CspA-Mediated Binding of Human Factor H Inhibits Complement Deposition and Confers Serum Resistance in Borrelia burgdorferi

Abstract

Borrelia burgdorferi has developed efficient mechanisms for evading the innate immune response during mammalian infection and has been shown to be resistant to the complement-mediated bactericidal activity of human serum. It is well recognized that B. burgdorferi expresses multiple lipoproteins on its surface that bind the human complement inhibitors factor H and factor H-like protein 1 (FH/FHL-1). The binding of FH/FHL-1 on the surface of B. burgdorferi is thought to enhance its ability to evade serum-mediated killing during the acute phase of infection. One of the key B. burgdorferi FH/FHL-1 binding proteins identified thus far was designated CspA. While it is known that CspA binds FH/FHL-1, it is unclear how the interaction between CspA and FH/FHL-1 specifically enhances serum resistance. To better understand how CspA mediates serum resistance in B. burgdorferi, we inactivated cspA in a virulent strain of B. burgdorferi. An affinity ligand blot immunoassay and indirect immunofluorescence revealed that the CspA mutant does not efficiently bind human FH to its surface. Consistent with the lack of FH binding, the CspA mutant was also highly sensitive to killing by human serum. Additionally, the deposition of complement components C3, C6, and C5b-9 was enhanced on the surface of the CspA mutant compared to that of the wild-type strain. The combined data lead us to conclude that the CspA-mediated binding of human FH confers serum resistance by directly inhibiting complement deposition on the surface of B. burgdorferi.

Versatile Roles of CspA Orthologs in Complement Inactivation of Serum-Resistant Lyme Disease Spirochetes

“…ing (41,42). Owing to their ability to bind complement regulators, it was hypothesized that CspA proteins of B. afzelii and B. spielmanii also was responsible for serum resistance (12,15,56), but unambiguous proof-of-principle studies with viable spirochetes producing individual CspA orthologs are still lacking.…”

“…The role of CspA in facilitating complement resistance has recently been demonstrated using an avirulent and a virulent cspAdeficient mutant of B. burgdorferi B31 (41,42). Lack of CspA results in a strong susceptibility to complement-mediated killing accompanied with a simultaneous increase of activated complement components on the surface of CspA-deficient cells.…”

“…Mutants lacking CspA are highly susceptible to complement-mediated killing, and complementation with the cspA gene of B. burgdorferi completely restores serum resistance (41,42). In addition to the aspects already addressed above, CspA interacts with late complement components and thereby inhibits assembly of the pore-forming terminal complement complex (43).…”

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

“…The CFH/CFHR1-binding proteins include ErpP, ErpC, and ErpA, i.e., members of the OspEF (Erp) protein family, OspE, and the p21 protein (1,16,18,21,25,40,51,54). Expression of CspA or CspZ correlates with serum resistance in vitro, and heterologous expression of either CspA or CspZ converts a serum-susceptible into a serum-resistant phenotype, thus demonstrating an important role for each of the two molecules in evasion of complement-mediated killing (7,15,23,52). The unique association of B. lusitaniae with lizards and its somewhat weak pathogenic potential for humans may suggest particular properties of this genospecies toward serum complement.…”

Proteomic-Based Approach To Gain Insight into Reprogramming of THP-1 Cells Exposed to Leishmania donovani over an Early Temporal Window

“…The membranes were incubated with primary antibodies against hnRNP K (R332; Cell Signaling) (1:1,000), mitochondrial antiviral signaling protein (MAVS) (E-3; Santa Cruz Biotechnology) (1:1,000), protein tyrosine phosphatase nonreceptor type 6 (PTPN6)/Src homology region 2 domain-containing phosphatase 1 (SHP-1) (C-19; Santa Cruz Biotechnology) (1:1,000), the 78-kDa glucose-regulated protein (GRP78) (A-10; Santa Cruz Biotechnology) (1:1,000), high-mobility-group protein I (HMG-I) (EPR7839; Abcam) (1:10,000), histone H4 (L64C1; Cell Signal-ing) (1:1,000), and beta-tubulin (Thermo Scientific, USA) (1:5,000) prepared in PBST at room temperature for 1 h. The blots were subsequently incubated with the secondary antibody conjugated to horseradish peroxidase in PBST for 1 h at room temperature. Protein bands were observed on X-ray film by using an enhanced chemiluminescence kit (G Biosciences, USA) (25).…”