Exploratory Study on Th1 Epitope-Induced Protective Immunity against <i>Coxiella burnetii</i> Infection

<div><p><i>Coxiella burnetii</i> is a Gram-negative bacterium that causes Q fever in humans. In the present study, 131 candidate peptides were selected from the major immunodominant proteins (MIPs) of <i>C. burnetii</i> due to their high-affinity binding capacity for the MHC class II molecule H2 I-A^b based on bioinformatic analyses. Twenty-two of the candidate peptides with distinct MIP epitopes were well recognized by the IFN-γ recall responses of CD4⁺ T cells from mice immunized with parental proteins in an ELISPOT assay. In addition, 7 of the 22 peptides could efficiently induce CD4⁺ T cells from mice immunized with <i>C. burnetii</i> to rapidly proliferate and significantly increase IFN-γ production. Significantly higher levels of IL-2, IL-12p70, IFN-γ, and TNF-α were also detected in serum from mice immunized with a pool of the 7 peptides. Immunization with the pool of 7 peptides, but not the individual peptides, conferred a significant protection against <i>C. burnetii</i> infection in mice, suggesting that these Th1 peptides could work together to efficiently activate CD4⁺ T cells to produce the Th1-type immune response against <i>C. burnetii</i> infection. These observations could contribute to the rational design of molecular vaccines for Q fever.</p>