Karthikeyan et al. examined corneal ulcers from patients with P. aeruginosa and found elevated expression of the pathogen recognition receptors TLR2, TLR4 and TLR9, pro-inflammatory cytokines IL-1α, IL-1β, and IFN-γ, and the inflammasome components NLRP3, NLRC4 and ASC compared with donor corneas [44]. Here, TLR4 is linked to corneal infection.