Feline infectious peritonitis (FIP) is a serious, widely distributed systemic disease caused by feline coronavirus (FCoV), in which ocular disease is common. However, questions remain about the patterns of ocular inflammation and the distribution of viral antigen in the eyes of cats with FIP. This study characterized the ocular lesions of FIP including the expression of glial fibrillary acidic protein and proliferating cell nuclear antigen by Müller cells in the retina in cases of FIP and to what extent macrophages are involved in ocular inflammation in FIP. Immunohistochemistry for FCoV, CD3, CD79a, glial fibrillary acidic protein, calprotectin, and proliferating cell nuclear antigen was performed on paraffin sections from 15 naturally occurring cases of FIP and from controls. Glial fibrillary acidic protein expression was increased in the retina in cases of FIP. Müller cell proliferation was present within lesions of retinal detachment. Macrophages were present in FIP-associated ocular lesions, but they were the most numerous inflammatory cells only within granulomas (2/15 cats, 13%). In cases of severe inflammation of the ciliary body with damage to blood vessel walls and ciliary epithelium (3/15, 20%), some macrophages expressed FCoV antigens, and immunolabeling for calprotectin on consecutive sections suggested that these FCoV-positive macrophages were likely to be recently derived from blood. In cases of severe and massive inflammation of most ocular structures (4/15, 26%), B cells and plasma cells predominated over T cells and macrophages. These results indicate that gliosis can be present in FIP-affected retinas and suggest that breakdown of the blood-ocular barrier can allow FCoV-bearing macrophages to access the eye.

Summary The avian pineal is a photosensory organ taking part in the organization of circadian and seasonal rhythms and playing an important role in the regulation of many behavior and physiological phenomena. The morphology of the pineal organ shows an enormous diversity. The aim of study was to investigate the histology and ultrastructure of the pineal organ in the Muscovy duck (Cairina moschata). The study was performed on 14-week-old females kept under natural lighting. The investigated pineals consisted of a wide distal part and narrow middle and proximal parts. The proximal part was attached to the diencephalon via the choroid plexus. The light microscopy showed a mixed structural form of the organ, which comprised both tubulo-follicular and solid parts. The stroma contained the lymphatic tissue, which occurred in a diffused form and as lymphoid nodules. Electron microscopy revealed the huge complexity of the parenchyma architecture, caused by the presence of several lumen-containing structures. According to their size and shape, they were classified into classical follicles, canals (diameter > 1 m) and canaliculi (diameter < 1 m). Pinealocytes were characterized by high variability of their shapes and sizes, frequently occurring partial or total reduction of the apical protrusions and presence of extremely numerous microtubules. The supporting cells constituted a prominent part of the pineal parenchyma and were represented by ependymal-like cells and astrocyte-like cells. Ependymal-like cells limited the lumen of follicles, canals and canaliculi.