Correlation between histopathological, clinical and biochemical parameters in S-antigen-induced experimental autoimmune uveitis in guinea-pigs

Footpad immunization with purified bovine retinal S-antigen in complete Freund's adjuvant was used to induce experimental allergic uveitis in 32 guinea-pigs. Thirteen animals immunized only with complete Freund's adjuvant were used as controls. Ninety-three point seven per cent of the animals immunized with S-antigen developed clinical experimental allergic uveitis while none of the controls had any clinical manifestation of uveitis. Histopathological analysis in the experimental group revealed mono- and polymorphonuclear cell infiltration in the choroid, ciliary body and iris. Simultaneous disruption of the outer segment of photoreceptor cell layer was also noticed. For the anterior segment of the eye there was a strong correlation between the histopathological grading and the clinical grading. For the posterior segment this correlation was, however, poor. Histopathological changes in the eye were correlated with the clinical grading and biochemical parameters (phospholipase A 2, prostaglandin E 2, leukotriene C 4, proteins and myeloperoxidase) measured from aqueous humour, serum samples and ciliary body-iris homogenate. Protein and phospholipase A 2 levels in the aqueous humour correlated well with the histological grading of the anterior segment of the eye. The myeloperoxidase activity, measured from ciliary body-iris homogenate, also correlated with the inflammatory cell infiltration in the anterior segment. Leukotriene C 4 and prostaglandin E 2 levels in aqueous humour did not correlate with the histopathological, or with the clinical grading, although elevated mean values were recorded in eyes having uveitis. Gamma glutamyl transpeptidase, measured in the serum, had a poor correlation with the histological grading for the anterior segment. All other parameters, measured in serum, did not correlate with the histopathological or the clinical grading. Histopathological changes in the anterior uvea are thus reflected by elevated protein and phospholipase A 2 levels in aqueous humour as well as by myeloperoxidase activity in ciliary body-iris homogenate.