Fms-Like Tyrosine Kinase-3 Ligand Attenuates Local and Systemic Infection in a Model of Post-Burn Pneumonia

Burn injury induces immunosuppression and promotes infection with opportunistic pathogens. Pneumonia and sepsis are leading causes of post-burn morbidity and mortality. Fms-like tyrosine kinase-3 ligand (Flt3L) improves local and systemic resistance to P aeruginosa-associated burn wound infection. This study evaluates the effects of post-burn prophylactic Flt3L treatment on local and systemic infection and inflammation in a murine model of pneumonia and sepsis.

Mice received a severe scald burn, were treated with Flt3L or vehicle (CTR) for 5 days, and inoculated trans-nasally with P aeruginosa. Lung, blood, and spleen were harvested at 24 and 48 h postinoculation (p.i.) to assess infection (bacterial burden, bacteremia, distant organ manifestation) and inflammation (interleukin-6 (IL-6) and myeloperoxidase (MPO) levels). Histology correlated infection and inflammation parameters with morphology. Survival at various bacterial concentrations was monitored for 14 days p.i.

Bacterial burden was significantly reduced in lung and spleen of Flt3L-treated mice. Flt3L treatment was associated with decreased signs of pulmonary inflammation (reduced wet weight and IL-6 levels), lower incidences of bacteremia and septic distant organ manifestation, and reduced systemic inflammation (IL-6 and MPO). Histologically, reduced alveolar and peribronchiolar neutrophil and lymphocyte infiltration indicated attenuated pulmonary inflammation after Flt3L treatment. Overall survival was comparable between groups for all doses of P aeruginosa, but mortality delayed in the Flt3L-treated group.

Prophylactic treatment with Flt3L could augment antimicrobial therapy of post-burn pneumonia through improvement of the initial host response to challenge with P aeruginosa, attenuate local, and systemic inflammation as well as septic pathogen dissemination.