Features of the Immunologic Microenvironment
The cornea is unique in that the peripheral and central portions of the tissue represent distinctly different immunologic microenvironments. In normal eyes, only the limbus is vascularized and richly invested with Langerhans cells. The paracentral and central cornea are normally devoid of APCs and are avascular. Various stimuli, such as mild trauma, certain cytokines (eg, interleukin-1), or infection, can recruit APCs to the central cornea. Plasma-derived proteins (eg, complement, IgM, and IgG) are present in moderate concentrations in the periphery, but only low levels of IgM are present centrally.
Corneal cells also appear to synthesize various antimicrobial and immunoregulatory proteins. Effector cells are absent or scarce in the normal cornea, but neutrophils, monocytes, and lymphocytes can readily migrate through the stroma if appropriate chemotactic stimuli are activated. Lymphocytes, monocytes, and neutrophils can also adhere to the endothelial surface during inflammation, giving rise to keratic precipitates or the classic Khodadoust line of endothelial rejection (Fig 3-1). Localized immune processing probably does not occur in the cornea. See also BCSC Section 8, External Disease and Cornea.
Excerpted from BCSC 2020-2021 series: Section 9 - Uveitis and Ocular Inflammation. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.