Toll-Like Receptor 2 Regulates Organic Dust–Induced Airway Inflammation

Abstract

Organic dust exposure in agricultural environments results in significant airway inflammatory diseases. Gram-positive cell wall components are present in high concentrations in animal farming dusts, but their role in mediating dust-induced airway inflammation is not clear. This study investigated the role of Toll-like receptor (TLR) 2, a pattern recognition receptor for gram-positive cell wall products, in regulating swine facility organic dust extract (DE)-induced airway inflammation in mice. Isolated lung macrophages from TLR2 knockout mice demonstrated reduced TNF-α, IL-6, keratinocyte chemoattractant/CXCL1, but not macrophage inflammatory protein-2/CXCL2 expression, after DE stimulation ex vivo. Next, using an established mouse model of intranasal inhalation challenge, we analyzed bronchoalveolar lavage fluid and lung tissue in TLR2-deficient and wild-type (WT) mice after single and repetitive DE challenge. Neutrophil influx and select cytokines/chemokines were significantly lower in TLR2-deficient mice at 5 and 24 hours after single DE challenge. After daily exposure to DE for 2 weeks, there were significant reductions in total cellularity, neutrophil influx, and TNF-α, IL-6, CXCL1, but not CXCL2 expression, in TLR2-deficient mice as compared with WT animals. Lung pathology revealed that bronchiolar inflammation, but not alveolar inflammation, was reduced in TLR2-deficient mice after repetitive exposure. Airway hyperresponsiveness to methacholine after dust exposure was similar in both groups. Finally, airway inflammatory responses in WT mice after challenge with a TLR2 agonist, peptidoglycan, resembled DE-induced responses. Collectively, these results demonstrate that the TLR2 pathway is important in regulating swine facility organic dust-induced airway inflammation, which suggests the importance of TLR2 agonists in mediating large animal farming-induced airway inflammatory responses.

Extracellular Vesicles Derived from Gram-Negative Bacteria, such asEscherichia coli, Induce Emphysema Mainly via IL-17A–Mediated Neutrophilic Inflammation

“…Common biological contaminants in indoor dust include viruses, bacteria, fungi, dust mites, and pet dander (21,22). Previous reports indicate that organic dust can induce airway inflammation related with Th1/Th17 cell responses or TLR2 signaling (23,24). Our previous findings showed that indoor dust collected from bed mattress induces neutrophilic pulmonary inflammation and that EVs in indoor dust also induce neutrophilic pulmonary inflammation, which is related with Th1 and Th17 cell responses (25).…”

Toll-like Receptor 4 Signaling Pathway Mediates Inhalant Organic Dust-Induced Bone Loss

“…Utilizing culture-dependent and culture-independent techniques, several studies have demonstrated a high burden of gram positive bacteria rather than gram negative bacteria, in organic dust samples from swine confinement buildings [18,20,41]. Previously, we demonstrated that exposure to gram positive peptidoglycan elicited airway inflammatory consequences in rodents similar to that observed with swine facility organic dust extracts, and that TLR4 in Inhalant Bioaerosol-Induced Bone Loss TLR2 signaling pathway was important in mediating airway inflammatory disease [22]. Importantly, TLR2 but not TLR4 gene polymorphisms were demonstrated by others to be associated with lung function among swine workers [21].…”

“…inhalation exposure animal model was utilized whereby mice were lightly sedated under isoflurane and received treatment with 50 μl of sterile saline (PBS) or 12.5% ODE (50 μl volume) daily for 3 weeks [22,30,34]. Animals were euthanized and measurements taken 5 hours following the final inhalation treatment.…”

“…Recent studies have described a predominance of gram positive bacteria in agriculture dust samples [18][19][20], and genetic polymorphisms in Toll-like receptor 2 (TLR2) gene have been associated with airway disease in swine confinement workers [21]. In animal studies, TLR2, which recognizes peptidoglycans, lipoteichoic acid and lipopoproteins associated with gram positive bacteria, and TLR4, which recognizes gram negative endotoxin, have been both implicated in regulating organic dust-induced lung inflammation [22][23][24]. Specifically, in mice deficient in TLR2 or TLR4 and challenged with organic dust environments or extracts, it has been demonstrated there is up to a 50% reduction in various airway inflammatory consequences [22,24].…”

“…In animal studies, TLR2, which recognizes peptidoglycans, lipoteichoic acid and lipopoproteins associated with gram positive bacteria, and TLR4, which recognizes gram negative endotoxin, have been both implicated in regulating organic dust-induced lung inflammation [22][23][24]. Specifically, in mice deficient in TLR2 or TLR4 and challenged with organic dust environments or extracts, it has been demonstrated there is up to a 50% reduction in various airway inflammatory consequences [22,24]. However, their respective role in mediating systemic bone consequences has not been previously described.…”