Comparative analysis of the tear protein profile in mycotic keratitis patients

PURPOSE Mycotic keratitis is a major cause of corneal blindness in India. A proper understanding of the pathogenesis may help in refining the existing treatment. The purpose of this study is to examine the total tear protein profile of fungal keratitis patients, which may have a bearing on pathogenesis and disease progression. METHODS Tear samples were collected from culture positive fungal keratitis patients. Tears from the uninfected fellow eye and from other healthy individuals served as controls. Two-dimensional electrophoresis (2DE) was used for the separation of fractionated tear proteins, and selected protein spots, which showed differential expressions, were identified using matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry. Wherever needed, tag sequencing of peptide fragments using post source decay (PSD) was done to confirm the identification. RESULTS The glutaredoxin-related protein was expressed only in the tears of fungal keratitis patients. Six other normal tear proteins were present in both samples but with varied expression levels. Prolactin inducible protein and serum albumin precursor were upregulated in the infected samples. Cystatin S precursor, cystatin SN precursor, cystatin, and human tear lipocalin were downregulated in the infected samples. CONCLUSIONS Tears can be used as a clinical source to study the proteomic responses in patients with fungal keratitis. The glutaredoxin-related protein is known to be produced by Aspergillus during oxidative stress conditions, and the presence of this protein in the tears of patients with mycotic keratitis indicates that this pathogen undergoes stress-related gene expression during infection.