Chlamydia psittaci is the pathogen of
psittacosis, and it has emerged as a significant public health threat. Because most
infections are easily overlooked, a
vaccine is recognized as the best
solution to control the spread of C. psittaci. Our previous study showed that Pgp3
protein is efficacious as a
subunit vaccine while not the best candidate due to the negative effects. Thus, in this study, we tested the ability of a tandem
epitope vaccine candidate designated SP based on Pgp3-dominant
epitopes to induce protective immunity against pulmonary chlamydial
infection. BALB/c mice were intraperitoneally inoculated with multiepitope
peptide antigens followed by intranasal
infection with C. psittaci. We found that the multiepitope
peptide antigens induced strong humoral and cellular immune responses with high Th1-related (IFN-γ and IL-2) and proinflammatory (IL-6)
cytokine levels. Meanwhile, the pathogen burden and inflammatory infiltration were significantly reduced in lungs of SP-immunized mice after chlamydial challenge. In addition, the IFN-γ and
IL-6 secretion levels in the infected lungs were substantially reduced. Overall, our findings demonstrate that the
peptide vaccine SP plays a significant role with good immunogenicity and protective efficacy against C. psittaci lung
infection in BALB/c mice, providing important insights towards understanding the potential of
peptide vaccines as new
vaccine antigens for inducing protective immunity against chlamydial
infection.