Investigation of the corneal filament in filamentary keratitis.
OBJECTIVE
To date, no studies have elucidated the composition of the corneal filament in detail. In this study, an immunohistochemical technique was used to clarify the exact composition of the corneal filament in filamentary keratitis. In addition, the mechanisms responsible for filament formation were identified.


METHODS
Filaments were obtained from 13 patients with filamentary keratitis with a background of penetrating keratoplasty, aqueous tear deficiency, and severe ocular surface disorders, who were receiving treatment at an outpatient facility. From those tissues, transverse and longitudinal frozen sections were prepared and subjected to an indirect fluorescent immunohistochemical analysis with primary antibodies, including cytokeratins (CK1, -4, -6, -10, -12, and -13), mucins (MUC1, -4, -5AC, and -16), keratinization-related proteins (transglutaminase [TGase]-1 and filaggrin), cell proliferation marker Ki67, and markers of infiltration cells (HLA-DR and neutrophil-elastase). TUNEL staining was used for the detection of apoptosis. Fluorescent images of the sections were inspected with a fluorescence microscope.


RESULTS
The filaments were composed of CK12-positive cells and had a roll-formed central core. They were covered with MUC5AC- and -16-positive mucins including CK4- and -13-positive cells and neutrophil-elastase-positive cells. The filaments also included broken cells and DNA fiber-form postlesional nuclei that were positive for TUNEL staining. However, those areas stained weakly for CK6 and HLA-DR; faintly for CK1, CK10, MUC1, and MUC4; and not at all for Ki67, TGase-1, and filaggrin.


CONCLUSIONS
The results of this research have the potential to open new pathways toward understanding the mechanism that generates the filament in filamentary keratitis, as well as new treatments in the future.
Tanioka
Hidetoshi
H
Department of Ophthalmology, Kyoto Prefectural University of Medicine, Kyoto, Japan. htanioka@koto.kpu-m.ac.jp
Yokoi
Norihiko
N
Komuro
Aoi
A
Shimamoto
Takasumi
T
Kawasaki
Satoshi
S
Matsuda
Akira
A
Kinoshita
Shigeru
S
D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism*; D019573:Epithelium, Corneal / Q000378:metabolism* / Q000473:pathology; D005260:Female; D000091344:Filaggrin Proteins; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D020287:In Situ Nick-End Labeling; D007381:Intermediate Filament Proteins / Q000378:metabolism; D007633:Keratins / Q000378:metabolism; D007634:Keratitis / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D015948:Keratoplasty, Penetrating; D019394:Ki-67 Antigen / Q000378:metabolism; D008297:Male; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D009077:Mucins / Q000378:metabolism; D011503:Transglutaminases / Q000378:metabolism
D015415:Biomarkers; D003598:Cytoskeletal Proteins; C000717249:FLG protein, human; D000091344:Filaggrin Proteins; D007381:Intermediate Filament Proteins; D019394:Ki-67 Antigen; D009077:Mucins; D007633:Keratins; D011503:Transglutaminases; C105804:transglutaminase 1