Activation of Conjunctiva-Associated Lymphoid Tissue in Patients With Infectious Keratitis Using In Vivo Confocal Microscopy

PURPOSE: We aimed to evaluate activation of conjunctiva-associated lymphoid tissue (CALT) in patients with keratitis using in vivo confocal microscopy (IVCM) and conjunctival impression cytology (CIC). METHODS: In addition to anterior segment photography and corneal fluorescein staining, IVCM revealed the palpebral conjunctiva in all subjects, and CIC and immunofluorescence staining were performed. RESULTS: Diffuse lymphoid tissue cell density in the eyes of patients with keratitis was significantly greater compared with healthy volunteers (P < 0.001). Similar trends were found in perifollicular lymphocyte density (P < 0.001), follicular density (P = 0.029), follicular center reflection intensity (P = 0.011), and follicular area (P < 0.001). Immunofluorescence staining showed that the proportions of CD4(+) (61.7% ± 8.0% vs. 17.3% ± 10.2%, respectively, P < 0.001) and CD8(+) (46.9% ± 10.0% vs. 19.6% ± 11.5%, respectively, P < 0.001) cells in patients with keratitis was greater compared with healthy volunteers. Interestingly, we also observed changes in the contralateral eye in subjects with keratitis. CONCLUSIONS: Our research suggests that CALT, as an ocular immune structure, is activated and plays an important role in the pathogenesis of keratitis. This has been overlooked previously. CALT is also active in the contralateral eye of subjects with keratitis.