophysiology in a murine influenza infection model. Assuming these results can be extrapolated to the clinical setting, our findings support the use of conservative fluid resuscitation strategies in patients with influenza.