Plasmacytoid dendritic cells in the eye

Plasmacytoid dendritic cells (pDCs) are a unique subpopulation of immune cells, distinct from classical dendritic cells. pDCs are generated in the bone marrow and following development, they typically home to secondary lymphoid tissues. While peripheral tissues are generally devoid of pDCs during steady state, few tissues, including the lung, kidney, vagina, and in particular ocular tissues harbor resident pDCs. pDCs were originally appreciated for their potential to produce large quantities of type I interferons in viral immunity. Subsequent studies have now unraveled their pivotal role in mediating immune responses, in particular in the induction of tolerance. In this review, we summarize our current knowledge on pDCs in ocular tissues in both mice and humans, in particular in the cornea, limbus, conjunctiva, choroid, retina, and lacrimal gland. Further, we will review our current understanding on the significance of pDCs in ameliorating inflammatory responses during herpes simplex virus keratitis, sterile inflammation, and corneal transplantation. Moreover, we describe their novel and pivotal neuroprotective role, their key function in preserving corneal angiogenic privilege, as well as their potential application as a cell-based therapy for ocular diseases. •The cornea, limbus, conjunctiva, choroid, retina, and lacrimal glands are endowed with resident plasmacytoid dendritic cells.•Corneal plasmacytoid dendritic cells secret type I interferons during herpes simplex virus-1 keratitis and limit viral propagation, dissemination to the corneal stroma, draining lymph nodes, and trigeminal ganglion. They also prevent re-programing of Tregs to effector ex-Tregs.•Corneal plasmacytoid dendritic cells promote graft survival by inhibiting effector Th1 cells in the draining lymph nodes after corneal transplantation.•Corneal plasmacytoid dendritic cells are pivotal for corneal nerve maintenance and function through secretion of neurotrophic molecules.•Resident plasmacytoid dendritic cells, which accompany limbal vessels, produce anti-angiogenic molecules and contribute to corneal angiogenic privilege.