Variable progressive behavior of Klebsiella pneumoniae at different sites of infection.

Klebsiella pneumoniae has persisted for decades as a major global health threat. Although vaccination is widely recognized as the most effective preventive strategy, no vaccine has been commercialized despite more than 50 years of intensive research. While numerous computational studies have screened epitopes from over 25 different Klebsiella protein antigens, none have progressed to vaccine development, underscoring the urgent need for innovative approaches to define the immunological signatures of this pathogen. In this study, infections caused by classical K. pneumoniae (cKp) at distinct anatomical sites were experimentally mimicked in an animal model to investigate antigen-specific host immune responses during infection. Humoral immune responses against major protein and polysaccharide antigens were characterized using immunoblotting and quantitative ELISA, while cellular immune activation was evaluated through lymphocyte proliferation assays. The results revealed the site-specific and progressive antigenic expression patterns of K. pneumoniae, reflecting dynamic host-pathogen interactions across different infection models. Notably, immunoglobulin profiling demonstrated strong potential to discriminate both the stage and route of K. pneumoniae infection. These findings underscore the importance of polysaccharide antigens and protein target mapping prior to in silico epitope prediction for vaccine and diagnostic production.