Dendritic Cell Modification of Neutrophil Responses to Infection after Burn Injury

Burn patients are highly susceptible to infections due to increased exposure through wounds and impairments in a number of immune functions. Dendritic cells (DCs) are important in activation of numerous immune responses that are essential for the clearance of infections. We have found that prophylactic treatment of burn-injured mice with the DC growth factor FLT3 ligand (FL) significantly increases resistance to burn wound infections in a DC-dependent manner that is correlated closely with enhanced bacterial clearance. However, as DCs are not typically microbicidal, the mechanisms by which DC modulation enhances bacterial clearance are not known. Due to the rapid response of neutrophils to cutaneous wounds, and the reported interactions between DCs and neutrophils, we investigated the role of neutrophils in FL-mediated resistance to burn wound infection. This was examined both in vivo and in vitro through neutrophil depletion, supplementation of neutrophils, and assessment of neutrophil chemotaxis following FL treatment. To test the involvement of DCs, CD11c-diphtheria toxin receptor transgenic mice were used to deplete DCs during FL treatment. Studies revealed that neutrophils do play a critical role in FL-mediated resistance to a burn wound infection. Additionally, treatment with FL after a burn injury enhances neutrophil-mediated control of bacterial spread, neutrophil migratory capacity, and myeloperoxidase production in a DC-dependent manner. The results of this study provide new insight into immunological mechanisms that can offer protection against infection after burn injury.