Antibody Response to Lyme Disease Spirochetes in the Context of VlsE-Mediated Immune Evasion

Abstract

Lyme disease (LD), the most prevalent tick-borne illness in North America, is caused by Borrelia burgdorferi. The long-term survival of B. burgdorferi spirochetes in the mammalian host is achieved though VlsE-mediated antigenic variation. It is mathematically predicted that a highly variable surface antigen prolongs bacterial infection sufficiently to exhaust the immune response directed toward invariant surface antigens. If the prediction is correct, it is expected that the antibody response to B. burgdorferi invariant antigens will become nonprotective as B. burgdorferi infection progresses. To test this assumption, changes in the protective efficacy of the immune response to B. burgdorferi surface antigens were monitored via a superinfection model over the course of 70 days. B. burgdorferi-infected mice were subjected to secondary challenge by heterologous B. burgdorferi at different time points postinfection (p.i.). When the infected mice were superinfected with a VlsEdeficient clone (ΔVlsE) at day 28 p.i., the active anti-B. burgdorferi immune response did not prevent ΔVlsE-induced spirochetemia. In contrast, most mice blocked culture-detectable spirochetemia induced by wild-type B. burgdorferi (WT), indicating that VlsE was likely the primary target of the antibody response. As the B. burgdorferi infection further progressed, however, reversed outcomes were observed. At day 70 p.i. the host immune response to non-VlsE antigens became sufficiently potent to clear spirochetemia induced by ΔVlsE and yet failed to prevent WT-induced spirochetemia. To test if any significant changes in the anti-B. burgdorferi antibody repertoire accounted for the observed outcomes, global profiles of antibody specificities were determined. However, comparison of mimotopes revealed no major difference between day 28 and day 70 antibody repertoires.

Identification of Surface Epitopes Associated with Protection against Highly Immune-Evasive VlsE-Expressing Lyme Disease Spirochetes

“…To further characterize the antibody response in the protected and nonprotected animals, an approach that involved RPPDL/NGS was taken. This approach was successfully applied to define the anti-Borrelia antibody repertoires in persistently B. burgdorferi-infected mice (24). Thus, in order to compare the antibody repertoires in the protected and nonprotected mice, four protective serum samples from group 4ϫ mice and three non- a Mice singly immunized with the in vitro-grown ΔVlsE strain were sacrificed at day 28 after wild-type challenge (18).…”

“…Bacterial strains. Previously generated and characterized B. burgdorferi B31-A3/lp25::kan (WT) (78) and B31-A3/lp28-1 Δvls lp25::gent (ΔVlsE clone) (24) clones were used in the present study (Table 8). Borrelia spirochetes were grown in liquid Barbour-Stoenner-Kelly medium (BSK-II) supplemented with 6% rabbit serum (Gemini Bio-Products, CA, USA) and incubated at 35°C under 2% CO 2 .…”

“…A total of 18 male C3H/HeJ (C3H) mice 4 to 6 weeks of age (The Jackson Laboratory, ME, USA) were divided into three groups (6 animals per group), designated groups 1ϫ, 3ϫ, and 4ϫ (Fig. 1), and were immunized with the host-adapted ΔVlsE (ha-ΔVlsE) clone as described previously (24). Briefly, ear pinnae from each SCID mouse were excised as small circular pieces (approximately 2 mm in diameter).…”

“…The second is VlsE-mediated suppression of the host immune response (18,22). Prior data suggest that if VlsE is indeed involved, detectable immunosuppression is only transient and, practically, not sufficient for surface antigens to evade antibodymediated clearance in the long run (23,24). On the other hand, if the VlsE-mediated masking is in place, it is highly unlikely that VlsE molecules entirely shield the surface antigens of B. burgdorferi.…”

Delineating Surface Epitopes of Lyme Disease Pathogen Targeted by Highly Protective Antibodies of New Zealand White Rabbits

“…Three individual serum samples from day 14 and three individual serum samples from day 28 were analyzed via RPPDL/NGS, the approach that was successfully applied to identify antibody repertoires in B. burgdorferi-infected mice (59,63). As a background control, preimmune sera collected from the three NZW rabbits prior to their challenge were pooled in equal volumes and analyzed as a single sample.…”