Chlamydia pneumoniae is an intracellular pathogen that grows inside a vacuole, referred to as an inclusion. C. pneumoniae possess a type III secretion system (TTSS), which allows them to secrete effector molecules into the inclusion membrane and to the host cell cytosol. Proteins such as chlamydial outer protein N (CopN) that associate with the inclusion membrane are potential targets for the host's MHC-dependent antigen presentation, thereby representing ideal antigen candidates for T cell-based vaccination. The results of this study showed that intranasal immunization of BALB/c mice with heat-aggregated CopN protein and an Escherichia coli heat-labile toxin (LT) induced a strong immune response, detected as antigen-specific antibody production, lymphocyte proliferation and IFN-gamma production. Furthermore, the immunization induced statistically significant protection against intranasal C. pneumoniae challenge, the level of which correlated with the magnitude of CopN-specific lymphocyte proliferation. Both heat-aggregation of the antigen and the presence of LT adjuvant were required for maximal protective effect.