Early B-cell activation after West Nile virus infection requires alpha/beta interferon but not antigen receptor signaling.

The B-cell response against West Nile virus (WNV), an encephalitic Flavivirus of global concern, is critical to controlling central nervous system dissemination and neurological sequelae, including death. Here, using a well-characterized mouse model of WNV infection, we examine the factors that govern early B-cell activation. Subcutaneous inoculation with a low dose of replicating WNV results in extensive B-cell activation in the draining lymph node (LN) within days of infection as judged by upregulation of the surface markers CD69, class II major histocompatibility complex, and CD86 on CD19(+) cells. B-cell activation in the LN but not the spleen was dependent on signals through the type I alpha/beta interferon (IFN-alpha/beta) receptor. Despite significant activation in the draining LN at day 3 after infection, WNV-specific B cells were not detected by immunoglobulin M enzyme-linked immunospot analysis until day 7. Liposome depletion experiments demonstrate that B-cell activation after WNV infection was not affected by the loss of F4/80(+) or CD169(+) subcapsular macrophages. Nonetheless, LN myeloid cells were essential for control of viral replication and survival from infection. Overall, our data suggest that the massive, early polyclonal B-cell activation occurring in the draining LN after WNV infection is immunoglobulin receptor and macrophage independent but requires sustained signals through the type I IFN-alpha/beta receptor.