Single-cell transcriptomics reveals the pulmonary inflammation induced by inhalation of subway fine particles.

People generally take the subway and inevitably inhale the fine particles (PM) on subway platforms. This study revealed whether and how subway PM causes lung inflammation. Herein, the pulmonary inflammatory response to subway PM was observed in mice, manifesting as the inflammatory cells infiltration and collagen deposition in tissue, inflammatory cytokine enhancement in bronchoalveolar lavage fluid and Toll-like receptors signal pathway activation in the lungs. Furthermore, single-cell RNA sequencing unearthed subway PM-induced cell-specific responses in the lungs. Twenty immune subsets were identified by the molecular and functional properties. Specific cell populations of CD4 T and γδ T cells were regarded as the predominant sources of pneumonitis induced by subway PM. Moreover, we demonstrated that the lung inflammatory injury was significantly more attenuated in Rag1 mice lacking functional T cells and B cells than that in wild type mice. We proved the slight inflammation of lung tissue in Rag1 mice may be dependent on monocytes and neutrophils by activation of the intracellular molecular network. This is the first experimental study on subway PM causing pulmonary inflammatory damage. It will set an alarm for people who usually travel by subway and efficient measures to reduce PM should be developed in subway stations.