Multiple recurrences in melanin-protein-induced uveitis in the rat

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Abstract
The purpose of the present study was to investigate the occurrence and sequelae of multiple recurrences in experimental melanin-protein-induced uveitis (EMIU). Lewis rats were immunized with purified bovine choroidal melanin granules, and the development of EMIU was studied during six months. Multiple recurrences were observed in virtually all rats that developed primary EMIU. The spontaneous recurrences exhibited an increasingly mild character and a decreasing frequency over time. They occurred one to four times per eye with intervals of five to six weeks. If the inflammations were more severe or chronic the uveal tissues were more seriously damaged. The anterior uvea became slender by loss of cells and stroma during the process suggesting a role as target. Unlike in primary EMIU, the retina finally exhibited areas with damage of the photoreceptor and pigment epithelial cells. Mononuclear cells were the predominant inflammatory cell type in the entire uvea in eyes with serious recurrences or chronic uveitis. The number of recurrences per se did not correlate with the extent of tissue damage but the overall severity of the disease over six months did. In rats recovered from mild recurrences, a single injection of pertussis toxin, or melanin granules emulsified in Freund's incomplete adjuvant was sufficient to reinduce severe EMIU with extensive damage of the uvea. Hence, specific as well as aspecific stimulation of the immune system caused severe recurrences of this type of uveitis. EMIU resembles non-infectious human anterior uveitis in several respects, even in its multiple recurrences.