Glial response in the central nervous system of cats with feline infectious peritonitis

Objectives The aim of the study was to evaluate central nervous system (CNS) lesions in non-effusive and effusive cases of feline infectious peritonitis (FIP) regarding aspects related to astrocytic and microglial reactions. Methods Five necropsied cats that were naturally infected with FIP virus, confirmed by reverse transcriptase polymerase chain reaction and immunohistochemistry, with different intensities of CNS lesions, were studied. Brain and cerebellum were evaluated by light microscopy and immunohistochemistry for glial fibrillary acidic protein (GFAP) and vimentin to assess astrocytic morphology, and lectin histochemistry for Ricinus communis agglutinin-I (RCA-I) to detect microglia was performed to evaluate the glial response in the CNS of cats with FIP. Results An important astrocytic response in many areas of the CNS of all cats, including the periventricular areas of lateral ventricles and fourth ventricle, the molecular layer of the cerebellum and cerebral cortex, was visualized. This astrocytic reactivity was associated with areas of granulomatous or pyogranulomatous vasculitis/perivasculitis in most cases, and it was characterized by multifocal to coalescing astrocytosis and astrogliosis with an increase in the expression of intermediate filaments, such as GFAP. However, astrocytes exhibited strong vimentin expression in neuroparenchyma with severe inflammatory and necrotic changes, but GFAP expression was mild or absent in these cases. A microglial response was present only in severe lesions, and RCA-I expression was detected primarily in gitter cells and resting microglia. Conclusions and relevance The present study indicates a strong astrocytic response, including the presence of many less differentiated vimentin-positive astrocytes and gitter cells positive for RCA-1 in severe lesions in the CNS of cats with FIP.