Cell surface regulators of complement, 512 antigen, and CD59, in the rat eye and adnexal tissues

PURPOSE. Cell surface complement regulatory proteins have been identified i n high levels in ocular tissues, but no experimental model is available for examining their physiological roles. To develop such a model, the distribu tion of 512 antigen, a protein possessing the functions of the human decay- accelerating factor (DAF [CD55]) and membrane cofactor protein (MCP [CD46]) , and rat inhibitory protein (CD59), the homologue of the human membrane in hibitor of reactive lysis (MIRL[CD59]) were characterized in the rat eye an d ocular adnexal structures. METHODS. After euthanasia of female Wistar rats, followed by orbital exente ration, eyelids and orbital tissue including the lacrimal gland were separa ted from the globes and immediately snap-frozen in liquid nitrogen at -70 d egrees C. Tissues then were sectioned at -20 degrees C and examined immunoh istochemically for 512 antigen and rat CD59. RESULTS. Both molecules were found to be present in high levels in multiple sites. Corneal and conjunctival epithelia showed moderate to intense label ing for both regulators. Fibroblasts in the corneal stroma, conjunctiva, an d sclera labeled similarly. Corneal endothelial cells showed intense labeli ng for rat CD59 but not for 512 antigen. The iris and ciliary body showed i ntense labeling for both proteins. The retina showed labeling at multiple l evels, with that of rat CD59 being more intense than that of 512 antigen. T he lacrimal gland labeled for both regulators. Vessels, muscle, and nerves in the orbit labeled intensely for both antigens. In the eyelid, conjunctiv a, sebaceous glands, and muscle and nerve tissues labeled moderately to int ensely for both molecules, whereas skin epithelium labeled less intensely. CONCLUSIONS. 512 antigen and rat CD59 are expressed in high levels and dist ributed similarly in the rat eye and lacrimal gland to DAF, MCP, and MIRL i n the human eye and lacrimal gland. These findings establish the rat ocular surface as a model for studying the role of cell surface complement regula tors in this site. This first identification of copious expression of these proteins in eyelid structures. which also participate in protection of the ocular surface, further suggests an important role for surface complement regulatory proteins in this location.