Canine Distemper Virus Epithelial Cell Infection Is Required for Clinical Disease but Not for Immunosuppression

Abstract

To characterize the importance of infection of epithelial cells for morbillivirus pathogenesis, we took advantage of the severe disease caused by canine distemper virus (CDV) in ferrets. To obtain a CDV that was unable to enter epithelial cells but retained the ability to enter immune cells, we transferred to its attachment (H) protein two mutations shown to interfere with the interaction of measles virus H with its epithelial receptor, human nectin-4. As expected for an epithelial receptor (EpR)-blind CDV, this virus infected dog and ferret epithelial cells inefficiently and did not cause cell fusion or syncytium formation. On the other hand, the EpR-blind CDV replicated in cells expressing canine signaling lymphocyte activation molecule (SLAM), the morbillivirus immune cell receptor, with similar kinetics to those of wild-type CDV. While ferrets infected with wild-type CDV died within 12 days after infection, after developing severe rash and fever, animals infected with the EpR-blind virus showed no clinical signs of disease. Nevertheless, both viruses spread rapidly and efficiently in immune cells, causing similar levels of leukopenia and inhibition of lymphocyte proliferation activity, two indicators of morbillivirus immunosuppression. Infection was documented for airway epithelia of ferrets infected with wild-type CDV but not for those of animals infected with the EpR-blind virus, and only animals infected with wild-type CDV shed virus. Thus, epithelial cell infection is necessary for clinical disease and efficient virus shedding but not for immunosuppression.

Nectin-4-Dependent Measles Virus Spread to the Cynomolgus Monkey Tracheal Epithelium: Role of Infected Immune Cells Infiltrating the Lamina Propria

“…While a safe and efficient inactivated polio vaccine is available, efforts to develop an inactivated MV vaccine ceased in the 1960s, after a formalin-inactivated formulation was associated with more severe disease (35). The lack of shedding associated with the N4-blind MV observed here and the complete absence of clinical disease seen in ferrets infected with a nectin-4-blind CDV (27) provide proof of concept for the use of N4-blind MV during the late stages of the eradication campaign, when accidental transmission to naïve contacts can become increasingly problematic.…”

“…incompetence to infect epithelia prevented development of rash, fever, and gastrointestinal clinical signs (27). Thus, for CDV virulence in ferrets, nectin-4-dependent spread has more severe consequences than it does for MV virulence in monkeys.…”

“…To generate a virus incapable of epithelial spread (26,27), the MV hemagglutinin mutations impairing nectin-4-dependent cell entry were transferred to the hemagglutinin of a CDV causing lethal disease in ferrets (27). Animal studies confirmed the importance of epithelial cell infection for virus shedding and revealed that ϩ , and nucleocapsid ϩ cells in the trachea.…”

Nectin-4 Interactions Govern Measles Virus Virulence in a New Model of Pathogenesis, the Squirrel Monkey (Saimiri sciureus)

“…Thus, this species is a promising model to investigate the underlying mechanisms. The contribution of nectin-4 interactions to morbillivirus pathogenesis has been previously investigated in macaques and ferrets infected with nectin-4-blind derivatives of MeV and CDV, respectively (13,14,18). In ferrets, the wild-type and nectin-4-blind viruses initially caused the same extent of infection in immune tissues and resulted in similar levels of immunosuppression (18).…”

“…Even though an MeV unable to interact with nectin-4 is not shed into the airways of infected macaques, its virulence did not differ from that of the wild-type strain, since a mild rash and short-lasting anorexia were the only clinical signs (13). An analogously constructed nectin-4-blind canine distemper virus (CDV), a related morbillivirus that causes lethal disease in ferrets, did spread efficiently throughout the immune system and caused severe immunosuppression but no infection of epithelial tissues and no clinical disease (18).…”