Lymphocyte and antibody responses reduce enterovirus 71 lethality in mice by decreasing tissue viral loads

Enterovirus 71 (EV71) infects the central nervous system and causes death and long-term neurological sequelae in hundreds of thousands of young children, but its pathogenesis remains elusive. Immunopathological mechanisms have been suspected to contribute to the pathogenesis of neurological symptoms, so antiinflammatory agents have been used to treat patients with neurological symptoms. The present study was therefore designed to investigate the functions of lymphocyte and antibody responses in EV71 infection using a mouse model. Immunohistochemical staining analysis revealed virus and three types of lymphocytes, B cells, CD4 T cells, and CD8 T cells, in the spinal cord of an EV71-infected patient who died. A study of mice showed that the levels of virus and lymphocytes in brains and antibody titers in sera were elevated during the time when the mice succumbed to death in a phenomenon analogous to that observed in patients. Further studies demonstrated that after infection, the disease severity, mortality, and tissue viral loads of mice deficient in B, CD4 T, or CD8 T cells were significantly higher than those of wild-type mice. In addition, treatment with a virus-specific antibody, but not a control antibody, before or after infection significantly reduced the disease severity, mortality, and tissue viral loads of mice deficient in B cells. Our results show that both lymphocyte and antibody responses protect mice from EV71 infection. Our study suggests the use of vaccines and virus-specific antibodies to control fatal outbreaks and raises caution over the use of corticosteroids to treat EV71-infected patients with neurological symptoms.