Transport of microspheres from the lung to the draining lymph nodes by inflammatory monocytes. (APP3P.106)

Inflammatory monocytes (Ly6Chi CCR2hi) play a critical role in steering the course of responses against microbial infections of the lung. Lung monocytes can take up live fungi or bacteria and transport them to draining mediastinal lymph nodes (mLN). How microbes are taken up and trafficked by monocytes from the pulmonary site of infection is poorly understood. To study monocyte-mediated microbial trafficking, we developed a system to trace monocytes that carry particles from the lung to mLNs. Herein, we used mice expressing GFP or the diphtheria toxin receptor under the control of the CCR2 promoter to determine the impact of intratracheally instilled toll-like receptor (TLR) agonists on trafficking of with fluorescent, polystyrene microspheres from the lung to mLNs. This system recapitulates monocyte recruitment and trafficking seen during in vivo infections. Monocytes infiltrated the interstitial space in response to TLR2 agonists. And while neutrophils were the primary cell population associated with instilled microspheres in the lung, they did not deliver them independently to mLNs. Conversely, adoptively transferred monocytes successfully delivered microspheres to mLNs of CCR2+-cell-depleted mice. Our current system and findings empower us to further dissect the process of monocyte uptake of inhaled particles and antigen delivery to lymphocytes of mLNs, which may in turn inform novel vaccine strategies in an age of increasing emergence of antibiotic-resistant pathogens.