Abstract
Relevance. Bacterial keratitis is one of the most common infectious diseases of the cornea and may lead to severe complications, persistent visual impairment, and disability.
Aim. To investigate the levels of interleukin-6 and the tight junction protein zonula occludens-1 in the tear fluid of patients with bacterial keratitis according to the presence of type 2 diabetes mellitus and to assess their association with the clinical course and development of disease complications.
Materials and methods. A prospective comparative multicentre cohort study involving 88 participants was conducted, including patients with bacterial keratitis with and without type 2 diabetes mellitus, as well as healthy controls. Concentrations of interleukin-6 and the tight junction protein zonula occludens-1 in tear fluid were determined using enzyme-linked immunosorbent assay (ELISA).
Results. Significantly elevated concentrations of interleukin-6 and zonula occludens-1 were detected in patients with bacterial keratitis compared with the control group. The highest levels of both biomarkers were observed in patients with concomitant type 2 diabetes mellitus. The concentration of interleukin-6 in patients with bacterial keratitis without diabetes mellitus was 245 [170;390] pg/mL, whereas in patients with concomitant type 2 diabetes mellitus it reached 430 [310;610] pg/mL. The level of zonula occludens-1 was 6.8 [4.9;9.5] ng/mL and 9.6 [7.2;13.4] ng/mL, respectively. Statistically significant positive correlations were found between the levels of the investigated biomarkers and the thickness, width, and area of corneal infiltrates. The strongest correlations were observed between interleukin-6 concentration and infiltrate thickness (ρ = 0.74; p < 0.001), as well as between zonula occludens-1 level and infiltrate thickness (ρ = 0.76; p < 0.001) in patients with type 2 diabetes mellitus. Patients with infiltrate ulceration, delayed epithelialisation, and stromal opacity demonstrated significantly higher levels of both biomarkers compared with those without a complicated disease course.
Conclusions. Bacterial keratitis is associated with increased levels of interleukin-6 and the tight junction protein zonula occludens-1 in tear fluid. The investigated biomarkers were associated with morphometric characteristics of corneal infiltrates and the development of clinical complications of the disease.