Variant proteins stimulate more IgM+ GC B-cells revealing a mechanism of cross-reactive recognition by antibody memory.

Bronwen R Burton,Richard W Titball,John Love,Richard K Tennant,David C Wraith,Harry N White

doi:10.7554/elife.26832

Bronwen R Burton, Richard W Titball + Show 4 more

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https://doi.org/10.7554/elife.26832

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Abstract

Vaccines induce memory B-cells that provide high affinity secondary antibody responses to identical antigens. Memory B-cells can also re-instigate affinity maturation, but how this happens against antigenic variants is poorly understood despite its potential impact on driving broadly protective immunity against pathogens such as Influenza and Dengue. We immunised mice sequentially with identical or variant Dengue-virus envelope proteins and analysed antibody and germinal-centre (GC) responses. Variant protein boosts induced GCs with a higher proportion of IgM+ B cells. The most variant protein re-stimulated GCs with the highest proportion of IgM+ cells with the most diverse, least mutated V-genes and with a slower but efficient serum antibody response. Recombinant antibodies from GC B-cells showed a higher affinity for the variant antigen than antibodies from a primary response, confirming a memory origin. This reveals a new process of antibody memory, that IgM memory cells with fewer mutations participate in secondary responses to variant antigens, demonstrating how the hierarchical structure of B-cell memory is used and indicating the potential and limits of cross-reactive antibody based immunity.

Highlights

Antibody-based immunity is underpinned by memory B-cells that have undergone antibody somatic hyper-mutation (SHM) and selection for improved antigen binding in germinal centres (GCs) (MacLennan et al, 1997)
Binding to E3 correlates with binding to E4, but because of the generally low recombinant antibodies (rAbs) affinities we suggest that the antibodies cannot discriminate between similar epitopes
IgM rAbs cloned from E4 boost day 7 GC showed a higher affinity for E4 than those from E4 primed day 7 GC, implying they were memory derived

Summary

Introduction

Antibody-based immunity is underpinned by memory B-cells that have undergone antibody somatic hyper-mutation (SHM) and selection for improved antigen binding in germinal centres (GCs) (MacLennan et al, 1997). Re-challenge with the same antigen stimulates a rapid, higher affinity, secondary antibody response. Memory B-cells of IgM and IgG isotypes can re-instigate GCs after secondary exposure (Dogan et al, 2009; Pape et al, 2011; McHeyzer-Williams et al, 2015), but how this happens against variant antigens is poorly understood despite its potential impact on driving the most broadly protective immunity. It has long been speculated that this diversity may facilitate the recognition of antigenic variants (Herzenberg et al, 1980; Pape et al, 2011; Kaji et al, 2012) which could stimulate secondary Several studies suggest diversity in the memory B-cell population, showing that cells can express IgM or IgG (Dogan et al, 2009; Pape et al, 2011), be mutated or non-mutated (Kaji et al, 2012) and have low affinities (Smith et al, 1997), but still persist in GCs (Kuraoka et al, 2016).

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