Complement Factor H-Related Proteins CFHR2 and CFHR5 Represent Novel Ligands for the Infection-Associated CRASP Proteins of Borrelia burgdorferi

Corinna Siegel,Barbara Uzonyi,Peter Kraiczy,Christine Skerka,Reinhard Wallich,Peter F Zipfel,Brian Stevenson,Tobias Beckhaus,Hannes Eberhardt,Teresia Hallström,Michael Karas

doi:10.1371/journal.pone.0013519

Abstract

BackgroundOne virulence property of Borrelia burgdorferi is its resistance to innate immunity, in particular to complement-mediated killing. Serum-resistant B. burgdorferi express up to five distinct complement regulator-acquiring surface proteins (CRASP) which interact with complement regulator factor H (CFH) and factor H-like protein 1 (FHL1) or factor H-related protein 1 (CFHR1). In the present study we elucidate the role of the infection-associated CRASP-3 and CRASP-5 protein to serve as ligands for additional complement regulatory proteins as well as for complement resistance of B. burgdorferi.Methodology/Principal FindingsTo elucidate whether CRASP-5 and CRASP-3 interact with various human proteins, both borrelial proteins were immobilized on magnetic beads. Following incubation with human serum, bound proteins were eluted and separated by Glycine-SDS-PAGE. In addition to CFH and CFHR1, complement regulators CFHR2 and CFHR5 were identified as novel ligands for both borrelial proteins by employing MALDI-TOF. To further assess the contributions of CRASP-3 and CRASP-5 to complement resistance, a serum-sensitive B. garinii strain G1 which lacks all CFH-binding proteins was used as a valuable model for functional analyses. Both CRASPs expressed on the B. garinii outer surface bound CFH as well as CFHR1 and CFHR2 in ELISA. In contrast, live B. garinii bound CFHR1, CFHR2, and CFHR5 and only miniscute amounts of CFH as demonstrated by serum adsorption assays and FACS analyses. Further functional analysis revealed that upon NHS incubation, CRASP-3 or CRASP-5 expressing borreliae were killed by complement.Conclusions/SignificanceIn the absence of CFH and the presence of CFHR1, CFHR2 and CFHR5, assembly and integration of the membrane attack complex was not efficiently inhibited indicating that CFH in co-operation with CFHR1, CFHR2 and CFHR5 supports complement evasion of B. burgdorferi.

Highlights

Lyme disease is the most commonly reported vector-borne infectious disease in Eurasia and the United States
Lyme disease spirochetes are highly resistant to killing by the host’s alternative pathway of complement [7,8]. This is accomplished, at least in part, by the spirochetes camouflaging their outer surface with host-derived complement factor H (CFH) and factor H-like protein 1 (FHL1) which are fluid-phase immune regulators of the alternative complement pathway [9,10,11,12]
Identification of serum proteins that bind to complement regulator-acquiring surface proteins (CRASP)-3 and CRASP-5

Summary

Introduction

Lyme disease is the most commonly reported vector-borne infectious disease in Eurasia and the United States. This multisystemic inflammatory disease is caused by species of the Borrelia burgdorferi sensu lato complex, which includes B. burgdorferi sensu stricto (s.s.), B. garinii, and B. afzelii [1]. Lyme disease spirochetes are highly resistant to killing by the host’s alternative pathway of complement [7,8] This is accomplished, at least in part, by the spirochetes camouflaging their outer surface with host-derived complement factor H (CFH) and factor H-like protein 1 (FHL1) which are fluid-phase immune regulators of the alternative complement pathway [9,10,11,12]. In the present study we elucidate the role of the infection-associated CRASP-3 and CRASP-5 protein to serve as ligands for additional complement regulatory proteins as well as for complement resistance of B. burgdorferi

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