Detection of Antigenic Heterogeneity in Feline Coronavirus Nucleocapsid in Feline Pyogranulomatous Meningoencephalitis

Abstract

Abstract.A new monoclonal antibody (mAb), CCV2-2, was compared with the widely used FIPV3-70 mAb, both directed against canine coronavirus (CCoV), as a diagnostic and research tool. Western blot showed that both anti-CCoV mAbs only reacted with a protein of 50 kD, a weight consistent with the feline coronavirus (FCoV) viral nucleocapsid. A competitive inhibition enzyme-linked immunosorbent assay showed that the 2 recognized epitopes are distinct. Preincubation of CCV2-2 mAb with FCoV antigen suppressed the immunostaining. Formalin-fixed, paraffin-embedded sections from brains of 15 cats with the dry form of feline infectious peritonitis (FIP) were examined by immunohistochemistry. Immunohistochemistry was performed with both anti-CCoV mAbs, either on consecutive or on the same sections. A myeloid-histiocytic marker, MAC 387, was also used to identify FIP virus-infected cells. In all regions where MAC 387-positive cells were present, positive staining with the CCV2-2 mAb was systematically detected, except at some levels in 1 cat. In contrast, none or only a few cells were positive for the FIPV3-70 mAb. Double immunostaining showed macrophages that were immunopositive for either CCV2-2 alone or alternatively for CCV2-2 and FIPV3-70 mAbs. This reveals the coexistence of 2 cohorts of phagocytes whose FIP viral contents differed by the presence or absence of the FIPV3-70-recognized epitope. These findings provide evidence for antigenic heterogeneity in coronavirus nucleocapsid protein in FIP lesions, a result that is in line with molecular observations. In addition, we provide for the first time morphologic depiction of viral variants distribution in these lesions.

A review of feline infectious peritonitis virus infection: 1963–2008

“…A recent published immunohistochemical study on brain lesions from 15 cats with the dry form of FIP used two different monoclonal antibodies directed against unrelated epitopes of CCV to search for variants. 137 These authors also used a myeloidhistiocytic marker, MAC387, to identify infected macrophages. Double immunostaining demonstrated macrophages that were positive for either the CCVmonoclonal antibody alone, or for both the CCVand FIPV-monoclonal antibodies.…”

Immunohistochemical studies on meningoencephalitis in feline infectious peritonitis (FIP)

“…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.…”

“…Lesions in the central nervous system (CNS) are frequently observed mainly in the leptomeninges, ventricles, choroid plexus and sometimes neuroparenchyma [5,12,16]. Although histopathological features of FIP lesions in the CNS have been well documented [6,14,15], the association between inflammatory cell types and the distribution of viral antigens remains to be clarified. The present study describes the inflammatory cell types and viral antigen distribution in the brain lesions of 4 cats diagnosed as FIP.…”

Non-tuberculous Mycobacteria can Cause Disseminated Mycobacteriosis in Cats

“…The secondary reagent was anti-mouse antibody polymer linked to horseradish peroxidase (BrightVision + Poly-HRP-anti Ms/Rb; Immunologic, Duiven, the Netherlands) with 3,3 0 -diaminobenzidine tetrahydrochloride as chromogen. The FIPV3-70 anti-coronavirus antibody is routinely used for diagnosis of feline infectious peritonitis (Kipar et al, 1998;Poncelet et al, 2008).…”