CONICET | Buscador de Institutos y Recursos Humanos

The enzyme lumazine synthase from Brucella spp. (BLS) is a highly immunogenic protein that folds as a stable dimer of pentamers. It is possible to insert foreign peptides and proteins at its ten-amino acid termini without disrupting its general folding, and these chimeras are very efficient to elicit systemic and oral immunity without adjuvants, which are commonly needed in the formulation of subunit-based vaccines. We showed that BLS stimulates bone marrow dendritic cells from mice in vitro to up-regulate the levels of costimulatory molecules (CD40, CD80, and CD86) and major histocompatibility class II Ag. Furthermore, the mRNA levels of several chemokines are increased, and proinflammatory cytokine secretion is induced upon exposure to BLS. In vivo, BLS increases the number of dendritic cells and their expression of CD62L in the draining lymph nodes of immunized mice. All of the observed effects are dependent on TLR4. An in vivo cytotoxicity assay showed that immunization with a BLS chimera displaying 10 copies of ovalbumin peptide 257-264 (OVAp) induces a strong OVAp-specific effector CTL response even in the absence of adjuvant and that is dependent on TLR4. To test the ability of BLS to induce the cross-priming of CD8+ cells, transgenic CD8+ cells specific for OVAp were adoptively transferred into normal mice. After 20 h, BLS-OVAp immunization induces the proliferation of OVAp-specific CD8+ lymphocytes and increases the percentage of OVAp-specific CD8+ cells expressing CD69. After 5 days, the percentage of OVAp-specific CD8+ cells expressing high levels of CD44 increases in BLS-OVAp-immunized mice. This cell subpopulation shows a decreased expression of IL-7Rα, indicating that BLS-OVAp induces the generation of CD8+ effector cells. Unlike other subunit-based vaccines, BLS and BLS chimeras induce rapid activation of dendritic cells, CTLs and a specific cytotoxic response, making this polymeric protein an ideal antigen carrier for vaccine development.