Analysis of the mechanism of antibody-dependent enhancement of feline infectious peritonitis virus infection: aminopeptidase N is not important and a process of acidification of the endosome is necessary

Abstract

Infection of the monocyte/macrophage lineage with feline infectious peritonitis virus (FIPV) is enhanced in the presence of anti-FIPV antibodies (antibody-dependent enhancement or ADE). We investigated the following unclear points concerning ADE of FIPV infection: (i) involvement of the virus receptor, feline aminopeptidase N (fAPN), in ADE activity in FIPV infection; (ii) necessity of acidification of the endosome in cellular invasion of FIPV. Virus receptor-blocking experiments using anti-fAPN antibodies at 4 or 37 6C and experiments using fAPN-negative U937 cells revealed that fAPN is not involved in ADE of FIPV infection. Experiments using lysosomotropic agents clarified that acidification of the endosome is necessary for cellular invasion by FIPV, regardless of the presence or absence of antibodies. These findings may be very important for understanding the mechanism of ADE of FIPV infection. Feline infectious peritonitis virus (FIPV) is classified as a feline coronavirus (FCoV).FCoVs have a single-stranded, positive-sense, linear RNA genome and are mainly composed of nucleocapsid (N), transmembrane and spike (S) proteins (Olsen, 1993). FCoVs are classified into types I and II according to their S protein properties (Hohdatsu et al., 1991a;Motokawa et al., 1995Motokawa et al., , 1996. FCoVs are also classified into two biotypes based on differences in pathogenicity: feline enteric coronavirus (FECV) and FIPV. FECV is asymptomatic in cats, but FIPV infection induces feline infectious peritonitis (FIP). FIP is a fatal disease in wild and domestic cat species, mainly leading to the development of immune complex vasculitis. There are types I and II FECV and FIPV in FCoV. Type II FCoVs are known to utilize feline aminopeptidase N (fAPN) as virus receptor (Hohdatsu et al., 1998).FIPV targets the monocyte/macrophage lineage, infection of which is enhanced in the presence of antibodies (antibodydependent enhancement or ADE). ADE activity in FIPV infection is induced when anti-FIPV-S antibody-bound viruses infect cells of the monocyte/macrophage lineage by binding to the Fc portion of Fc receptors on the cell surface Hohdatsu et al., 1991b;Olsen et al., 1992). When anti-FIPV-S antibodies are absent, FIPV infects the monocyte/macrophage lineage via fAPN (Rottier et al., 2005). However, whether the virus receptor, fAPN, is involved in ADE of FIPV infection is not clear.It has been reported that mouse hepatitis virus type 2 (MHV-2) and severe acute respiratory syndrome coronavirus (SARS-CoV) enter cells through a low pH-dependent, endosomal pathway (Qiu et al., 2006;Simmons et al., 2005). Van Hamme et al. (2007) studied the kinetics of binding and internalization, demonstrating clearly that FIPV enters the cell via endocytosis. However, it is unclear whether acidification of the endosome is necessary for cellular invasion by FIPV, regardless of the presence or absence of antibodies. In this study, we investigated the involvement of the virus receptor (fAPN) in ADE of FIPV infection and the necessity of acidification of...

Identification and characterisation of small molecule inhibitors of feline coronavirus replication

“…Using an IFA-based time of addition study involving a single replication cycle we were able to further clarify of the effect of time of addition, and refine the possible stage of the viral life cycle targeted by each compound. Based on the IFA results chloroquine was effective only if present at the time of infection, supporting the hypothesis that chloroquine acts during cell entry for FCoV FIPV1146, possibly through inhibition of endosomal pH (Takano et al, 2008). Hexamethylene amiloride and mefloquine provided significant antiviral effects when compound addition was delayed for up to 1 and 5 hpi respectively, suggesting that if the antiviral effects of these compounds arise through perturbation of endosomal function, the effects occur at different stages of the viral life cycle.…”

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

“…In this scenario, virusinfected macrophages overproduce B-cell differentiation/survival factors, which in turn act to promote B-cell differentiation into plasma cells. This same group 235 also investigated key steps in ADE in FIP such as involvement of the virus receptor and the requirement for acidification of the endosome for cellular invasion. They concluded that aminiopeptidatse N was not required for antibody enhancement.…”

Clathrin- and serine proteases-dependent uptake of porcine epidemic diarrhea virus into Vero cells

“…Similarly, TGEV binds to porcine APN (Weingartl and Derbyshire, 1994), and has been shown to enter MDCK cells over-expressing porcine APN via endocytosis and acidification of the intracellular compartment facilitated membrane fusion (Hansen et al, 1998). FIPV also requires acidification of endosomes for successful entry (Takano et al, 2008). Inhibition of FIPV infection with nystatin, a pharmacological reagent that causes caveolae to flatten and disrupt the coat structure, and dynamin 2 inhibitor suggests that FIPV entry might actually involve some types of caveolae-dependent endocytosis (Van Hamme et al, 2008).…”