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Interactions between Innate Antiviral and Atopic Immunoinflammatory Pathways Precipitate and Sustain Asthma Exacerbations in Children¹

Telethon Institute for Child Health Research, and Centre for Child Health Research, Faculty of Medicine and Dentistry, The University of Western Australia, Perth, Western Australia, Australia

Severe asthma exacerbations in children requiring hospitalization are typically associated with viral infection and occur almost exclusively among atopics, but the significance of these comorbidities is unknown. We hypothesized that underlying interactions between immunoinflammatory pathways related to responses to aeroallergen and virus are involved, and that evidence of these interactions is detectable in circulating cells during exacerbations. To address this hypothesis we used a genomics-based approach involving profiling of PBMC subpopulations collected during exacerbation vs convalescence by microarray and flow cytometry. We demonstrate that circulating T cells manifest the postactivated "exhausted" phenotype during exacerbations, whereas monocyte/dendritic cell populations display up-regulated CCR2 expression accompanied by phenotypic changes that have strong potential for enhancing local inflammation after their recruitment to the atopic lung. Notably, up-regulation of FcR1, which is known to markedly amplify capacity for allergen uptake/presentation to Th2 effector cells via IgE-mediated allergen capture, and secondarily programming of IL-4/IL-13-dependent IL-13R⁺ alternatively activated macrophages that have been demonstrated in experimental settings to be a potent source of autocrine IL-13 production. We additionally show that this disease-associated activation profile can be reproduced in vitro by cytokine exposure of atopic monocytes, and furthermore that IFN- can exert both positive and negative roles in the process. Our findings suggest that respiratory viral infection in atopic children may initiate an atopy-dependent cascade that amplifies and sustains airway inflammation initiated by innate antiviral immunity via harnessing underlying atopy-associated mechanisms. These interactions may account for the unique susceptibility of atopics to severe viral-induced asthma exacerbations.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was funded by National Health and Medical Research Council of Australia. I.A.L. is supported by The Australian Respiratory Council Ann Woolcock Research Fellowship.

² Address correspondence and reprint requests to Dr. Patrick G. Holt, Division of Cell Biology, Telethon Institute for Child Health Research, PO Box 855, West Perth, Western Australia 6872, Australia. E-mail addresses: patrick{at}ichr.uwa.edu.au and kathym{at}ichr.uwa.edu.au

³ Abbreviations used in this paper: DC, dendritic cell; AAC, activated macrophage/monocyte; mDC, myeloid DC; pDC, plasmacytoid DC; qRT-PCR, quantitative RT-PCR.

⁴ The online version of this article contains supplemental material.