Microbiome of the Lower Airways Alters Corticosteroid Responsiveness in Asthma

There have been no functional studies defining the effects of airway microbiome on corticosteroid response in asthma. Bacterial 16s rRNA gene sequencing from bronchoalveolar lavage (BAL) samples of 29 corticosteroid resistant (CR), 10 corticosteroid sensitive (CS) asthmatics and 12 healthy controls was performed. Patients were defined as CR if <10% improvement in lung function following one week of oral prednisone treatment occurred. BAL macrophages/peripheral blood monocytes from asthmatics were stimulated with pathogenic vs commensal organisms, treated with 10-6M dexamethasone (DEX) for 3hr and analyzed for the expression of corticosteroid-regulated genes by real-time PCR. Cellular MAPK activation was assessed by Western blot. 34 out of 39 asthmatics had expansions of specific groups of microorganisms (>5% of 16s rRNA sequences, >2 fold above microbes present in healthy controls or unique organisms) and significant reduction of sequences for Genera Prevotella, major airway commensal organism (23.8% vs 53.2% of total 16s rRNA sequences, p=0.001). Six CR, but none of CS, asthmatics had expansions of Neisseria/Haemophilus. Preincubation of monocytes and macrophages from asthmatics with Haemophilus parainfluenzae, representative pathogenic organism from CR asthma airways, but not Prevotella melaninogenica, resulted in MAPK activation, IL-8 upregulation and inhibition of cellular response to corticosteroids (IL-8 fold suppression by DEX 2.5±1.1 vs 14.3±1.3, respectively, p=0.001). Toll-like receptor pathway inhibitors restored cellular sensitivity to corticosteroids. A subgroup of CR asthmatics demonstrates lower airway expansion of Neisseria/Haemophilus, which trigger MAPK activation and inhibit airway macrophages/monocytes response to corticosteroids. Toll-like receptor pathway inhibitors restore cellular sensitivity to corticosteroids in presence of these bacteria.