Identifying the human B cell population that produces atheroprotective natural antibodies

Abstract

Abstract B cells act in a subset-dependent fashion in the development of murine atherosclerosis: conventional B-2 cells are atherogenic, while B-1 B cells have atheroprotective functions, mainly through production of IgM natural antibodies. Many of these antibodies are specific for oxidation-specific epitopes (OSE) such as malondialdehyde (MDA) on LDL and block macrophage uptake of oxidized lipids, preventing foam cell formation. In human subjects, high levels of plasma IgM to MDA-LDL are associated with reduced coronary artery disease and cardiovascular events; however the human B cell subset that produces these antibodies has not yet been identified. Recently, a putative human B-1 cell (CD20+CD27+CD43+) was defined. In PBMC from a cohort of human subjects presenting with cardiovascular disease, we show that expression of the chemokine receptor CXCR4 on human B-1 cells (n=54) positively correlated with plasma levels of IgM to MDA-LDL (p=0.004) and is inversely associated with coronary artery plaque volume as measured by intravascular ultrasound (IVUS) (p=0.0001). Using CyTOF mass cytometry technology, we demonstrate that CXCR4 expression was localized to a specific subset of human B-1 cells, suggesting that these cells may have distinct effector functions. Additionally, we developed biotinylated MDA-LDL and demonstrate that MDA-LDL showed enriched binding to a subset of IgM+ human B-1 cells, suggesting that these cells are responsible for producing IgM to MDA-LDL. Ongoing experiments will examine antibody production from these cells. Identification of the human cell type that produces IgM to MDA-LDL has the potential to lead to the development of strategies to enhance production of this atheroprotective antibody.