Allergenic proteases cleave the chemokine CX3CL1 directly from the surface of airway epithelium and augment the effect of Rhinovirus

Abstract

CX3CL1 has been implicated in allergen-induced airway CD4+ T lymphocyte recruitment in asthma. Since epidemiological evidence supports a viral infection-allergen synergy in asthma exacerbations, we postulated that rhinovirus (RV) infection in the presence of allergen augments epithelial CX3CL1 release. Fully differentiated primary bronchial epithelial cultures were pre-treated apically with house dust mite extract (HDM) and infected with RV16. CX3CL1 was measured by ELISA and western blotting, and shedding mechanisms assessed using inhibitors, PAR2 agonist, and recombinant CX3CL1-expressing HEK293 cells. Basolateral CX3CL1 release was unaffected by HDM but stimulated by RV16; inhibition by fluticasone or GM6001 implicated NF-κB and ADAM sheddases. Conversely, apical CX3CL1 shedding was stimulated by HDM, augmented by RV16. Although fluticasone or GM6001 reduced RV16+HDM-induced apical CX3CL1 release, heat-inactivation or cysteine protease inhibition completely blocked CX3CL1 shedding. HDM effect was via enzymatic cleavage of CX3CL1, not PAR2 activation, yielding a product mitogenic for smooth muscle cells. Extracts of Alternaria fungus caused similar CX3CL1 shedding. We have identified a novel mechanism whereby allergenic proteases cleave CX3CL1 from the apical epithelial surface to yield an active product. RV16 infection augmented HDM-induced CX3CL1 shedding – this may contribute to synergy between allergen exposure and RV infection in triggering asthma exacerbations and airway remodelling.

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Identifiers

ORCID for Matthew Loxham: orcid.org/0000-0001-6459-538X

ORCID for Cornelia Blume: orcid.org/0000-0001-6133-7318

ORCID for Emily Swindle: orcid.org/0000-0003-3644-7747

ORCID for Donna Davies: orcid.org/0000-0002-5117-2991

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