A prominent feature of atherosclerosis is the production of antibodies to oxLDL. Numerous studies suggest that antibodies to oxLDL can be atheroprotective, but recent evidence demonstrates that B cell responses can promote atherogenesis. Overall, the data suggest that antibodies to oxLDL can modulate atherosclerosis. These antibodies can modulate inflammation by interacting with Fc receptors expressed on the surface of various immune cells, in particular, dendritic cells (DC). The overall aim of this proposal is to understand how antibodies to oxLDL can regulate the inflammatory response in atherosclerosis by modulating DC function. The role of DC in atherogenesis has not been fully elucidated. Furthermore, while FcRs have been implicated in the uptake of oxLDL immune complexes (IC) and modulation of inflammatory pathways in macrophages, the role of oxLDL/IC in modulating DC function through FcRs has not been investigated. We hypothesized that a) oxLDL immune complexes activate DC by interacting with FcRs, and that b) the inhibitory FcRIIb protects against atherosclerosis by downmodulating DC inflammatory responses to oxLDL/IC conveyed through FcRI/III and TLR4. To test this, we propose the following specific aims: Specific Aim 1. To test the hypothesis that oxLDL-immune complexes activate a pro- inflammatory pathway in DC. In this aim, we will use bone marrow-derived DC from wild type mice to determine whether in vitro stimulation with heat-aggregated oxLDL/IC induce activation of DC. Specific Aim 2. To test the hypothesis that the inhibitory FcRIIb downregulates inflammatory responses by DC in response to oxLDL-immune complexes. In this aim we will determine whether FcRIIb downregulates oxLDL/IC positive signaling through TLR4 and FcRI/III using BM-derived myeloid DC from wild type and TLR4-, FcRI/III- and FcRIIb-deficient mice. Specific Aim 3. To evaluate the contribution of FcR-mediated signaling in DC in modulating immune responses in atherosclerosis in vivo. To determine whether FcRIIb protects against atherosclerosis by downregulating DC activation in vivo, we will adoptively transfer in vitro generated wild type, FcRI/III-deficient, FcRIIb-deficient and TLR4-deficient DC into CD11c-/-apoE-/- mice. To further investigate the role of FcR-mediated modulation of DC function in atherosclerosis, we will adoptively transfer DC that have been activated in vitro with oxLDL/IC into CD11c-/-apoE-/- mice. To our knowledge, this is the first study addressing immune complex-mediated signaling on DC and modulation of atherosclerosis. The experiments proposed herein will help elucidate the role of antibody responses to oxLDL in atherosclerosis by addressing their effect in DC function. Our results will lead to the identification of cellular (DC) and/or molecular (FcRs) therapeutics for the modulation of atherosclerosis.