Immunosuppressive properties of tissues of the ocular anterior segment.

To determine whether explants of various tissues comprising the anterior segment of individual normal eyes can display immunosuppressive properties in vitro, explants of iris/ciliary body, cornea, cornea-limbus, sclera and conjunctiva were prepared from single eyes of BALB/c mice and tested for their capacity to suppress alloantigen-driven T cell activation in vitro. Cultured explants of iris and ciliary body, and of cornea, but not sclera or conjunctiva, suppressed T cell activation in vitro. Similarly, the supernatants of cultured iris/ciliary body and cornea explants displayed immunosuppressive properties. Prostaglandins appeared to make a minor contribution to the inhibition observed. The authors conclude that certain tissues within the anterior segment of the eye (iris, ciliary body, cornea) contain cells that secrete immunosuppressive factors, whereas other tissues (conjunctiva, sclera) lack this feature. The secretions of the former tissues undoubtedly contribute to the immunosuppressive features of the microenvironment in the anterior segment of the eye, and help to account for the existence of immune privilege.