Inflammasome activation in airway macrophages and the lung microbiome in IPF

Abstract

Airway Macrophages (AMs) are important in the pathogenesis of lung fibrosis. Inflammasomes (NLRP3,AIM2,NLRC4) are cytosolic receptors of the innate immune system responsible for cleavage of IL-1b, a proinflammatory,profibrotic cytokine. Inflammasomes respond to local microbiota changes. In IPF the bacterial burden is elevated and its composition is altered. AIM2 is increased and linked to exacerbation of fibrosis after Streptococcal infection (Cho,Thorax 2019). In IPF exacerbations, top upregulated genes in the BAL are IL-1b and NLRP3. MtROS drives NLRP3 activation and is elevated in IPF AMs (Tsitoura,RespRes 2019). We hypothesised that changes in lung microbiota in IPF may drive Inflammasome activation. As such, we studied the capacity of AMs to activate inflammasomes in relation to microbial burden and mtROS. We prospectively enrolled healthy and IPF subjects and isolated AMs from BAL. AMs were treated with specific inflammasome stimuli; ATP for NLRP3, dsDNA for AIM2, flagellin for NLRC4. IL-1b release was measured by ELISA, BAL microbial burden by 16S rRNA qPCR and mtROS by flow cytometry. The samples are sent for lung microbiome characterisation. Upon stimulation, IPF AMs over activate NLPR3 and AIM2 but not NLRC4. Baseline IL-1b release was similar between groups. Excessive inflammasome activation was linked to higher baseline mtROS. Microbial burden tended to be increased in IPF. Microbial burden correlated with baseline IL1b release. There was a strong association between the levels of 16S rRNA and relative AIM2 mRNA. Our results reveal a possible novel role of inflammasomes’ response to local microbiota changes which could be associated with the pathogenesis of IPF acute exacerbations.