The presence of microbiota protects against Pseudomonas aeruginosa induced keratitis

Abstract

Abstract The impact of microbiota on ocular immunity is unclear. We report that in health, the presence of microbiota strengthens the ocular innate immune barrier function and promotes resistance to infection. Consistent with this view, Germ-Free mice (GF) on a SW background that are typically resistant to P. aeruginosa-induced keratitis were rendered susceptible by the lack of microbiota. This was exemplified by increased corneal bacterial burden and elevated pathology of the GF when compared to conventionally maintained specific pathogen free SW mice (SPF). The elevated susceptibility correlated with significant decrease in the antimicrobial capacity of neutrophils derived from GF SW against P. aeruginosa (PA). Oral antibiotic treatment of SPF SW reduced the ability of neutrophils to kill PA in vitro and in vivo, demonstrating that microbiota-derived cues maintain neutrophil priming in the bone marrow against PA. In contrast, topical antibiotic treatment reduced ocular commensal presence at the conjunctival surface, but did not the resistance to infection, suggesting that microbiota resident at a site different from the ocular mucosal tissue are responsible for neutrophil priming. Consistent with this reconstitutions of GF with mouse or human-derived gut microbiota restored resistance to infectious ocular challenge. To determine the mechanims of commensal priming, RNAseq experiments comparing the phenotype of GF and SPF-derived neutrophils were carried out and showed alterations in type I interferon-dependent gene expression profiles, implicating IFN-dependent pathways in microbiota-dependent neutrophil maturation. Indeed, type I interferon priming of GF mice reconstituted neutrophil bactericidal activities against PA.