Multiple players in mouse B cell memory

• Multiple memory B-cell subsets are generated by the immune response.
• IgM+ and IgG+ memory B cells fullfill different effector functions.
• Early memory B cells emerge as germinal center-independent subpopulations.
• Persisting germinal centers modify the outcome of the recall response.

B cell memory has long been considered the attribute of the sole IgG-positive B cell subset. Since a few years, and due to new B-cell subset identification procedures, increasing heterogeneity has been identified among the memory B cell pool. IgM-positive cells and germinal center-independent subsets are recent additions to the field. This review describes the diversity of memory B cells, as well as controversial issues on their relative contribution to the recall response. The impact of a protracted germinal center response to the specific mobilization of IgM memory B cells is proposed.