Interleukin-12 in human boutonneuse fever caused by Rickettsia conorii

Interleukin (IL)-12 contributes to the resistance against a number of intra cellular pathogens. We examined the potential biological role of IL-12 by s tudying peripheral blood mononuclear cells (PBMC), its production and its e ffect on cytokine synthesis in 20 Sicilian patients with boutonneuse fever (BF) caused by Rickettsia conorii. Data indicate that PBMC from acute BF pa tients were able to produce IL-12 in response to in vitro stimulation with rickettsial antigen (Ag): this production was higher than that detected in healed patients. Monocytes were the main source of IL-12 by PBMC from BF pa tients. IL-12 secretion by in vitro Ag-stimulated PBMC from BF patients was potentiated by recombinant interferon gamma (IFN-gamma) or anti-IL-10 mono clonal antibodies (MoAbs). Furthermore, the treatment with anti-IL-12 MoAbs reduced the IFN-gamma synthesis. These results indicate that treatment of PBMC from acute BF patients with IL-12 shifted the response toward a Th1-ty pe cytokine response. Furthermore, IL-12 and IFN-gamma are interdependent a nd they may be associated with the immunity against rickettsias.