Interaction of Staphylococci with Human B cells

RESEARCH ARTICLE Interaction of Staphylococci with Human B cells Tyler K. Nygaard1, Scott D. Kobayashi1, Brett Freedman1, Adeline R. Porter1, Jovanka M. Voyich2, Michael Otto3, Olaf Schneewind4, Frank R. DeLeo1* 1 Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America, 2 Department of Microbiology and Immunology, Montana State University, Bozeman, Montana, United States of America, 3 Laboratory of Bacteriology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America, 4 Department of Microbiology, University of Chicago, Chicago, Illinois, United States of America a11111 * Abstract OPEN ACCESS Citation: Nygaard TK, Kobayashi SD, Freedman B, Porter AR, Voyich JM, Otto M, et al. (2016) Interaction of Staphylococci with Human B cells. PLoS ONE 11(10): e0164410. doi:10.1371/journal. pone.0164410 Editor: Tarek Msadek, Institut Pasteur, FRANCE Received: June 8, 2016 Accepted: September 23, 2016 Published: October 6, 2016 Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Data Availability Statement: All relevant data are within the paper. Funding: This work was supported by the Intramural Research Program of the National Institute of Allergy and Infectious Diseases, National Institutes of Health and a grant from the National Institutes of Health (NIH-R01A1090046 to JMV). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Staphylococcus aureus is a leading cause of human infections worldwide. The pathogen produces numerous molecules that can interfere with recognition and binding by host innate immune cells, an initial step required for the ingestion and subsequent destruction of microbes by phagocytes. To better understand the interaction of this pathogen with human immune cells, we compared the association of S. aureus and S. epidermidis with leukocytes in human blood. We found that a significantly greater proportion of B cells associated with S. epidermidis relative to S. aureus. Complement components and complement receptors were important for the binding of B cells with S. epidermidis. Experiments using staphylococci inactivated by ultraviolet radiation and S. aureus isogenic deletion mutants indicated that S. aureus secretes molecules regulated by the SaeR/S two-component system that interfere with the ability of human B cells to bind this bacterium. We hypothesize that the relative inability of B cells to bind S. aureus contributes to the microbe’s success as a human pathogen. Introduction Staphylococcus aureus is a ubiquitous Gram-positive bacterium capable of causing life-threatening disease in humans and animals alike. This prominent pathogen has remained a major cause of morbidity and mortality despite the advent of antibiotic therapy [1]. For example, there are an estimated 72,444 cases of invasive MRSA infection and 9,194 associated patient deaths in the United States annually [2]. The need to advance novel therapeutic strategies to successfully treat S. aureus infection is further underscored by the high burden of communityassociated MRSA (CA-MRSA) in the US [3]. Distinct CA-MRSA lineages appear to have obtained beta-lactam resistance via horizontal acquisition of mecA on multiple separate occasions outside of the healthcare setting [4], and are noted for their enhanced virulence relative to some of the most successful healthcare-associated MRSA (HA-MRSA) lineages. Despite PLOS ONE | DOI:10.1371/journal.pone.0164410 October 6, 2016 1 / 17 Staphylococci and B Cells extensive efforts for more than 100 years [5], attempts to vaccinate humans against S. aureus infections have repeatedly failed in clinical trials [6]. The ability of S. aureus to cause disease is largely attributed to the expression of an extensive and often redundant array of virulence genes that includes various toxins, adhesins, and immunomodulatory proteins. In addition, numerous S. aureus virulence molecules are believed to interfere with binding and subsequent phagocytosis of invading bacteria by host immune cells. The expression of these virulence molecules in vivo is largely coordinated by the concerted influence of two-component sensory systems, 16 of which have been putatively identified by sequence analysis within the S. aureus genome [7]. Of these two-component systems, the accessory gene regulator (Agr) and the regulator of S. aureus exoprotein expression (SaeR/S) are perhaps the best studied. Many S. aureus virulence genes, and extracellular toxins in particular, are under regulation by Agr and/or SaeR/S. The ingestion of bacteria by phagocytes is primarily initiated by the engagement of type I Fc receptors and complement receptors with corresponding opsonins on the bacterial surface. S. aureus expresses two proteins, S. aureus protein A (Spa) and immunoglobulin G-binding protein (Sbi), that can inhibit binding of S. aureus specific IgG with Fc receptors [8, 9]. A number of other secreted proteins, including staphylococcal complement inhibitor (SCIN) and extracellular fibrinogen-binding protein (Efb), have the capacity to inhibit the complement pathway to prevent deposition of activated C3 and C4 derivatives on the bacterial surface [10]. Compared to the closely related and common skin commensal Staphylococcus epidermidis, the large number of proteins expressed by S. aureus that have the ability to interfere with Fc and complement receptor binding suggests that blocking the action of these receptors is an important component of S. aureus fitness. An extensive body of research has elucidated the activity of these proteins in vitro and examined their importance in animal models of S. aureus infection. However, much less is known about the concerted influence of these immune evasion molecules on S. aureus pathogenesis during human infection. To better understand the influence of S. aureus virulence molecules on the recognition of bacteria by human immune cells, we investigated the interaction of S. aureus and S. epidermidis with leukocytes in human blood ex vivo. These studies revealed a significant difference in the association of S. aureus with human B cells relative to S. epidermidis or zymosan. Inactivation of S. aureus with ultraviolet irradiation promoted its association with human B cells, while an S. aureus mutant lacking genes encoding SaeR/S bound to human B cells in a manner seemingly indistinguishable from that of S. epidermidis. The association of B cells with S. epidermidis was found (...truncated)