Characterization of T-lymphocytes in the anterior uvea of eyes with chronic equine recurrent uveitis

Equine recurrent uveitis (ERU), a chronic, recurrent inflammation primarily of the anterior uveal tract, is the most common cause of blindness in hors es. Recently, T-lymphocytes have been found to be the most numerous cell ty pe to infiltrate the anterior uveal of horses with ERU. In the present stud y, we characterized the T-lymphocyte population in the anterior uveal tract of eyes of horses with chronic ERU by evaluating the microscopic appearanc e (histopathologic features), the T-lymphocyte subsets, and the relative le vels and amounts of T-lymphocyte cytokine mRNA in the anterior uvea. Seven inflamed eyes (from six horses with chronic ERU) and 5 normal eyes (from fi ve horses with nonocular problems) were studied. After clinical examination , the eyes were removed, ocular fluids were aspirated, and anterior uveal t issues (iris and ciliary body) were processed for histologic and molecular (RNA isolation) analyses. Histologic examination by hematoxylin and eosin ( H and E) staining and immunohistochemistry evaluating T-lymphocyte subsets (anti-CD4, CD8, CD5) were performed for each sample. RNA samples were analy zed for levels of messenger (m) RNA specific for interleukin (IL)-2, 4, and interferon-gamma (IFN gamma) by quantitative reverse transcriptase polymer ase chain reaction (QRT-PCR). Eyes with ERU exhibited characteristic clinic al signs, including corneal edema, aqueous flare, posterior synechia, corpo ra nigra degeneration, and cataract formation. Histologically, infiltration of the uveal tract with lymphocytes, plasma cells, and macrophages was mos t evident in the ciliary body and base of the iris. Loss of tissue structur e (destruction) was most evident in the ciliary processes. Infiltrating lym phocytes were predominantly CD4+ T-cells (e.g. 48% CD4+ and 18% CD8+ in the ciliary body stroma), as determined by immunohistochemistry. Few inflammat ory cells were observed in the normal eyes. The QRT-PCR results revealed in creased transcription of IL-2 and IFN gamma and low IL-4 mRNA expression in eyes with chronic ERU compared to normal eyes, demonstrating a T-helper (T h) 1-like inflammatory response in eyes with ERU. (C) 1999 Elsevier Science B.V. All rights reserved.