Francisella tularensis causes disease (tularemia) in a large number of mammals, 
including man. We previously demonstrated enhanced efficacy of conventional 
antibiotic therapy for tularemia by postexposure passive transfer of immune sera 
developed against a F. tularensis LVS membrane protein fraction (MPF). However, 
the protein composition of this immunogenic fraction was not defined. Proteomic 
approaches were applied to define the protein composition and identify the 
immunogens of MPF. MPF consisted of at least 299 proteins and 2-D Western blot 
analyses using sera from MPF-immunized and F. tularensis LVS-vaccinated mice 
coupled to liquid chromatography-tandem mass spectrometry identified 24 
immunoreactive protein spots containing 45 proteins. A reverse vaccinology 
approach that applied labeling of F. tularensis LVS surface proteins and 
bioinformatics was used to reduce the complexity of potential target immunogens. 
Bioinformatics analyses of the immunoreactive proteins reduced the number of 
immunogen targets to 32. Direct surface labeling of F. tularensis LVS resulted 
in the identification of 31 surface proteins. However, only 13 of these were 
reactive with MPF and/or F. tularensis LVS immune sera. Collectively, this use 
of orthogonal proteomic approaches reduced the complexity of potential 
immunogens in MPF by 96% and allowed for prioritization of target immunogens for 
antibody-based immunotherapies against tularemia.