Acute and anamnestic B cell responses to west nile virus infection .

摘要

The collective purpose of all immune cells is to recognize and eliminate foreign pathogens. While some effector cells have transient functions early after infection, memory cells can persist for years to protect the host from future challenge. In general, B lymphocytes mediate protection via the secretion of antibody, however B cells are a diverse population encompassing many specialized subsets. Certain B cell populations are activated early after infection, whereas others are important for the maintenance of immunological memory long after the pathogen is cleared. Previous studies using a mouse model of West Nile virus (WNV) infection indicated that B cells are critical for control of viral dissemination and survival. However, the importance of the early and memory B cell response during infection were not well understood.;These studies dissect the requirements and significance of early B cell activation, and the functional roles of memory B cells (MBC) and long-lived plasma cells (LLPC) in response to variant viruses. These studies revealed that after WNV infection lymph node B cells were highly activated as measured by upregulation of CD69, CD86 and MHC-II. Activation was dependent on sustained signaling through the IFN-alphabeta receptor and partially dependent on expression of TLR3, MyD88, and class II MHC. Furthermore, activation was polyclonal, as mice with a single B cell receptor (BCR) specificity (HEL-Ig mice) were equivalently activated after infection. Although B cell activation peaked at day 3 after infection, antigen-specific IgM-secreting cells were not detected until 7 days after infection. To test if phagocytic cells were important for activation of B cells, mice were treated with clodronate liposomes and B cell activation was evaluated. B cells were activated normally in the absence of lymph node macrophages, however phagocytic cells were required for restricting WNV replication and survival from infection. Thus, robust polyclonal B cell activation occurs via an IFN-alphabeta receptor-dependent, but macrophage and BCR-independent mechanism early after WNV infection.;After infection is cleared, LLPC and MBC persist to protect the host from future challenge with the same or related pathogens. The second aim of this study addressed the importance of MBC and LLPC after WNV infection. Bone marrow resident LLPC were highly specific for a dominant neutralizing epitope that comprises residues K307 and T330 on the envelope protein. Consequently, LLPC antibody poorly neutralized a variant virus with a mutation introduced within this epitope (WNV-K307E). We found that MBC, in contrast to LLPC, were enriched in specificities that recognized the variant epitope. This observation was consistent with the ability of MBC antibody to equivalently neutralize wild type and variant WNV. Finally, adoptive transfer experiments revealed that MBC respond WNV-K307E infection by secreting antibody skewed away from the K307/T330 epitope. This data supports a model in which LLPC are poised to respond to homologous viral infection, while MBC are better suited to control variant virus infection.