Intricate targeting of immunoglobulin somatic hypermutation maximizes the efficiency of affinity maturation

Helper T cell-regulated B cell immunity

In this review, we will discuss the cascade of cellular and molecular events in the immune response to protein antigens that regulate the development of high-affinity B cell memory. The behavior of antigen-experienced pMHCII+ dendritic cells DCs and the dynamics of their interaction with specific T-helper (Th) cells define the first developmental checkpoint for adaptive immunity in vivo. Recent studies provide insight into the basis of Th cell clonal selection and the requirements and consequences of antigen priming in this responsive Th cell compartment. Antigen-specific Th cells expand to become the cognate regulators of effector B cell responses and initiators of the germinal center reaction and memory B cell development. We will discuss the development and role of these diverse mixtures of antigen-specific B cells in the control of B cell memory and long-term humoral immunity that underpin effective protein vaccination.

Latest technologies for the enhancement of antibody affinity

High affinity antibodies are crucial both for the discovery and validation of biomarkers for human health and disease and as clinical diagnostic and therapeutic reagents. This review describes some of the latest technologies for the design, mutation and selection of high affinity antibodies that provide a paradigm for molecular evolution of a far wider range of proteins including enzymes. Strategies include both in vivo and in vitro methods and embrace the latest concepts for antibody display and selection. Specifically, affinity enhancement can be tailored to the target-binding surface, typically the complementary determining region (CDR) loops in antibodies, whereas enhanced stability, expression or catalytic properties can be affected by selected changes to the core protein scaffold. Together, these technologies provide a rapid and powerful strategy to drive the next generation of protein-based reagents for numerous clinical, environmental and agribusiness applications.

The mismatch repair protein Msh6 influences the in vivo AID targeting to the Ig locus

Somatic hypermutation (SHM) and class switch recombination (CSR) are initiated by activation-induced cytidine deaminase (AID), which preferentially deaminates deoxycytidines at WRC (W = A/T, R = A/G) motifs in vitro. The mechanisms responsible for targeting AID and for organizing the queue of enzymes involved in vivo have been elusive. Here, we examined point mutant knockin Msh6 mice (Msh6(TD/TD)), which lack the second phase of SHM but retain all the proteins involved, and found that AID was frequently targeted to non-WRC motifs. Unexpectedly, by comparing SHM and CSR in wild-type, Msh6(TD/TD), and age-matched Msh6(-/-) mice, we discovered that the presence of Msh6 protein influenced the AID targeting in phase one of SHM and mediated the proper targeting of recombination sites in CSR in vivo. Our data suggest that Msh6 plays a scaffolding role in the first phase of SHM, in addition to its enzymatic role in the second phase of SHM.

Peripheral B cells latently infected with Epstein-Barr virus display molecular hallmarks of classical antigen-selected memory B cells

Epstein-Barr virus (EBV) establishes a lifelong persistent infection within peripheral blood B cells with the surface phenotype of memory cells. To date there is no proof that these cells have the genotype of true germinal-center-derived memory B cells. It is critical to understand the relative contribution of viral mimicry versus antigen signaling to the production of these cells because EBV encodes proteins that can affect the surface phenotype of infected cells and provide both T cell help and B cell receptor signals in the absence of cognate antigen. To address these questions we have developed a technique to identify single EBV-infected cells in the peripheral blood and examine their expressed Ig genes. The genes were all isotype-switched and somatically mutated. Furthermore, the mutations do not cause stop codons and display the pattern expected for antigen-selected memory cells based on their frequency, type, and location within the Ig gene. We conclude that latently infected peripheral blood B cells display the molecular hallmarks of classical antigen-selected memory B cells. Therefore, EBV does not disrupt the normal processing of latently infected cells into memory, and deviations from normal B cell biology are not tolerated in the infected cells. This article provides definitive evidence that EBV in the peripheral blood persists in true memory B cells.