Inhibition of Borrelia burgdorferi-Tick Interactions In Vivo by Outer Surface Protein A Antibody

Abstract

Borrelia burgdorferi outer surface protein (Osp) A is preferentially expressed by spirochetes in the Ixodes scapularis gut and facilitates pathogen-vector adherence in vitro. Here we examined B. burgdorferi-tick interactions in vivo by using Abs directed against OspA from each of the three major B. burgdorferi sensu lato genospecies: B. burgdorferi sensu stricto, Borrelia afzelii, and Borrelia garinii. Abs directed against B. burgdorferi sensu stricto (isolate N40) destroy the spirochete and can protect mice from infection. In contrast, antisera raised against OspA from B. afzelii (isolate ACA-1) and B. garinii (isolate ZQ-1) bind to B. burgdorferi N40 but are not borreliacidal against the N40 isolate. Our present studies assess whether these selected OspA Abs interfere with B. burgdorferi-tick attachment in a murine model of Lyme disease with I. scapularis. We examined engorged ticks that had fed on B. burgdorferi N40-infected scid mice previously treated with OspA (N40, ACA-1, ZQ-1, or mAb C3.78) or control Abs. OspA-N40 antisera or mAb C3.78 destroyed B. burgdorferi N40 within the engorged ticks. In contrast, treatment of mice with OspA-ACA-1 and OspA-ZQ-1 antisera did not kill B. burgdorferi N40 within the ticks but did effectively interfere with B. burgdorferi-I. scapularis adherence, thereby preventing efficient colonization of the vector. These studies show that nonborreliacidal OspA Abs can inhibit B. burgdorferi attachment to the tick gut, highlighting the importance of OspA in spirochete-arthropod interactions in vivo.

OspC facilitates Borrelia burgdorferi invasion of Ixodes scapularis salivary glands

“…In the vector-host transmission cycle, the spirochetes alter their surface structure inside the engorging tick (16,32). B. burgdorferi upregulates ospA during entry into ticks, and this protein contributes to the colonization of spirochetes within the vector gut (12,20). B. burgdorferi, in contrast, does not produce abundant OspC in the gut of an unfed tick (11).…”

“…In selected wells, primary Ab was omitted to measure nonspecific binding. Binding of OspC F(ab) 2 fragments to the surface of B. burgdorferi was performed as described (20) with the following modifications. A volume of 5 µl of spirochetes (10 9 /ml) in PBS was spotted on silylated glass slides, allowed to dry on slides, and incubated for 30 minutes in PBS supplemented with 0.05% Tween-20 and 5% normal goat serum (PST) at room temperature.…”

“…F(ab) 2 fragments were tested for their bactericidal activity against B. burgdorferi N40 by dark-field microscopy as described (20). Briefly, spirochetes (5 × 10 6 /ml) were incubated in BSK-H medium (Sigma-Aldrich, St. Louis, Missouri, USA) supplemented with purified F(ab) 2 fragments (50 µg/ml) for 24-48 hours at 33°C.…”

“…Organs from nymphal ticks were prepared for microscopy as described previously (20). Salivary glands or gut were dissected, washed three times in PBS, placed on silylated glass slides, allowed to dry, and fixed with acetone for 5 minutes.…”

Disruption of Ixodes scapularis anticoagulation by using RNA interference

“…Salivary glands of mock-injected and experimental ticks (10-12 ticks per group, n ϭ 4 experiments) were dissected in PBS, placed on sialylated slides (PGC Scientific, Gaithersburg, MD), washed in PBS, and fixed in acetone (10 min at 4°C) as described (25). Salivary gland samples were blocked in PBS͞10% FCS͞0.5% Tween 20 before antibody incubations.…”