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A1338 - Activin-A Regulates Expression of TLR3 and TLR4 by Asthmatic Bronchial Epithelial Cells in an Autocrine Fashion
Author Block: M. White1, K. A. Barrow2, S. R. Reeves3, R. James1, J. S. Debley4; 1Seattle Children's Research Institute, Seattle, WA, United States, 2Seattle Children's Research Institute, seattle, WA, United States, 3Pediatric Pulmonology, Seattle Children's Hosp, Seattle, WA, United States, 4Pulmonary and Sleep Medicine, Seattle Children's Hospital, Seattle, WA, United States.
Rationale: Elevated activin-A levels in bronchoalveolar lavage fluid and serum, and increased activin-A immunostaining in bronchial epithelial cells, have been observed in asthmatic subjects. In vivo and in vitro data suggest that activin-A, a TGFβ superfamily member, may play an important role in the regulation of airway inflammation in asthma. However, there is conflicting published data regarding whether this cytokine has predominantly pro- or anti-inflammatory effects in asthma, or whether its actions have differing directionality within different cell and tissue types or milieus. Aim: Determine if knockdown of activin A in differentiated bronchial epithelial cells (BECs) from asthmatic children influences the expression of epithelial immunomodulatory or innate immune response factors. Methods: BECs from asthmatic children (n=12) were transduced in submerged conditions with a doxycycline(dox)-inducible lentiviral shRNA system carrying shRNA against activin A, differentiated at an air-liquid interface for 21 days, then exposed to doxycycline for 48hrs to knockdown (KD) activin A. Expression of TSLP, IL-33, IFN-β1, IFIH1, IRF7, toll-like receptor 3 (TLR3), and toll-like receptor 4 (TLR4) was measured by qPCR in BECs following activin A KD by doxycycline exposure, and compared to expression by BECs not exposed to doxycycline. Results: Exposure of BECs transduced by a (dox)-inducible lentiviral vector carrying shRNA against activin A to doxycycline reduced the concentration of activin A in supernatant by approximately 50% compared to transduced BECs not exposed to doxycycline. Expression of TSLP, IL-33, IFN-β1, IFIH1, and IRF7 by BECs did not significantly change following activin A KD. However, BEC expression of TLR3 was 25% greater (p=0.001) and TLR4 was 40% greater (p=0.02) following activin A KD as compared to BECs wherein activin A was not knocked down. Among BECs from donors with a history of severe asthma exacerbation (n=9) TLR3 expression was 75% greater (p=0.008) and TLR4 was 70% greater (p=0.004) following activin A KD. Conclusion: TLR3 and TLR4 play fundamental roles in pathogen recognition and activation of innate immune responses to viral (TLR3) and bacterial (TLR4) pathogens. Activin A appears to negatively regulate expression of TLR3 and TLR4 by airway epithelial cells from children with asthma, especially among children with a history of severe exacerbations. Further investigation of the role of activin A in regulating innate immune responses by the airway epithelium in asthma, and in modifying the risk of viral-triggered exacerbation, is warranted.