TLR4 Contributes to the Host Response toKlebsiellaIntraocular Infection

Abstract

Purpose/Aim Klebsiella pneumoniae causes a blinding infection called endogenous endophthalmitis. The role of innate immune recognition of K. pneumoniae in the eye during infection is not known. We hypothesized that intraocular recognition of K. pneumoniae was mediated by TLR4 and may be dependent on MagA-regulated hypermucoviscosity. Materials and Methods Experimental endophthalmitis was induced in C57BL/6J or TLR4−/− mice by intravitreal injection of 100 CFU of wild type or ΔmagA K. pneumoniae. Infection and inflammation were quantified by determining viable K. pneumoniae per eye, retinal responses via electroretinography, myeloperoxidase activity of infiltrating neutrophils, and the proinflammatory cytokine and chemokine response. Results C57BL/6J and TLR4−/− mice could not control intraocular wild type K. pneumoniae growth. TLR4−/− mice were less able than C57BL/6J to control the intraocular growth of ΔmagA K. pneumoniae. Retinal function testing suggested that infection with ΔmagA K. pneumoniae resulted in less retinal function loss. There was a TLR4-dependent delay in initial neutrophil recruitment, regardless of the infecting organism. The proinflammatory cytokine/chemokine data supported these results. These findings were not due to an inability of TLR4−/− neutrophils to recognize or kill K. pneumoniae. Conclusions These studies suggest that TLR4 is important in the early intraocular recognition and host response to K. pneumoniae. However, the role of MagA in TLR4-mediated intraocular recognition and subsequent inflammation is less clear.

Unexpected Roles for Toll-Like Receptor 4 and TRIF in Intraocular Infection with Gram-Positive Bacteria

“…We recently reported that the absence of TLR4 resulted in a delayed inflammatory response in experimental Klebsiella pneumoniae endophthalmitis (38). Tullos et al also proposed that TLR2 and TLR4 modulated the immune response in a Streptococcus pneumoniae keratitis model, with TLR2 aiding in bacterial clearance and the absence of TLR4 contributing to reduced disease pathogenesis (53).…”

“…Analysis of phagocytosis and killing activity was performed with freshly isolated neutrophils from C57BL/6J and TLR4 Ϫ/Ϫ mice (37,38). B. cereus strain ATCC 14579 and neutrophils were incubated separately in PBS containing 10% heat-inactivated C57BL/6J mouse serum at 37°C (Valley Biomedical Products, Winchester, VA).…”

Zebrafish are Resistant to Staphylococcus aureus Endophthalmitis

“…In clinical settings, most bacterial endophthalmitis arises due to postsurgical complications (e.g., cataract surgery), where pathogens from the ocular surface gain access to the eye and cause ocular tissue damage [28,29]. To mimic this situation, studies from our [7,26,30] and other laboratories [31,32] have developed murine models where bacteria are directly inoculated in the vitreous cavity. Previous studies have demonstrated that S. aureus caused endophthalmitis in mice when eyes were inoculated with 5000 or less CFUs [7,10,33,34].…”

Modeling intraocular bacterial infections

“…Surprisingly, deficiencies in Toll/IL-1 receptor domain-containing adapter-inducing interferon β (TRIF, the intracellular adaptor molecule for TLR4) and in TLR4 itself also resulted in significantly less intraocular inflammation during experimental B. cereus endophthalmitis, suggesting that MyD88-independent pathways were involved in the intraocular response to B. cereus and that B. cereus may harbor ligands for TLR4 which instigate intraocular inflammation (Parkunan et al, 2015). The importance of TLR4 in experimental K. pneumoniae endophthalmitis was demonstrated using TLR4-deficient mice (Hunt et al, 2014). The data on the course of infection in the K. pneumoniae endophthalmitis mouse model (Wiskur et al, 2008a) were cited by Ishii et al as providing guidance in the successful treatment of a patient with K. pneumoniae endophthalmitis (Ishii et al, 2011), emphasizing the clinical value of these experimental models.…”

“…Polymorphonuclear neutrophils (PMN) have been identified as the earliest cell type to invade the posterior segment and retina during endophthalmitis caused by a number of species (Booth et al, 1995; Hunt et al, 2014; Jett et al, 1992; Ramadan et al, 2006; Sanders et al, 2010; Talreja et al, 2014). PMN infiltration coincided with permeability of the blood-ocular barrier which, in mice, occurred as early as four hours post- Bacillus infection (Moyer et al, 2009).…”