Recombinant L7/L12 Ribosomal Protein and Gamma-irradiated Brucella Abortus Induce a T-helper 1 Subset Response from Murine CD4+ T Cells

Immunity to Brucella abortus crucially depends on antigen (Ag)-specific T-cell mediated activation of macrophages, which are the major effectors of cell-mediated killing of this organism. Ribosomal preparations have been used as vaccines against several pathogens, including B. abortus, conferring a high degree of protection. In the present study, we have examined the pattern of T-helper (Th) cell response from infected BALB/c mice after in vitro stimulation with recombinant (r) L7/L12 ribosomal protein or gamma-irradiated B. abortus. In addition to Ag-specific proliferation, CD4+ T cells were tested for interleukin-2 (IL-2), IL-4 and interferon-gamma (IFN-gamma) mRNA expression and secretion. Detection of cytokine transcripts and secreted cytokines was performed using reverse transcriptase (RT)-polymerase chain reaction (PCR) and specific ELISA assays. Primed CD4+ T cells proliferated to the recombinant protein or whole B. abortus. The functional cytokine profile of the proliferating cells was typical of a Th1 cell phenotype, as we detected transcripts for IL-2 and IFN-gamma but not IL-4. Among the cytokines analysed, only IFN-gamma produced in the Th cell culture supernatants was detected by ELISA when bacteria or recombinant protein were used. Thus, rL7/L12 ribosomal protein and gamma-irradiated B. abortus preferentially stimulated IFN-gamma-producing Th1 cells after in vitro stimulation. The results of this study provide for the first time an explanation of why ribosomal vaccines may protect against intracellular infections, and an experimental basis for identifying polypeptides from a pathogen which stimulates the desired cytokine profile and Th cell response crucial for the design of genetically engineered candidate vaccines.