Selective Infection of Antigen-Specific B Lymphocytes by Salmonella Mediates Bacterial Survival and Systemic Spreading of Infection

Yuri Souwer,Tineke Jorritsma,Yotam E Bar-Ephraïm,Hans Janssen,Jelle De Wit,Elena Zagato,Jacques Neefjes,Maria Rescigno,S Marieke Van Ham,Alexander Griekspoor,Chiara Martinoli,Laurel L Lenz

doi:10.1371/journal.pone.0050667

Abstract

BackgroundThe bacterial pathogen Salmonella causes worldwide disease. A major route of intestinal entry involves M cells, providing access to B cell-rich Peyer’s Patches. Primary human B cells phagocytose Salmonella typhimurium upon recognition by the specific surface Ig receptor (BCR). As it is unclear how Salmonella disseminates systemically, we studied whether Salmonella can use B cells as a transport device for spreading.Methodology/Principal FindingsHuman primary B cells or Ramos cell line were incubated with GFP-expressing Salmonella. Intracellular survival and escape was studied in vitro by live cell imaging, flow cytometry and flow imaging. HEL-specific B cells were transferred into C57BL/6 mice and HEL-expressing Salmonella spreading in vivo was analyzed investigating mesenteric lymph nodes, spleen and blood. After phagocytosis by B cells, Salmonella survives intracellularly in a non-replicative state which is actively maintained by the B cell. Salmonella is later excreted followed by reproductive infection of other cell types. Salmonella-specific B cells thus act both as a survival niche and a reservoir for reinfection. Adoptive transfer of antigen-specific B cells before oral infection of mice showed that these B cells mediate in vivo systemic spreading of Salmonella to spleen and blood.Conclusions/SignificanceThis is a first example of a pathogenic bacterium that abuses the antigen-specific cells of the adaptive immune system for systemic spreading for dissemination of infection.

Highlights

Salmonella enterica is a Gram-negative, enteric pathogen responsible for diseases that lead to significant morbidity and mortality [1]
Cells in a Nonreplicative State We recently demonstrated that primary antigen-specific B cells phagocytose Salmonella typhimurium when the bacteria are recognized by the antigen-specific by the specific surface Ig receptor (BCR) [20]
Pre-incubation of primary B cells with F(ab)2 fragments of the anti-IgM antibody before exposure to antiIgM coated GFP-Salmonella dramatically reduces the amount of GFP-Salmonella positive B cells, demonstrating that phagocytosis of Salmonella by B cells is mediated by the BCR (Figure 1B)

Summary

Introduction

Salmonella enterica is a Gram-negative, enteric pathogen responsible for diseases that lead to significant morbidity and mortality [1]. The bacterium crosses the intestinal epithelium via transcytosis of specialized M cells [2] or via luminal capture by sampling dendritic cells [3,4]. Salmonella can infect most cell types to form an intracellular vacuole called the Salmonella-containing vacuole (SCV) Another set of effectors is introduced into the host cytosol for vacuole maintenance and interference with the endosomal system to obtain nutrients and to prevent maturation and fusion with lysosomes [8,9]. Primary human B cells phagocytose Salmonella typhimurium upon recognition by the specific surface Ig receptor (BCR). As it is unclear how Salmonella disseminates systemically, we studied whether Salmonella can use B cells as a transport device for spreading

Methods

Results

Conclusion