Immunohistochemical characterization of feline lymphoplasmacytic anterior uveitis

To characterize the immune cells present in different forms of feline anterior uveitis.

Eyes were obtained from 49 cats diagnosed with chronic idiopathic lymphoplasmacytic anterior uveitis, 7 cats with feline infectious peritonitis (FIP), and 9 cats euthanized for nonocular disease.

H&E sections were scored on the level of infiltrate in the anterior uvea. Immunohistochemistry was performed for FoxP3, CD3, and IL-17A, and positive cells were quantified in multiple images of each sample. A generalized estimating equation tested for an association between the level of inflammation and the prevalence of these cell types.

Cells stained positive for IL-17A in idiopathic uveitis but not in FIP samples. We found significantly fewer FoxP3⁺ and CD3⁺ cells in low-grade compared with high-grade inflammation in idiopathic uveitis or FIP samples (P values all <.005), but no difference between FIP and high-grade samples.

Idiopathic, but not FIP-associated, uveitis appears to have Th17 cell involvement. The numbers of FoxP3⁺ and CD3⁺ T-cells present appear directly correlated; thus, the severity of disease does not appear directly determined by the numbers of regulatory cells.