Immunohistochemical studies on meningoencephalitis in feline infectious peritonitis (FIP)

WANG, Huanan; HIRABAYASHI, Miyuki; CHAMBERS, James K.; UCHIDA, Kazuyuki; NAKAYAMA, Hiroyuki

In the present study, all the 4 cases examined were diagnosed as FIP based on the clinical and pathologic findings. Viral antigens were detected in macrophages around vessels of the lesions in the leptomeninges and subventricles of Case Nos. 1 to 3. These findings were in conformity with those in a recent report on FIP meningoencephalitis [15] . On the other hand, viral antigen was not detected in the brain of Case No. 4, though the cat was clinically diagnosed as FIP because of neurological symptoms and elevated antibody titer of FCoV. Pathological diagnosis of FIP is mainly performed by immunofluorescence (IF) using fresh tissues or immunohistochemistry on formalin-fixed paraffin sections [7] . Immunohistochemistry was believed to be more specific than IF [15] , while some previous reports also raised questions about its specificity [4] . The antibody used in this study, FIPV3-70, is known to react with the nucleocapsid antigen of FIPV and is considered a valuable diagnostic tool for FIP [8] . However, a previous paper demonstrated antigenic heterogeneity in FIPV nucleocapsid proteins [14] . Thus, it is possible that the difference in FIPV antigen type cause the lack of viral antigen in lesions of Case No. 4.