Afghanistan Particulate Matter Enhances Pro-Inflammatory Responses in IL-13-Exposed Human Airway Epithelium via TLR2 Signaling

Since the start of Afghanistan combat operations in 2001, there has been an increase in complaints of respiratory illnesses in deployed soldiers with no previous history of lung disorders. It is postulated that deployment-related respiratory illnesses are the result of inhalation of desert particulate matter (PM) potentially acting in combination with exposure to other pro-inflammatory compounds. Why some, but not all, soldiers develop respiratory diseases remains unclear. Our goal was to investigate if human airway epithelial cells primed with IL-13, a type 2 inflammatory cytokine, demonstrate stronger pro-inflammatory responses to Afghanistan desert PM (APM). Primary human brushed bronchial epithelial cells from non-deployed, healthy subjects were exposed to APM, both with and without IL-13 pretreatment. APM exposure in conjunction with IL-13 resulted in significantly increased expression of IL-8, a pro-inflammatory cytokine involved in neutrophil recruitment and activation. Furthermore, expression of TLR2 mRNA was increased after combined IL-13 and APM exposure. siRNA-mediated TLR2 knockdown dampened IL-8 production after exposure to APM with IL-13. APM with IL-13 treatment increased IRAK-1 (a downstream signaling molecule of TLR2 signaling) activation, while IRAK-1 knockdown effectively eliminated the IL-8 response to APM and IL-13. Our data suggest that APM exposure may promote neutrophilic inflammation in airways with a type 2 cytokine milieu.