Signaling events resulting from synchronous BCR and CD180 activation on murine B cells differ from activating CD180 or the BCR alone

Abstract

Abstract CD180 (RP105), expressed on dendritic cells and B cells, is a receptor closely related to TLR4. CD180 signaling does not require adaptor proteins like MyD88, instead it resembles B cell receptor (BCR) signaling, including the activation of PI3K and Akt. Recently, others and we have found αCD180 also induces the Pim-1 kinase, but much of the CD180 signaling pathway remains ill defined. We previously found that targeting antigen (Ag) to B cells via CD180, by coupling the Ag to an anti-CD180 antibody (Ag-αCD180), induces a rapid and strong Ag-specific IgG antibody (Ab) response in mice. Furthermore, IgG Ab responses were maintained in immunodeficient mice that lack mature B cells (BAFFR−/−). These studies led us to investigate the signaling events that occur within B cells upon coincident activation of the BCR and CD180. For this study we have employed B1-8hi transgenic mice, which have a BCR that binds to NP-hapten on some splenic B cells, and the K46μm17 murine B cell line, that expresses both CD180 and an NP-specific BCR. By stimulating these NP-specific B cells with αCD180, NP-isotype Ab control or an NP-αCD180 conjugate, we are defining the signaling elements specific to the activation of the BCR and CD180 together vs. single receptor ligation only. Utilizing these models, we are working to characterize the survival and proliferation signals induced, including Pim-1 and Akt, and to phenotype the B cell expansion in mice following NP-αCD180 vaccination. Data will be presented showing how CD180-BCR co-ligation differs from signaling through either receptor alone. These studies will enhance our understanding of how CD180 Ag targeting is able to induce strong humoral responses even in immunodeficient mice. (Supported by NIH grant R01AI44257).