Abstract

Staphylococcus aureus, a common cause of serious and often fatal infections, is well-armed with secreted factors that disarm host immune defenses. Highly expressed in vivo during infection, Staphylococcal protein A (SpA) is reported to also contribute to nasal colonization that can be a prelude to invasive infection. Co-evolution with the host immune system has provided SpA with an Fc-antibody binding site, and a Fab-binding site responsible for non-immune superantigen interactions via germline-encoded surfaces expressed on many human BCRs. We wondered whether the recurrent exposures to S. aureus commonly experienced by adults, result in the accumulation of memory B-cell responses to other determinants on SpA. We therefore isolated SpA-specific class-switched memory B cells, and characterized their encoding VH : VL antibody genes. In SpA-reactive memory B cells, we confirmed a striking bias in usage for VH genes, which retain the surface that mediates the SpA-superantigen interaction. We postulate these interactions reflect co-evolution of the host immune system and SpA, which during infection results in immune recruitment of an extraordinarily high prevalence of B cells in the repertoire that subverts the augmentation of protective defenses. Herein, we provide the first evidence that human memory responses are supplemented by B-cell clones, and circulating-antibodies, that bind to SpA determinants independent of the non-immune Fc- and Fab-binding sites. In parallel, we demonstrate that healthy individuals, and patients recovering from S. aureus infection, both have circulating antibodies with these conventional binding specificities. These findings rationalize the potential utility of incorporating specially engineered SpA proteins into a protective vaccine.

Highlights

  • Staphylococcus aureus (S. aureus) is a common commensal and opportunistic pathogen that is a frequent cause of communityand hospital-acquired diseases, including skin and soft tissue infections (SSTI), pneumonia, bacteremia, and endocarditis [1]

  • From a PBMC sample from a healthy adult donor without history of recent S. aureus infection, using our sorting panel, we captured conventional memory CD27+ IgG+ B cells and gated for binding activity of the SpAKK-tetramer (Figure 2B). With these selected B cells, we used droplet technology for single-cell recovery and sequencing of the naturally VH : VL paired gene rearrangements that accurately retained the sequences of the respective CH1 and CL domains (Figure 2C)

  • Our current studies provided an indepth examination of the relationships, defined by binding interactions, between human memory B cells with Staphylococcal protein A (SpA)

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Summary

Introduction

Staphylococcus aureus (S. aureus) is a common commensal and opportunistic pathogen that is a frequent cause of communityand hospital-acquired diseases, including skin and soft tissue infections (SSTI), pneumonia, bacteremia, and endocarditis [1]. Despite attempts with many different Staphylococcal protein and polysaccharide antigens, there is no approved preventative vaccine [5, 6]. Together these factors have contributed to the mounting societal burden of S. aureus infections, and the urgency for enhancing our understanding host-pathogen relationship with this microbial pathogen. A predominance of evidence indicates that in most individuals, recovery from infection is not accompanied by persistent enhanced immune defenses against future S. aureus infection [15,16,17,18,19]

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