Borrelia burgdorferi Outer Membrane Vesicles Contain Antigenic Proteins, but Do Not Induce Cell Death in Human Cells.

Kati Karvonen,Leona Gilbert,Jonna Nykky,Hanna Tammisto

doi:10.3390/microorganisms10020212

Abstract

Like many bacterial species, Borrelia burgdorferi, the pleomorphic bacterium that causes Lyme borreliosis, produces outer membrane vesicles (OMVs). Borrelial OMVs (BbOMVs) have been identified as containing virulence factors, such as outer surface proteins (Osps) A, B, and C, as well as DNA. However, the pathogenicity of BbOMVs in disease development is still unclear. In this study, we characterized purified BbOMVs by analyzing their size and immunolabeling for known antigenic markers: OspA, OspC, p39, and peptidoglycan. In addition, BbOMVs were cocultured with human non-immune cells for cytotoxicity analysis. The results demonstrated that, on average, the vesicles were small, ranging between 11 and 108 nm in diameter. In addition, both OspA and OspC, as well as Lyme arthritis markers p39 and peptidoglycan, were detected from BbOMVs. Furthermore, BbOMVs were cocultured with non-immune cells, which did not result in cell death. Combined, these results suggested that BbOMVs could participate in the induction of infection by functioning as a decoy for the host immune system. Furthermore, BbOMVs might serve as a means for persistent antigens to remain in the host for prolonged periods of time.

Highlights

Lyme borreliosis (LB), the most common vector-borne disease in North America and Europe [1], is caused by the pleomorphic spirochete bacteria Borrelia burgdorferi (B. burgdorferi) [2]
BbOMVs Were on Average 33 nm in Diameter
We examined the characteristics of borrelial outer membrane vesicles, and the possible cytotoxic consequences induced by these vesicles in human cells

Summary

Introduction

Lyme borreliosis (LB), the most common vector-borne disease in North America and Europe [1], is caused by the pleomorphic spirochete bacteria Borrelia burgdorferi (B. burgdorferi) [2]. Persistence of the bacterium or bacterial antigens in the host tissue are considered as one possible explanation for continued disease manifestations [5–10]. Bacterial outer membrane vesicles (OMVs) are produced in normal growth cultures by Gram-negative bacteria [11]. It is believed that OMVs are produced either by blebbing of the bacterial outer membrane or explosive cell lysis [12]. OMVs are spherical, 10–300 nm in size, and contain a single membrane bilayer [11,13]. OMVs consist of similar outer membrane proteins, polysaccharides, and lipids as the membranes of the originating bacterium, and can carry a variety of cargo, including genetic information [11,12,14]. OMVs have been identified from in vitro growth cultures, as well as in vivo animal and human fluid and tissue samples [15–20]. It has been suggested that OMVs function, for example, as a means for the bacterium to react to the surrounding environment, or in inter- and intracellular communication, the transport of biological signals far away from the originating bacterium, the removal of harmful factors

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