TLR 3 Activation Increases Chemokine Expression in 1 Human Fetal Airway Smooth Muscle Cells

47 Viral infections, such as respiratory syncytial virus (RSV) and rhinovirus, adversely affect 48 neonatal and pediatric populations resulting in significant lung morbidity, including acute asthma 49 exacerbation. Studies in adults have demonstrated that human airway smooth muscle (ASM) 50 cells modulate inflammation through their ability to secrete inflammatory cytokines and 51 chemokines. The role of ASM in the developing airway during infection remains undefined. In 52 our study, we used human fetal ASM cells as an in vitro model to examine the effect of toll-like 53 receptor (TLR) agonists on chemokine secretion. We found that fetal ASM express multiple 54 TLRs, including TLR3 and TLR4, which are implicated in the pathogenesis of RSV and 55 rhinovirus infection. Cells were treated with TLR agonists, Poly (I:C) (TLR3 agonist) 56 lipopolysaccharide (LPS; TLR4 agonist), or R848 (TLR7/8 agonist), and IL-8 and CCL5 57 secretion was evaluated. Interestingly, Poly (I:C) but neither LPS nor R848, increased IL-8 and 58 CCL5 secretion. Examination of signaling pathways suggested that the Poly (I:C) effects in fetal 59 ASM involve TLR and ERK signaling, in addition to another major inflammatory pathway, NFκB. 60 Moreover, there are variations between fetal and adult ASM with respect to Poly (I:C) effects on 61 signaling pathways. Pharmacological inhibition suggested that ERK pathways mediate Poly 62 (I:C) effects. Overall, our data show that Poly (I:C) initiates activation of pro-inflammatory 63 pathways in developing ASM, which may contribute to immune responses to infection and 64 exacerbation of asthma. 65