The epithelium is an essential tissue that lines the surfaces of organs and blood vessels. Being a first-line defense, epithelium defenses against the antigens mainly by an orchestrated immunological process involving the junctions, innate immune response, and adaptive immune response. The cell-cell interactions at the juncture between adjacent epithelial cells, including the tight junctions, the desmosomes, and adherence junctions, form the physical foundation of the barrier function; the cellular response to a variety of pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs) also regulates the intrinsic barrier function. Specific epithelial cells secrete high molecular weight glycoproteins, pattern recognition receptors, and multiple antimicrobial peptides to form the extrinsic barrier.

Being an unique and important sensory organ, the eye has a precise regulatory mechanism for each component to accomplish its function. The epithelium in the eye each evolved a unique structure and function. For example, the corneal and conjunctival epithelium developed mechanisms to keep moisturized and defend against pathogens or allergens from the open air; while retina pigment epithelium forms the outer blood-retinal barrier and nourishes the photoreceptors. A better understanding of these epithelium and epithelial cells in the eye is essential for vision protection. This collection aims to demonstrate standardized protocols for epithelium research of the eye, lower the threshold for researchers interested in the field, and ultimately promote research against blindness.