Memory B and plasma cells (PCs) are generated in the germinal center (GC). As PD-1 is highly expressed in T follicular helper cells (TFH), we investigated the role of PD-1 signaling in the humoral response. We found that PD-L1 and PD-L2 are upregulated on GC B cells. Pdcd1lg2−/−, CD274−/−Pdcd1lg2−/− and Pdcd1−/− mice had reduced numbers of long-lived PCs. The mechanism involved increased GC cell death and decreased TFH cytokine production in the absence of PD-1; the effect was selective, as remaining PCs had higher affinity. PD-1 expression on T cells and PD-L2 expression on B cells controlled TFH and PC numbers. Thus, PD-1 regulates selection and survival in the GC, impacting the quantity and quality of long-lived PCs.

Memory B cells (MBCs) are long-lived sources of rapid, isotype-switched secondary antibody-forming cell (AFC) responses. Whether MBCs homogeneously retain the ability to self-renew and terminally differentiate or if these functions are compartmentalized into MBC subsets has been unclear. It was previously suggested that antibody isotype controls MBC differentiation upon restimulation. Here we demonstrate that subdividing MBCs based on expression of CD80 and PD-L2, independent of isotype, identified MBC subsets with distinct functional behaviors upon rechallenge. CD80+PD-L2+ MBCs differentiated rapidly into AFCs but did not generate germinal centers (GCs); conversely CD80−PD-L2− MBCs generated few early AFCs but robustly seeded GCs. Gene expression patterns of subsets support both the identity and function of these distinct MBC types. Hence, MBC differentiation and regeneration are compartmentalized.

Immunological memory is the residuum of a successful immune response that in the B cell lineage comprises long-lived plasma cells and long-lived memory B cells. It is apparent that distinct classes of memory B cells exist, distinguishable by, among other things, immunoglobulin isotype, location, and passage through the germinal center. Some of this variation is due to the nature of the antigen, and some appears to be inherent to the process of forming memory. Here, we consider the heterogeneity in development and phenotype of memory B cells and whether particular functions are partitioned into distinct subsets. We consider also how understanding the details of generating memory may provide opportunities to develop better, functionally targeted vaccines.