Variation in interferon-gamma responses to Coxiella burnetii antigens with lymphocytes from vaccinated or naturally infected subjects.

Previous work in our laboratory has shown that lymphocytes from persons vaccinated with a formalin-inactivated Phase I Q fever vaccine (Q-Vax CSL Ltd) show a mitogenic response to Coxiella burnetii antigens. The mitogenic response is the sum of that from various subsets of CD4+, T helper cells, CD8+ T cells and probably B cells. It does not distinguish between T helper cell responses leading to formation of interferon-gamma (IFN-gamma)--a cytokine responsible for clearing intracellular infection with C. burnetii organisms--and responses of other T cell subsets which may produce disease-enhancing cytokines. The present study analyses (i) the capacity of Q-Vax to induce T cell sensitization which leads to IFN-gamma responses on antigen stimulation, and (ii) the immunomodulatory, (down-regulatory) effects of the Phase I lipopolysaccharide (LPS) of the organism, which interacts with monocyte/macrophages to limit IL-2 production and production of IFN-gamma by sensitized T lymphocytes.