Pollutant particle priming amplifies airway compartment specific neutrophil and macrophage inflammatory programs...

Real world inhalation exposures occur as temporally staggered mixtures of environmental pollutants and indoor allergens, yet the mechanistic consequences of sequential exposure remain poorly defined. Here, we investigated whether diesel exhaust particle (DEP) exposure primes the lung to alter subsequent responses to house dust mite (HDM) allergen independently of direct co-exposure or preexisting sensitisation. Using a murine model with defined temporal separation between exposures, we combined compartment resolved bulk transcriptomics and targeted single cell profiling to map inflammatory and cellular responses across lung tissue and airway lumen. DEP priming significantly amplified leukocyte recruitment following HDM challenge, with a dominant increase in neutrophils and no corresponding eosinophilic response. Transcriptomic analyses revealed that DEP alone preferentially induced NF-κB associated inflammatory programs, while HDM triggered both NF-κB and interferon (IFN) associated transcriptional responses. Importantly, DEP priming qualitatively reprogrammed the allergen response, enhancing both IFN stimulated gene (ISG) expression and pro-inflammatory cytokine networks. These effects were most pronounced in the airway luminal compartment, indicating a prominent inflammatory niche shaped by recruited immune cells. Single cell analyses identified expansion and activation of multiple neutrophil subpopulations, alongside recruitment of macrophage subsets, NK cells, and CD8⁺ T cells. Ligand receptor inference and protein measurements implicated Cxcl1/Cxcl2-Cxcr2 signalling as a central axis driving neutrophil recruitment, with additional Ccr5 and Cxcr3 linked pathways contributing to broader immune cell infiltration. Ex vivo stimulation suggested that DEP priming enhances intrinsic cellular responsiveness to HDM, in addition to increasing the pool of responsive cells. Collectively, these findings demonstrate that pollutant exposure reprograms airway immune landscapes to amplify subsequent allergen responses, suggested through neutrophil centric and interferon linked mechanisms. This work provides a mechanistic framework for sequential exposure risk, highlights the importance of compartmentalised immune dynamics, and informs the design of advanced in vitro models for respiratory hazard assessment.