Supplementary Components1. B cells (MBCs), which provide protection against antigen re-exposure1C3, can differentiate into antibody-forming cells (AFCs) and make new antibodies, or enter germinal centers (GCs) and provide a renewed source of lasting B cell immunity. Despite the importance of MBCs for vaccine- and infection-induced protection4C6, we have a limited understanding of the nature of these cells and how they participate in secondary responses. Based on expression microarray comparisons between MBCs and na?ve B cells, we identified several surface proteinsincluding CD80 previously, Compact disc73thead wear and PD-L2 are portrayed exclusively about MBCs and serve to divide MBCs into multiple phenotypic subsets7. We have centered on subpopulations of MBCs described by manifestation of both B7 family, Compact disc80 and PD-L2. These subsets differ in several properties: Compact disc80?PD-L2?, double-negative (DN) MBCs, possess hardly any mutations7 fairly,8. CD80+PD-L2+, double-positive (DP) MBCs have the most mutations, and CD80?PD-L2+ single-positive (SP) MBCs have an intermediate mutational content7,8. Although all subsets contain cells expressing surface B cell receptors of the immunoglobulin M (IgM) or switched IgG isotypes, the DN Lp-PLA2 -IN-1 subset is predominantly IgM+, and the SP and DP populations contain progressively more IgG+ cells. These two featuresmutation and isotype switchwhich are both irreversible DNA alterations that occur during the primary response, indicate that the Lp-PLA2 -IN-1 memory populations are stable and that cells do not move from one population to another (otherwise mutational content and switching would equalize between the populations). Classically, B cell secondary responses generate rapid effector function, most likely by quickly converting MBCs to AFCs9. This raises the question of how the memory compartment undergoes self-renewal in the face of terminal differentiation of MBCs into AFCs. Though it is unclear how MBCs are homeostatically maintained, stem cell gene expression signatures have been identified in MBCs10C12. It has been proposed that self-renewing MBCs represent a discrete population that can differentiate into both plasma cells and GC B cells after antigen re-exposure10,11. If this were the case, it is possible that either all MBCs retain self-renewal as well as terminal differentiation potential, with the fate of the cell being determined by environmental cues13. Alternatively, these functions may be segregated into different dedicated subsets of MBCs, which may be pre-programmed to respond differently even upon identical stimuli. Lately two organizations possess recommended how the MBC pool can be divided by antibody isotype manifestation functionally, either IgM or turned IgG14,15. They discovered that isotype-switched MBCs differentiated into AFCs while IgM+ MBCs produced fresh GCs. From these total outcomes they suggested that surface area isotype demonstrates fundamental variations in MBC potential, and recommended that signaling variations between IgG+ and IgM+ cells could govern different practical reactions16,17. On a parallel track, we proposed that the subsets defined by CD80 and PD-L2 expression represent a spectrum of MBC commitment, with the PRKM10 DN cells being more na?ve-like and the DP cells more memory-like9. Expression of these subset markers on murine MBCs has been confirmed by others in different systems17C20. We hypothesized that upon reactivation the more memory-like DP MBCs will differentiate quickly into effector cells that function by providing new AFCs and not GCs, and that more na?ve-like DN MBCs will make new GCs thus renewing the memory pool by providing a new source of cellular immunity. Here we have tested these hypotheses by examining the function after reactivation of MBC populations distinguished by CD80 and PD-L2 expression, while controlling for isotype expression. We generated, purified and transferred these MBC subsets with and without T cells and assessed their Lp-PLA2 -IN-1 ability to make AFCs and GCs upon reexposure to antigen. We found substantial functional heterogeneity that was independent of isotype, but dependent on subset markers. Hence, MBC functional heterogeneity is not determined by BCR isotype, as thought, but rather by cell intrinsic features that are captured by the expression of key surface area markers. This watch of the structure from the MBC area provides implications for monitoring immune system states and therefore for vaccine advancement. Results Generating, testing and purifying.