Myeloid-derived interleukin-10 induced by thrombospondin-1 mediates host defense and regulates inflammation during acute bacterial lung infection

<i>Pseudomonas aeruginosa</i> (<i>P. aeruginosa</i>) is a leading cause of hospital- and ventilator-associated pneumonia, driven by virulence factors that damage lung tissue. Neutrophils and monocytes are myeloid immune cells that play key roles in host defense during pulmonary infection against <i>P. aeruginosa</i>; although if not properly regulated, their inflammatory activity can lead to severe lung injury. Thrombospondin-1 (TSP-1) is a host glycoprotein that regulates neutrophil activation in the lungs during <i>P. aeruginosa</i> infection, protecting the host from mortality. Here, we demonstrate that in addition to regulating the pro-inflammatory phenotype of neutrophils, during <i>P. aeruginosa</i> infection, TSP-1 induces IL-10 in the lung tissue of mice inoculated with this bacterium. Our data show that neutrophils and Ly6C⁺ monocytes are major sources of lung IL-10 during the first 48 h post-infection, a cytokine that is required for host survival, host defense, and to reduce lung inflammation and injury. Further <i>in vitro</i> studies determined that TSP-1 induces IL-10 production in lipopolysaccharide-stimulated CD11b⁺Ly6G⁺Ly6C⁺ cells differentiated from bone marrow precursors through a mechanism dependent on the transcription factor peroxisome proliferator-activated receptor gamma (PPARγ). Importantly, intratracheal transfer of <i>IL-10^+/+</i> CD11b⁺Ly6G⁺Ly6C⁺ cells 1 day before infection to <i>Thbs1^-/-</i> mice restored their ability to produce IL-10 in the lungs, improved host defense, and reduced lung inflammation and permeability upon infection. Altogether, our data show that TSP-1 induces IL-10 production in neutrophils and monocytes, enhancing host defense while reducing lung inflammation.