Facing a bacterial pathogen that may consist of thousands of proteins, the question of how CD4+ T cells selectively target a set of pathogen-derived peptide antigens to confer effective immunity is critical, yet remains largely unanswered. Salmonella enterica is a highly significant bacterial pathogen with a wide host range. In both humans and murine models of the infection, CD4+ T cells play a critical role in host immunity, making it an ideal infection model for studying anti-bacterial CD4+ T cell responses. We hypothesise that effective immunity to Salmonella depends on concurrent targeting of multiple Salmonella-derived antigens by CD4+ T cells, with each antigen making an incremental contribution to the overall immune response. This means that the best vaccine strategy would most likely involve multiple antigenic targets. To demonstrate this, we employed a global and unbiased approach to identify Salmonella-derived, MHC-II-bound peptides from Salmonella-infected dendritic cells using affinity purification and LC-MS/MS. We were then able to validate a collection of novel and immunogenic CD4+ T cell epitopes, mostly representing previously unrecognised vaccine candidates. These novel epitopes were shown to induce distinct types of polyfunctional cytokine responses in the host, indicating a direct role for antigens in shaping the responses and microenvironment of activated CD4+ T cells. Using mice vaccinated with live-attenuated Salmonella strains, we observed that the post-vaccination level of antigen-specific CD4+ T cells is correlated with subsequent protection efficacy against virulent Salmonella infection, suggesting a functional role for these antigen-specific CD4+ T cells. On the other hand, analysis of Salmonella proteins with immunogenic epitopes indicates that antigens abundance most likely plays an important role in determining immunogenicity. With a collection of immunogenic epitopes known, ongoing work aims to formulate a protein-based vaccine that confers protective immunity against virulent Salmonella infection. This will not only help us to discover novel antigens for making vaccines against Salmonella, but also to uncover key features that distinguish protective CD4+ T cell epitopes from non-protective ones. We envisage that this work will provide vital information on how CD4+ T cell select antigens from a complex bacterial pathogen, and bears profound implications for dissecting polyclonal immunity in infection with Salmonella and possibly other bacterial pathogens.