Expression of macrophage migration inhibitory factor during Pseudomonas keratitis

Macrophage migration inhibitory factor (MIF) is a recently rediscovered pro -inflammatory cytokine, and has been shown to play a role in the regulation of neutrophil chemokines and angiogenesis. Corneal epithelial and endothel ial cells have been shown to express MIF. This study evaluated the expressi on of MIF during Pseudomonas keratitis in mice and in vitro using a corneal epithelial cell line. Three strains of P. aeruginosa, 6294 (invasive strai n), 6206 (cytotoxic strain) and Paer1 (non- infectious strain) were used. B oth cytotoxic and invasive strains were isolated from human corneal ulcers and the Paer1 strain was isolated from a non-infectious condition. Followin g challenge in mouse corneas or a corneal epithelial cell line, corneal hom ogenates or lysed corneal epithelial cells were used to isolate RNA. Migrat ion inhibitory factor mRNA expression in the mouse cornea or human corneal epithelial cells was examined by reverse transcription-polymerase chain rea ction analysis, and was found to be expressed as early as 4 h after the inj ury (scratch controls) or infection in the mouse corneas. Migration inhibit ory factor mRNA in scratch controls and Paer1-inoculated corneas showed pea k levels at 4 h post-challenge and this dropped by 24 h post-challenge. Cor neas challenged with invasive and cytotoxic strains showed peak expression 24 h post-challenge. Migration inhibitory factor mRNA levels were significa ntly higher in invasive and cytotoxic strain inoculated corneas compared to Paer1 inoculated corneas. Challenging the corneal epithelial cell line wit h Pseudomonas 6294 and 6206 strains induced peak expression at 8 h and leve ls were decreased by 12 h. Epithelial cells inoculated with recombinant hum an interleukin-1 beta protein induced very high levels of MIF mRNA at all t ime points compared to infected and control corneal epithelial cells. High expression of MIF in the infected corneas suggests that it may have a role in the pathogenesis of corneal disease induced by invasive and cytotoxic st rains of P. aeruginosa.