Trauma-induced lung injury is associated with infiltration of activated TLR expressing myeloid cells

Introduction: Traumatic injury with hemorrhage (TH) induces an inflammatory response in the lung resulting in lung injury involving activation of immune cells including myeloid cells (i.e., monocytes, granulocytes and macrophages), in part through TLRs. TLRs, via the recognition of damage associated molecular patterns (DAMPs), are a key link between tissue injury and inflammation. Nonetheless, the role of TLRs in myeloid cell activation and TH-induced lung injury remains ill defined. Methods: C57BL/6 male mice were subjected to TH or sham treatment (n = /group). Lung tissues were collected two hrs. after injury. Single cells were isolated from the lungs by enzymatic digestion and myeloid cell TLR expression and activation (i.e., cytokine production) were assessed using flow cytometry techniques. Results: The injury was associated with a profound change in the lung myeloid cell population. TH markedly increased lung CD11b(+) monocyte numbers and Gr1(+) granulocyte numbers as compared to sham mice. The number of cells expressing TLR2, TLR4, and TLR9 were increased 4-7 fold in the TH mice. Activation for elevated cytokine (TNF alpha, IL-10) production was observed in the lung monocyte population of the TH mice. Conclusions: Trauma-induced lung injury is associated with infiltration of the lungs with TLR expressing myeloid cells that are activated for elevated cytokine responses. This elevation in TLR expression may contribute to DAMP-mediated pulmonary complications of an inflammatory nature and warrants further investigation.

Automated summary

The study found that traumatic injury with hemorrhage leads to lung injury, activation of immune cells, and elevated cytokine production in the lungs. These cells play a key role in mediating inflammatory responses through TLRs.