AUTHOR=Srikakulapu Prasad , Upadhye Aditi , Drago Fabrizio , Perry Heather M. , Bontha Sai Vineela , McSkimming Chantel , Marshall Melissa A. , Taylor Angela M. , McNamara Coleen A. 

TITLE=Chemokine Receptor-6 Promotes B-1 Cell Trafficking to Perivascular Adipose Tissue, Local IgM Production and Atheroprotection

JOURNAL=Frontiers in Immunology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2021.636013

DOI=10.3389/fimmu.2021.636013

ISSN=1664-3224

ABSTRACT=<p>Chemokine receptor-6 (CCR6) mediates immune cell recruitment to inflammatory sites and has cell type-specific effects on diet-induced atherosclerosis in mice. Previously we showed that loss of CCR6 in B cells resulted in loss of B cell-mediated atheroprotection, although the B cell subtype mediating this effect was unknown. Perivascular adipose tissue (PVAT) harbors high numbers of B cells including atheroprotective IgM secreting B-1 cells. Production of IgM antibodies is a major mechanism whereby B-1 cells limit atherosclerosis development. Yet whether CCR6 regulates B-1 cell number and production of IgM in the PVAT is unknown. In this present study, flow cytometry experiments demonstrated that both B-1 and B-2 cells express CCR6, albeit at a higher frequency in B-2 cells in both humans and mice. Nevertheless, B-2 cell numbers in peritoneal cavity (PerC), spleen, bone marrow and PVAT were no different in <italic>ApoE</italic><sup>−/−</sup><italic>CCR6</italic><sup>−/−</sup> compared to <italic>ApoE</italic><sup>−/−</sup><italic>CCR6</italic><sup>+/+</sup> mice. In contrast, the numbers of atheroprotective IgM secreting B-1 cells were significantly lower in the PVAT of <italic>ApoE</italic><sup>−/−</sup><italic>CCR6</italic><sup>−/−</sup> compared to <italic>ApoE</italic><sup>−/−</sup><italic>CCR6</italic><sup>+/+</sup> mice. Surprisingly, adoptive transfer (AT) of CD43<sup>−</sup> splenic B cells into B cell-deficient μ<italic>MT</italic><sup>−/−</sup><italic>ApoE</italic><sup>−/−</sup> mice repopulated the PerC with B-1 and B-2 cells and reduced atherosclerosis when transferred into <italic>ApoE</italic><sup>−/−</sup><italic>CCR6</italic><sup>+/+</sup><italic>sIgM</italic><sup>−/−</sup> mice only when those cells expressed both CCR6 and sIgM. CCR6 expression on circulating human B cells in subjects with a high level of atherosclerosis in their coronary arteries was lower only in the putative human B-1 cells. These results provide evidence that B-1 cell CCR6 expression enhances B-1 cell number and IgM secretion in PVAT to provide atheroprotection in mice and suggest potential human relevance to our murine findings.</p>