Distinct roles for Dectin-1 and TLR4 in the pathogenesis of Aspergillus fumigatus keratitis

Aspergillus species are a major worldwide cause of corneal ulcers,resulting in visual impairment and blindness in immunocompetent individuals. to enhance our understanding of the pathogenesis of aspergillus keratitis,we developed a murine model in which red fluorescent protein (rfp)-expressing a. fumigatus (af293.1rfp) conidia are injected into the corneal stroma,and disease progression and fungal survival are tracked over time. using mafia mice in which c-fms expressing macrophages and dendritic cells can be induced to undergo apoptosis,we demonstrated that the presence of resident corneal macrophages is essential for production of il-1β and cxcl1/kc,and for recruitment of neutrophils and mononuclear cells into the corneal stroma. we found that β-glucan was highly expressed on germinating conidia and hyphae in the cornea stroma,and that both dectin-1 and phospho-syk were up-regulated in infected corneas. additionally,we show that infected dectin-1-/- corneas have impaired il-1β and cxcl1/kc production,resulting in diminished cellular infiltration and fungal clearance compared with control mice,especially during infection with clinical isolates expressing high β-glucan. in contrast to dectin-1-/- mice,cellular infiltration into infected tlr2-/-,tlr4-/-,and md-2-/- mice corneas was unimpaired,indicating no role for these receptors in cell recruitment; however,fungal killing was significantly reduced in tlr4-/- mice,but not tlr2-/- or md-2-/- mice. we also found that trif-/- and tirap-/- mice exhibited no fungal-killing defects,but that myd88-/- and il-1r1-/- mice were unable to regulate fungal growth. in conclusion,these data are consistent with a model in which β-glucan on a.fumigatus germinating conidia activates dectin-1 on corneal macrophages to produce il-1β,and cxcl1,which together with il-1r1/myd88-dependent activation,results in recruitment of neutrophils to the corneal stroma and tlr4-dependent fungal killing. © 2010 leal jr. et al.