Associations of indoor airborne microbiome with systemic inflammation in the context of indoor particulate matter pollution and the metabolic mechanisms

Abstract

Microorganisms constitute an essential component in the indoor environment, which is closely related to human health. However, there is limited evidence regarding the associations between indoor airborne microbiome and systemic inflammation, as well as whether this association is modified by indoor particulate matter and the underlying mechanisms. In this prospective repeated-measure study among 66 participants, indoor airborne microbiome was characterized using amplicon sequencing and qPCR. Indoor fine particulate matter (PM_2.5) and inhalable particulate matter (PM₁₀) were measured. Systemic inflammatory biomarkers were assessed, including white blood cell (WBC), neutrophil (NEUT), monocyte, eosinophil counts, and their proportions. Targeted serum amino acid metabolomics were conducted to explore the underlying mechanisms. Linear mixed-effect models revealed that bacterial and fungal Simpson diversity were significantly associated with decreased WBC and NEUT. For example, for each interquartile range increase in the bacterial Simpson diversity, WBC and NEUT changed by -4.53 % (95 % CI: -8.25 %, -0.66 %) and -5.95 % (95 % CI: -11.3 %, -0.27 %), respectively. Notably, increased inflammatory risks of airborne microbial exposure were observed when indoor PM_2.5 and PM₁₀ levels were below the WHO air quality guidelines. Mediation analyses indicated that dopamine metabolism partially mediated the anti-inflammatory effects of fungal diversity exposure. Overall, our study indicated protection from a diverse indoor microbial environment on cardiovascular health and proposed an underlying mechanism through amino acid metabolism. Additionally, health risks associated with microbial exposure deserve more attention in contexts of low indoor particulate matter pollution. Further research is necessary to fully disentangle the complex relationships between indoor microbiome, air pollutants, and human health.