TLR4 and corneal ulcer: As for the host response in corneal ulcers from patients with culture positive S. pneumoniae, similar to P. aeruginosa, Karthikeyan et al. also found elevated expression of TLR2, TLR4, TLR9, IL-1α, IL-1β, IFN-γ, NLRP3, NLRC4 and ASC compared with control non-infected corneas.