Two outer membrane lipoproteins from Histophilus somni are immunogenic in rabbits and sheep and induce protection against bacterial challenge in mice.

Histophilus somni is an economically important pathogen of cattle and other ruminants and is considered one of the key components of the bovine respiratory disease (BRD) complex, the leading cause of economic loss in the livestock industry. BRD is a multi-factorial syndrome, in which a triad of agents including bacteria, viruses and predisposing factors or "stressors", combines to induce disease. While vaccines against H. somni have been used for many decades, traditional bacterins have failed to demonstrate effective protection in vaccinated animals. Hence, the BRD complex continues to produce strong adverse effects on the health and wellbeing of stock and feeder cattle. The generation of recombinant proteins may facilitate the development of more effective vaccines against H. somni, which could confer better protection against BRD. In the present work, primers were designed to amplify, clone, express and purify two recombinant lipoproteins from H. somni; p31 (Plp4) and p40 (LppB), which are structural proteins of the outer bacterial membrane. The results presented here demonstrate to our knowledge for the first time, that when formulated, an experimental vaccine enriched with these two recombinant lipoproteins, these generates high antibody titers in rabbits and sheep and exert a protective effect in mice against septicemia induced by H. somni bacterial challenge.