Pro-inflammatory effects of airborne particulate matters in relation to biological and chemical composition

Exposure to air pollution has been linked to various adverse health effects, including respiratory diseases, cardiovascular diseases as well as neurological diseases by numerous epidemiological and toxicological studies. Pro-inflammatory effect is suggested to be one of the major mechanisms regarding the health risks posed by pollutants, especially particulate matter (PM). Although the impacts of particle sources and compositions on the discrepancy of elicited inflammation have gained growing attentions, the key determinants remain unclear. Chemical components, i.e., sulfates, nitrates, trace metals, polycyclic aromatic hydrocarbons, have been most closely associated with inflammatory effects. Bioaerosols (short for biological aerosols) including bacteria, fungi, virus, pollen as well as their debris, feature the unique “ligand” properties in activating the receptors of the innate immune cell and evoking inflammation. Nonetheless, with the challenge of identification and characterization of bioaerosols in a real-time manner remaining, there were still limited studies discussing the inflammation induced by bioaerosols. We present a short summary of the pro-inflammatory effects of airborne particles including bioaerosols and chemical composition. Studies on the indispensable role of oxidative stress in promoting cellular inflammatory cytokine production were summarized. Specifically, chemical compositions of PM could affect cellular inflammatory responses via affecting various phosphatase, kinase (e.g., mitogen-activated protein kinase, tyrosine phosphatase), as well as the transcription factors (e.g. NF-κB, Nrf2). Moreover, the role of the PM-borne biological components, e.g. lipopolysaccharide (LPS), was also summarized. Whereas, neither chemical components nor biological components could fully elucidate the PM-induced inflammation. Notably, synergistic effects between PM and allergens were largely discussed with respect to the high prevalence and severity of allergic diseases. Particularly, PM could function as “adjuvant” in elevating the allergic potential of allergens. By taking advantage of this adjuvant function concept, we summarized the past studies on the synergistic effects between chemical and microbial components of particles. Several suggestions are offered for future researches on air pollution-associated health effects: (1) characterize bioaerosols under various weather conditions, aiming to figure out the effects of air pollutants on the airborne microbes; (2) investigate the effects of the interplay between microbial components (e.g., LPS, 1,3-β-glucan) and chemical pollutants (i.e., nitrates, sulfates, organic carbon, elemental carbon, secondary organic aerosols, trace metals, O 3 , NO x , and SO 2 ) on the development of individual inflammation; (3) study the dynamic change of respiratory microbiota, especially under distinct pollution levels, which might give a new clue to uncover the air pollutants-related adverse health effects.