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

Here we describe tissue-resident memory B lymphocytes of spleen and bone marrow. Single cell transcriptomes and B cell receptor repertoires identify several exclusive populations of isotype-switched memory B cells (Bsm) in murine spleen and bone marrow, and one interconnected population of 10-20%. A population of marginal zone-like Bsm is located exclusively in the spleen while a novel population of quiescent Bsm is located exclusively in the bone marrow. Cells of two further populations, present in both, spleen and bone marrow, differ in repertoire between the two organs, i.e. are resident as well. Finally, another interconnected population of Bsm of the B1 lineage is present in spleen and bone marrow. In the bone marrow, all Bsm individually dock onto VCAM1+ stromal cells, resting in terms of activation, proliferation and mobility. The discrete B cell memory of bone marrow may be key to rapid secondary humoral responses to systemic antigens.