Mast cell activation protects cornea by promoting neutrophil infiltration via stimulating ICAM-1 and limbal vascular dilation and permeability in fungal keratitis

Abstract

Purpose : The role of mast cells (MCs) in fungal infection is largely unknown. This study was to explore a protective role and mechanism of MCs in fungal keratitis.

Methods : Experimental fungal keratitis (FK) was developed in C57BL/6J mice infected with Fusarium solani after corneal wound. Mice untreated (UT) or receiving corneal wound without fungal infection (Mock) were used as controls. The clinical manifestation, corneal infection score and perforation rate were evaluated by a slit lamp microscope. Cromolyn sodium was used to block mast cell activation. Corneal whole mount immunofluorescence was performed to observe vascular diameter, MC activation and neutrophil chemotaxis. Evans blue was used to detect vascular permeability. Intercellular adhesion factor -1 (ICAM-1) was measured by ELISA. GMS or HE staining was used to evaluate tissue damage and infiltration of fungal hyphae and inflammatory cells by a corneal confocal microscopy.

Results : Large number of MCs was found to locate at corneal limbus and conjunctiva around blood vessels and nerves in normal and treated mice. MC activation with degranulation was largely observed in FK mice after corneal infection for 6-72 hours, and the percentages of degranulated/total cells was significant higher in FK than Mock and UT mice. Dialated limbal vasculature with increased permeability, as well as largely infiltrated neutrophils with stimulated ICAM-1 protein levels were observed in corneas of FK mice, when compared with Mock and UT mice. Interestingly, pretreatment with cromolyn sodium (Block) significantly blocked MC degranulation, dramatically suppressed vascular dilation and permeability, and markedly reduced neutrophil infiltration with lower ICAM-1 levels in the infected cornea of FK mice at 6-24 hours. Furthermore, the Block mice manifested prolonged disease course, increased pathological damage, and vigorous fungi growth, with much higher corneal perforation rate (83.33%, P<0.05) than FK mice (33.33%) at 72h.

Conclusions : This study reveals a novel phenomenon that mast cells play a vital role in protecting cornea against fungal infection through degranulation that promotes neutrophil infiltration via stimulating ICAM-1 production and limbal vascular dilation and permeability.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.