Role of neutrophils, MyD88-mediated neutrophil recruitment, and complement in antibody-mediated defense against Pseudomonas aeruginosa keratitis.

Purpose. Ulcerative keratitis due to Pseudomonas aeruginosa is a sight-threatening disease leading to loss of vision due to corneal inflammation. A human IgG1 monoclonal antibody (MAb F429) to the alginate capsule significantly reduces pathology and bacterial burdens in the cornea when applied topically starting 8 hours post-infection. The purpose of this study was to determine whether local polymorphonuclear neutrophils (PMN) recruitment and complement were important lipopolysaccharide co-factors in MAb F429-mediated reductions in P. aeruginosa tissue levels and corneal pathology. Methods. MyD88 knock-out mice unable to recruit PMN to tissues, mice depleted of PMNs, or mice depleted of complement component C3 were topically treated with MAb F429 starting 8 hours post-infection and evaluated for bacterial levels and corneal pathology 48 hours after infection with two P. aeruginosa isolates. Results. An inability to recruit PMN or systemic PMN depletion plus topical application of MAb F429 resulted in less pathology in the eye, but bacterial burdens were markedly increased in the cornea, brains, and spleens of these mice, indicative of systemic spread. Intraperitoneal injection of cobra venom factor (CVF) reduced C3 levels in the cornea approximately 40%, which did not change the beneficial effects of MAb F429. Both systemic injection and topical application of CVF reduced local C3 levels >60%, which eliminated MAb-mediated reductions in corneal pathology and bacterial levels. Conclusions. PMN recruitment and complement are both needed for maximal in vivo efficacy of MAb F429 in therapeutically treating P. aeruginosa keratitis, and attempts to reduce pathology by limiting PMN influx could have consequences leading to more extensive local and systemic infection.