Current models of B lymphocyte biology posit that B cells continuously recirculate between lymphoid organs, without accumulating in peripheral healthy tissues. Nevertheless, B lymphocytes are one of the most prevalent leukocyte populations in the naive murine heart. To investigate this apparent inconsistency in the literature, we conducted a systematic analysis of myocardial B cell ontogeny, trafficking dynamics, histology, and gene expression patterns. We found that myocardial B cells represent a subpopulation of circulating B cells that make close contact with the microvascular endothelium of the heart and arrest their transit as they pass through the heart. The vast majority (>95%) of myocardial B cells remain intravascular, whereas few (<5%) myocardial B cells cross the endothelium into myocardial tissue. Analyses of mice with B cell deficiency or depletion indicated that B cells modulate the myocardial leukocyte pool composition. Analysis of B cell–deficient animals suggested that B cells modulate myocardial growth and contractility. These results transform our current understanding of B cell recirculation in the naive state and reveal a previously unknown relationship between B cells and myocardial physiology. Further work will be needed to assess the relevance of these findings to other organs.
Luigi Adamo, Cibele Rocha-Resende, Chieh-Yu Lin, Sarah Evans, Jesse Williams, Hao Dun, Wenjun Li, Cedric Mpoy, Prabhakar S. Andhey, Buck E. Rogers, Kory Lavine, Daniel Kreisel, Maxim Artyomov, Gwendalyn J. Randolph, Douglas L. Mann
Myocardial B cells are mostly intravascular and in intimate contact with the endothelium.