Borrelia burgdorferi vesicle production occurs via a mechanism independent of immunoglobulin M involvement.

Abstract

Borrelia burgdorferi produces extracellular vesicles containing various borrelial protein antigens when propagated in vitro in culture media. Commonly observed components of borrelial vesicle preparations are borrelial surface antigens, bovine serum albumin, and the heavy chains of rabbit immunoglobulin G and immunoglobulin M. This study employed ultracentrifugation to harvest borrelial vesicles and analyzed these preparations by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western immunoblotting. We demonstrated that the rabbit mu heavy-chain band observed was devoid of OspA or at most levels below those detectable by immunoblot. We also demonstrated the recovery of borrelial vesicles at relative centrifugal forces as low as 25,000 x g, compared with the force of > 200,000 x g normally employed. Further, the mu heavy-chain band was recovered from uninoculated growth media processed at 25,000 x g, suggesting that it behaves as a particle rather than as a soluble molecule under these conditions. Lastly, vesicles were demonstrated to be present in preparations harvested from growth media supplemented with fetal calf serum, suggesting that vesicle production by B. burgdorferi can occur in the absence of immunoglobulins.