Transforming growth factor-β levels in aqueous humor during experimentally induced uveitis

The anterior chamber of the eye is known to be a site of immune privilege. Particularly, the aqueous humor (AqH) appears to possess unique immunoregulatory properties. The authors have previously shown that human AqH (HAqH) may increase or decrease the proliferation of different cell types. Although no single factor has been established as solely responsible for these effects, much attention has been given to the 24-30 kD fraction of AqH, where transforming growth factor-beta (TGF-β) is found. The purpose of this study was to determine the changes occurring in the rabbit AqH (RAqH) in relation to intraocular inflammation. Heterologous lens or human serum albumin (HSA) immunization-induced uveitis models were used in two groups of New Zealand albino rabbits to study the relationship between uveitis and TGF-β. AqH and serum samples were obtained serially before, during and after the induction of ocular inflammation. Systemic humoral immunity to HSA or lens antigens was monitored using enzyme-linked immunosorbent assay (ELISA). A mink lung epithelial cell (CCL-64) bioassay for TGF-β was used to quantify the amount of this cytokine in RAqH. TGF-β levels in RAqH increased fourfold after the first immunization. A sharp decrease in RAqH TGF-β levels was found in association with the development of acute intraocular inflammation. The implications of this finding to the etiology of uveitis are discussed.