Cutting edge: Hierarchy of maturity of murine memory B cell subsets.

The paucity of murine memory B cell markers has been a significant impediment to the study of memory. The most commonly used marker is IgG, which is neither sensitive nor specific, because activated nonmemory cells can be IgG(+), and memory cells can be IgM(+). In this article, we show that, together, PD-L2 (CD273), CD80, and CD73 define at least five phenotypic subsets of murine memory B cells. These subsets are generated from naive cells bearing a single BCR in response to a single T-dependent Ag. This diversity is independent of class switch, because IgG(1)- and IgM-bearing memory cells are found within each compartment. Memory subsets defined by PD-L2, CD80, and CD73 are biologically distinct from one another, because they differ in ontogeny and selection. Together, these distinctions suggest that there is a spectrum of memory B cells and progressive acquisition from more naive-like to more memory-like properties.