Inadequate Binding of Immune Regulator Factor H Is Associated with Sensitivity ofBorrelia lusitaniaeto Human Complement

Abstract

Spirochetes belonging to the Borrelia burgdorferi sensu lato complex differ in resistance to complementmediated killing by human serum. Here, we characterize complement sensitivity of a panel of B. lusitaniae isolates derived from ticks collected in Germany and Portugal as well as one patient-derived isolate, PoHL. All isolates are highly susceptible to complement-mediated lysis in human serum and activate complement predominantly by the alternative pathway, leading to an increased deposition of complement components C3, C6, and the terminal complement complex. Interestingly, serum-sensitive B. lusitaniae isolates were able to bind immune regulator factor H (CFH), and some strains also bound CFH-related protein 1 (CFHR1) and CFHR2. Moreover, CFH bound to the surface of B. lusitaniae was inefficient in mediating C3b conversion. Furthermore, the identification and characterization of a potential CFH-binding protein, OspE, revealed that this molecule possesses a significantly reduced binding capacity for CFH compared to that of CFH-binding OspE paralogs expressed by various serum-resistant Borrelia species. This finding suggests that a reduced binding capability of CFH is associated with an increased serum sensitivity of B. lusitaniae to human complement.

Borrelia valaisiana Resist Complement-Mediated Killing Independently of the Recruitment of Immune Regulators and Inactivation of Complement Components

“…Most of the complement-positive spirochetes showed extensive bleb formation when exposed to human serum, while a few cells stained negative for complement but were positive in the DAPI stain. Those spirochetes most likely represent “cell ghost” as previously described for serum susceptible B. garinii and B. lusitaniae strains [43], [49]. When spirochetes were incubated with heat-inactivated NHS, the cell morphology remained completely intact and deposition of complement was not detectable by immunofluorescence microscopy (data not shown).…”

“…Irrespective of whether they displayed a serum-sensitive or resistant phenotype, all three B. valaisiana isolates acquired CFHR-1 and strain Bv9, in addition, also bound CFHR2 from human serum. Despite binding of these complement regulators, Bv9 and VS116 failed to regulate complement activation, thus permitting bacteriolysis as previously shown for B. lusitaniae [49]. More interestingly, isolate ZWU3 Ny3 bound neither complement regulators of the alternative pathway CFH and FHL1, nor of the classical and lectin pathways, C4Bp and C1-Inh, respectively.…”

“…It has recently been shown that spirochetes of the B. burgdorferi sensu lato-complex exhibit a high diversity in their susceptibility pattern to human complement [23], [29], [46], [47], [49], [53]–[56]. Concerning serum susceptibility of B. valaisiana , the isolates investigated so far showed a serum-sensitive phenotype [53], [56], [57].…”

Contribution of the Infection-Associated Complement Regulator-Acquiring Surface Protein 4 (ErpC) to Complement Resistance ofBorrelia burgdorferi

“…Interaction with CFH has previously been reported for CRASP-4/ErpC and other closely related Erp proteins, for example, OspE paralogs from B. burgdorferi , B. afzelii , B. spielmanii , B. garinii , B. lusitaniae , B. turdi , B. tanukii , and B. japonica [3, 6, 11, 12, 33, 35, 37, 38, 43, 51, 55–58]. Here we demonstrate that recombinant CRASP-4 bound CFH in ELISA or ligand affinity blot experiments using borrelial cell lysates (Figures 2 and 3(b)).…”

TRIF Mediates Toll-Like Receptor 2-Dependent Inflammatory Responses to Borrelia burgdorferi

“…In addition, the complete abrogation of activation of inflammatory signaling in the absence of MyD88 implied that TLR2 did not activate a MyD88-independent pathway for signaling (19,20). However, more recently, multiple studies have shown that TLR2 is present in intracellular compartments and is involved in signaling from these compartments (3,(21)(22)(23)(24)(25)(26). Stimulation with TLR2 specific lipopeptides was shown to lead to the activation of type I interferons and proinflammatory cytokines, such as IL-6, whose activation and release was dependent on endosomal acidification (23,26).…”