LCMV-specific CD4 T cell dependent polyclonal B-cell activation upon persistent viral infection is short lived and extrafollicular.

Persistent virus infections with non- or poorly cytopathic viruses are commonly associated with B cell dysregulations. These include the induction of hypergammaglobulinemia and the emergence of virus-unspecific antibodies. These seemingly unspecific antibody responses interfere with the virus-specific humoral immunity and contribute to delayed virus control. Whether these virus-unspecific antibodies are induced in the B cell follicle or at extrafollicular sites and whether one specific CD4 T cell subset is involved in the polyclonal B cell activation is unclear. Here we studied virus-unrelated IgG antibody responses against self or foreign antigens in the context of persistent lymphocytic choriomeningitis virus (LCMV) infection. We found that the LCMV-unspecific antibody response is short-lived and induced predominantly at extrafollicular sites and depends on the presence of LCMV-specific CD4 T cells. Our data support a scenario in which activated, virus-specific CD4 T cells provide help to non-specific B cells at extrafollicular sites, supporting the production of virus unspecific IgG antibodies during persistent viral infection.