Indoor PM10 Upregulates Pro-inflammatory Mediators in Bronchial Epithelial Cells

Indoor dusts are collectively formed from anthropogenic and atmospheric activities. Particle matter 10 (PM10) is inhalable and causes significant inflammation by interaction with the pulmonary epithelial barrier. The mediators involved in bronchial epithelial cells response to dust are remined unknown. The air-liquid interface of our lung on chip model was exposed to indoor dust collected from highly polluted houses in Delhi, India. The media were collected after 4 days and cytokine levels were measured. We found that the concentration of IFN, IFNγ, Interleukin-6 (IL-6), IL1b, TNFa, and Granulocyte monocyte colony stimulating factor (GM-CSF) were significantly increased after exposure to indoor dust. IFN type I pathways were a major response from dust exposure. Further investigation is needed to determine the mechanism of action and targets of dust in bronchial epithelial cells.


Introduction
Indoor exposure to aerosolized particulate matter up to ten micrometers in size (PM10) is a significant respiratory health concern, especially in urban environments and in low-middle income countries with poor air quality [1]. Indoor PM10 may come from indoor activities like cooking, or it may be transported from outdoor air pollution [1,2]. In fact, PM10 is spatially and temporally correlated to outdoor anthropogenic activity [2]. During inspiration, PM10 is brought into the respiratory tract through airflow convection. Given its size, ≤ 10μm in aerodynamic diameter, PM10 deposits in bronchial airways through sedimentation or inertial impaction leading to the subsequent development of pulmonary disease [3]. The link between increased air pollution and the development of pulmonary pathology is attributed to direct oxidant release from organic and metal components as well as indirect oxidative cellular responses. Production of reactive oxygen species and oxidative stress initiates an inflammatory cascade leading to cellular apoptosis [4]. PM10 penetrates the mucosal layer of bronchial airways leading to localized epithelial damage which is subsequently amplified by cytokine production [5].
Interferon- is a type I interferon (IFN 1) implicated in regulation of inflammation in viral infections and immune disorders [6]. Recently, we investigated the role of Mycobacterial cell wall microparticles on normal human bronchial epithelial (NHBE) cells and found a differential Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 14 August 2020 doi:10.20944/preprints202008.0315.v1 overexpression of IFN 1 pathway proteins and genes in the exposed NHBE cells as compared to unexposed cells suggesting an innate IFN I mediated immune response in NHBE [7]. We hypothesized that IFN I could also have a central role in mediation of innate immune response in NHBE cells following exposure to indoor PM10. Literature review revealed no previous study on the role of the IFN I pathway in bronchial epithelial responses to respirable PM10 exposure. In this study, we explored the role of IFN 1 in NHBE cells following exposure to PM10 dust in a highly polluted urban setting.

Materials and Methods
Indoor PM10 was collected from a residential setting (patient houses) in Delhi, India on 37mm This study found a statistically significant increase in multiple cytokines in a lung-on-chip model after exposure to indoor particles composed of various chemical elements (most commonly silicon).
Specifically, INF- concentrations increased relative to non-exposed lung models (p <0.02) along with an associated increase in other cytokines (IFN, IL-6, TNF- , and GM-CSF) suggesting a complex immune response involving the interplay between multiple related cytokines.
IFN is produced by almost all body cells including epithelial cells. IFN is known as a moving target due its ability to mediate opposing effects [10]. While IFN demonstrates an anti-inflammatory role in virally infected epithelium and multiple sclerosis, it is also the potential orchestrator of pathological inflammation in certain immune disorders such as systemic lupus erythematosus [6]. Its dichotomous role in inflammation is explained by its opposing effects on helper T cell subtypes, TH1 and TH2. Previous studies show IFN can enhance TH1 response via activation of inflammatory cytokines including IL12, IL18 and caspase1 and inhibit TH2 via activation of IL4 [11,12].
TH1 mediated response is further reinforced by TH1 secreted IFN which increases naïve T-cell responsiveness to IL12 [12]. Our study revealed elevated levels of IFN (p< 0.001), suggesting a complementary role of IFN in propagation of TH1 response.
There is evidence suggesting that IFN mediates an increases in IL6, a cytokine which was elevated in our study (p<0.01), in the setting of toll-like receptor (TLR) 8 activation in neutrophils [13].
TLR8 is an endosomal receptor known to recognize single-stranded DNA viral proteins [13]. Given that TLR8 are also present in bronchial epithelial cells suggests a possible mechanism of IL6 activation via IFN. Furthermore, the process of IL6 activation is potentiated by the TH1 committed proinflammatory cytokine tumor necrotizing factor (TNF), which was also elevated in our study (p<0.01) [13].
Our proposed mechanism for the sequence of cytokine release is listed as the following. Indoor aerosolized particle matter first deposits in bronchial airways. IFN is produced by bronchial epithelial cells which leads to TH1 activation and TH2 inhibition. Activation of TH1 cells leads to the subsequent release of cytokines IFN and TNF. IFN further increases naive TH1 cell activation and mediates increases in IL6 via action of TLR 8 found in bronchial epithelial cells. Similarly, TNF potentiates IL6 signaling.
The mechanism of PM10 induced inflammation is largely still unknown, but the inflammatory host response to aerosolized particulate matter has been previously studied. Bossmann et al. studied the inflammatory response in peripheral blood mononuclear cells after exposure to PM10 particles and found notable increases in TNF α, IL-6, and IL-1β [14]. Park et al. studied human dermal fibroblast response to PM10 and observed increases in IL-1β, IL-6, IL-8 and IL33 [15]. Becker et al. found that alveolar macrophage response to virally infected lung epithelial cells was altered in response to PM10 exposure [16]. Ramage et al. found increased expression of C-reactive protein and heat-shock protein-