Neutralization capacity of measles virus H protein specific IgG determines the balance between antibody-enhanced infectivity and protection in microglial cells

► We characterized infection-enhancing activity of IgG monoclonal antibodies (MAbs) against measles virus (MV) H protein. ► Partially neutralizing MAb CL55 enhanced MV infection in Fc receptor-expressing microglial cells. ► Strongly neutralizing MAb 20H6 enhanced MV infectivity in microglial cells only at sub-protective titers. ► At relevant protective titers, MAb 20H6 had a dominant blocking effect against antibody-enhanced MV infection. ► The antibody neutralization capacity determined the balance between protection and IgG-enhanced MV infectivity.