Discrete populations of isotype-switched memory B lymphocytes are maintained in murine spleen and bone marrow

Abstract

At present, it is not clear how memory B lymphocytes are maintained over time, and whetheronly as circulating cells or also residing in particular tissues. Here we describe distinctpopulations of isotype-switched memory B lymphocytes (Bsm) of murine spleen and bonemarrow, identified according to individual transcriptional signature and B cell receptorrepertoire. A population of marginal zone-like cells is located exclusively in the spleen, while apopulation of quiescent Bsm is found only in the bone marrow. Three further residentpopulations, present in spleen and bone marrow, represent transitional and follicular B cellsand B1 cells, respectively. A population representing 10-20% of spleen and bone marrowmemory B cells is the only one qualifying as circulating. In the bone marrow, all cells individuallydock onto VCAM1+ stromal cells and, reminiscent of resident memory T and plasmacells, are void of activation, proliferation and mobility.