Toll-Like Receptor 3 is Expressed in All Layers of the Human Sensory Retina and Retinal Pigment Epithelium

Purpose: Recent studies have found that dysregulation of Toll-like receptor 3 (TLR3)-a key player in innate immunity-in retinal pigmented epithelium (RPE) may play a role in retinal oxidative stress. The aim of this study was to evaluate the expression of TLR3 in all layers of the normal human retina. Methods: Formalin-fixed, paraffin-embedded sections of human donor eyes-with no fundoscopic or microscopic evidence of disease-were used in this study. Mean age of donors was 62.8 ± 31.5 years (12 female, 7 male). Immunohistochemistry was performed using an antibody to human TLR3 and staining was scored according to intensity (0=negative, 1=low-to-moderate, 2=strong) and extent (0=negative, 1=staining ≤50% of cells, 2=staining >50% of cells) of staining. We compared the IRS between the layers in macular and peripheral retina. Results: TLR3 was found to be expressed in all layers of the retina, with differences seen within layers and between cases. The following layers were graded as having a strong IRS: Ganglion Cell, Outer Plexiform, Photoreceptors and RPE. The remaining layers were all graded as weak staining. No significant differences were seen between macular and peripheral retina for TLR3 staining in any retinal layer. Conclusion: Our results demonstrate that TLR3 can be found in all retinal layers. This study provides an overview of TLR3 expression throughout the human retina and thus can serve as a foundation for further research that evaluates aberrant TLR3 function or expression in an array of ophthalmic conditions, including those in which oxidative stress is a factor.