Immune evasion of Borrelia miyamotoi: CbiA, a novel outer surface protein exhibiting complement binding and inactivating properties

Abstract

Borrelia (B.) miyamotoi, an emerging tick-borne relapsing fever spirochete, resists complement-mediated killing. To decipher the molecular principles of immune evasion, we sought to identify determinants contributing to complement resistance. Employing bioinformatics, we identified a gene encoding for a putative Factor H-binding protein, termed CbiA (complement binding and inhibitory protein A). Functional analyses revealed that CbiA interacted with complement regulator Factor H (FH), C3, C3b, C4b, C5, and C9. Upon binding to CbiA, FH retained its cofactor activity for Factor I-mediated inactivation of C3b. The Factor H-binding site within CbiA was mapped to domain 20 whereby the C-terminus of CbiA was involved in FH binding. Additionally, CbiA directly inhibited the activation of the classical pathway and the assembly of the terminal complement complex. Of importance, CbiA displayed inhibitory activity when ectopically produced in serum-sensitive B. garinii G1, rendering this surrogate strain resistant to human serum. In addition, long-term in vitro cultivation lead to an incremental loss of the cbiA gene accompanied by an increase in serum susceptibility. In conclusion, our data revealed a dual strategy of B. miyamotoi to efficiently evade complement via CbiA, which possesses complement binding and inhibitory activities.

The Complement Binding and Inhibitory Protein CbiA of Borrelia miyamotoi Degrades Extracellular Matrix Components by Interacting with Plasmin(ogen)

“…His 6 -tagged CbiA originated from B. miyamotoi and BBA70, DbpA, and CspA from B. burgdorferi were produced as previously described (Benoit et al, 2011 ; Koenigs et al, 2013 ; Hammerschmidt et al, 2014 ; Röttgerding et al, 2017 ). To generate His 6 -tagged CbiA proteins with single, double, triple, and quadruple amino acid substitutions, PCR was performed with primers designed for site-directed mutagenesis (Supplementary Table 1 ; Kraiczy et al, 2009 ).…”

“…To generate His 6 -tagged CbiA proteins with single, double, triple, and quadruple amino acid substitutions, PCR was performed with primers designed for site-directed mutagenesis (Supplementary Table 1 ; Kraiczy et al, 2009 ). Plasmid pQE-CbiA (Röttgerding et al, 2017 ) was used as template for introducing single amino acid substitutions R145A, K153A, K154A, R156A, K162A, R185A, and K188A. For double substitutions K154A-K162A, plasmid pQE-CbiA K154A and for simultaneous mutations K154A-K162A-K188A, plasmid pQE-CbiA K154A-K162A was used as templates.…”

“…In order to establish an infection, the spirochetes must overcome the host complement system as an essential part of innate immunity and indeed B. miyamotoi exhibit a remarkable resistance to complement-mediated killing (Teegler et al, 2014 ; Wagemakers et al, 2014 ; Margos et al, 2015 ). More recently, CbiA, a complement-inhibitory protein, has been identified that interacts with complement in multiple ways, binding distinct complement components including key complement regulator Factor H (FH), C3, C3b, C4b, and C5 and thereby terminating activation of distinct complement pathways (Röttgerding et al, 2017 ).…”

Borrelia miyamotoi: 43 Cases Diagnosed in France by Real-Time PCR in Patients With Persistent Polymorphic Signs and Symptoms

“…The frequency of B. miyamotoi, as a human pathogen, as well as the severity of some related signs and symptoms such as meningoencephalitis, make prevention, diagnosis and treatment of this infection essential (21). Furthermore, B. Miyamotoi may be resistant to some antibiotics such as amoxicillin, at least in vitro and has the ability to bypass the body's immune mechanisms, such as the complement by means of a surface protein, a factor H-binding protein, termed CbiA (complement binding and inhibitory protein A) (22)(23)(24). The local immune response is influenced by the tick, which secretes a multitude of immunosuppressive salivary factors that target the organism defense molecules.…”

Line Immunoblot Assay for Tick-Borne Relapsing Fever and Findings in Patient Sera from Australia, Ukraine and the USA

“…Another putative RFB-specific candidate for differential diagnosis is a surface exposed lipoprotein termed the Borrelia immunogenic protein A or BipA [40,41]. A third potential RFB-specific candidate antigen is another surface lipoprotein that binds factor H and a related factor H-like protein (termed the factor H binding protein or fHbp) and helps protect RFB from human complement-mediated killing through activation of the alternative pathway of complement [42][43][44]. Additionally, GlpQ and proteins of approximate molecular masses similar to BipA (70-75kDa) and fHbp (20-23kDa) were identified as being able to detect RFB-specific antibodies in WBs performed on whole cell lysates of B. hermsii and B. turcica [25,45].…”