Anthicha Kunjantarachot, Weiwei Yan, Sean P. McDonough, Siriwan Prapong, Gunjana Theeragool and Yung-Fu Chang
Animal Leptospirosis, caused by Leptospira spp., is one of the most common zoonotic diseases in the US and throughout the world. Commercially available bacterins are only partially efficacious in that they protect against death, but not against disease. Protective immunity to Leptospira spp. require antibodies specific to outer surface proteins and/or adhesins of leptospires. Spirochetes produce membrane blebs or vesicles (OMVs) and OMVs have been shown to be good immunogens. In this study, we characterized leptospiral OMV components by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of and identified that the majority (58.1%) of proteins in the vesicles were cytoplasmic proteins (294 of 506), while 5 were extracellular proteins (0.99%), 11 were outer membrane proteins (2.17%), 14 were periplasmic proteins (2.77%), 48 were cytoplasmic/inner membrane proteins (9.49%) and 134 were unknown or having multiple locations (26.48%). Transmission electron microscopy (TEM) imaging showed OMVs are spherical bodies with a diameter of 50-200 nm. Vesicles were used to vaccinate hamsters. The results indicated that immunization with Leptospira OMVs induced significant protection against lethal challenge revealed by an enhanced humoral immune response, high survival rate and significantly reduced bacterial burden, all of which were reflected in decreased pulmonary, hepatic and renal lesions (p<0.05). To the best of our knowledge, this is the first report showing that OMVs could be used as a novel vaccine formulation to protect hamsters against lethal challenge.