The association of PM2.5 with airway innate antimicrobial activities of salivary agglutinin and surfactant protein D.

Fine particulate matter ≤2.5 μm (PM2.5) is a prominent global public health risk factor that can cause respiratory infection by downregulating the amounts of antimicrobial proteins and peptides (AMPs). Both salivary agglutinin (SAG) and surfactant protein D (SPD) are important AMPs in respiratory mucosal fluid, providing protection against airway pathogen invasion and infection by inducing microbial aggregation and enhancing pathogen clearance. However, the relationship between PM2.5 and these AMPs is unclear. To better understand the relationship between PM2.5 and airway innate immune defenses, we review the respiratory antimicrobial activities of SAG and SPD, as well as the adverse effects of PM2.5 on airway innate antimicrobial defense. We speculate there exists a dual effect between PM2.5 and respiratory antimicrobial activity, which means that PM2.5 suppresses respiratory antimicrobial activity through downregulating airway AMPs, while airway AMPs accelerate PM2.5 clearance by inducing PM2.5 microbial aggregation. We propose further research on the relationship between PM2.5 and these AMPs.