Toll-like receptors involved in the pathogenesis of experimental Candida albicans keratitis

Abstract

PURPOSE. To investigate the expression and function of toll-like receptors (TLRs) during experimental keratomycosis. METHODS. Scarified corneas of BALB/c mice were topically inoculated with Candida albicans and compared with control corneas by a murine gene microarray and immunostaining. Real-time reverse transcription polymerase chain reaction (RTPCR) determined relative TLR gene expression in murine and human donor corneas. The scarified corneas of TLR2-/- mice, TLR4-/- mice, and C57BL/6J control mice were also inoculated with C. albicans, to determine relative severity, fungal load, and cytokine transcript levels. RESULTS. TLR1,-2,-4,-6, and-13 were significantly upregulated (5-to 10-fold; P < 0.01) by microarray, and TLR1,-2,-4, and-13 were significantly increased (4-to 11-fold; P < 0.05) by realtime RT-PCR in BALB/c murine corneas. Similarly, TLR2,-6, and-13 were significantly upregulated (5-to 16-fold; P ≤ 0.001) by real-time RT-PCR in C57BL/6J murine corneas the day after inoculation, and TLR2 and-13 remained significantly (P < 0.05) increased after 1 week. TLR2 transcript was also upregulated twofold (P < 0.04) in C. albicans-inoculated explanted human corneas. Although murine keratitis severity scores were similar, significantly more fungi were recovered from TLR2-/- mouse corneas (P < 0.04) than from TLR4-/- mouse corneas (P = 0.9). Tumor necrosis factor-α, interleukin 23, chemokine C-C ligands 3 and 4, and dectin-1 were significantly (P < 0.05) downregulated in C. albicans-infected corneas of TLR2-/- mice. CONCLUSIONS. TLR2 signals proinflammatory cytokines that control fungal growth during C. albicans keratitis. TLR13 may have an additional role in the innate immune response of murine corneal candidiasis. © Association for Research in Vision and Ophthalmology.