Vitreoretinal Myeloid Cell Heterogeneity: Diverse Roles in Homeostasis, Immune Surveillance, and Pathophysiology.

The retina is a central nervous system tissue with immune-privileged status, protected by the blood-retina barrier and maintained by specialized resident tissue macrophages: microglia, hyalocytes, and perivascular macrophages. These cells exhibit specific ontogeny, spatial localization, and immunologic functions. Each population contributes to homeostasis, phagocytosis, and immunoregulation in their local microenvironment. Microglia are the most abundant immune cells in the retina, and their key functions include vascular and synaptic regulation. Hyalocytes are abundant in the vitreous and at the vitreoretinal interface with key functions including vasoregression and maintenance of a clear visual axis. Perivascular macrophages are present along major venules in the superficial retina and may regulate immune cell transendothelial migration. This review summarizes key vitreoretinal myeloid cell functions, compares/contrasts the relative abundances of antigen presentation machinery and T cell costimulatory molecules, and places these expression levels into the context of immune surveillance in the experimental autoimmune uveitis model.