Abstract 221: B-1b Cells Produce IgM to Malondialdehyde-Modified Low Density Lipoprotein in Perivascular Adipose Tissue in Response to Immunization And Attenuate Diet Induced Atherosclerosis

Abstract

Background: B-1b cells are capable of long-lasting IgM memory and secrete more IgM, particularly malondialdehyde-modified low density lipoprotein (MDA-LDL) specific IgM than B-1a cells after transfer into hyperlipidemic Rag1 -/- mice. Id3 is a basic helix-loop-helix protein and dominant negative inhibitor of E proteins. B cell specific Id3 deficiency (Id3 BKO ) increases B-1b cell numbers systemically and provides atheroprotection. Adipose tissue is a source of B-1b-derived IgM and regulates inflammatory cytokine production from M1 macrophages locally. Perivascular adipose tissue (PVAT) has been implicated in regulation of atherosclerosis. However, the effect of B cell specific Id3 deficiency on B-1 cell responses in PVAT is not yet known. Also, whether these B-1b cells respond to MDA-LDL immunization is unknown. Hypothesis: B-1b cells are present in PVAT and produce MDA-LDL specific IgM in PVAT, and immunization with MDA-LDL can enhance B-1b-mediated atheroprotection. Methods and Results: Flow Cytometry and Enzyme-Linked ImmunoSpot (ELISPOT) analysis of PVAT of normal chow diet fed young mice demonstrated that ApoE.Id3 BKO mice have significantly higher numbers of B-1b cells and IgM secreting cells but not B-2 and B-1a cell numbers in PVAT compared to ApoE.Id3 WT mice. ELISPOT demonstrated that the % of MDA-LDL specific IgM of total IgM secreting cells was significantly greater in PVAT, but not in spleen or bone marrow, of ApoE.Id3 BKO mice compared to ApoE.Id3 WT mice, suggesting that modified lipids such as MDA-LDL in plaques and PVAT may stimulate local B-1b cells to secrete MDA-LDL specific IgM. Adoptive transfer of B-1b cells into ApoE.Rag1 -/- mice followed by MDA-LDL+PPS3 (pneumococcal polysaccharide) immunization, increased plasma IgM to MDA-LDL after 2 weeks and significantly attenuated atherosclerosis after 16 weeks of Western diet compared to PBS injected mice and B-1b cells transferred mice with PBS immunization. Conclusion: B-1b cells produce IgM to MDA-LDL in PVAT. MDA-LDL immunization increased IgM to MDA-LDL after two weeks and attenuated diet-induced atherosclerosis. Taken together, results suggest that B-1b cells may regulate atherosclerosis through both local and systemic IgM production.