Infection of epithelial and dendritic cells by Chlamydia trachomatis results in IL-18 and IL-12 production, leading to interferon-gamma production by human natural killer cells.

Control of infection by Chlamydia trachomatis usually requires the production of interferon-gamma. Whilst this can be produced by CD4+ and CD8+ T lymphocytes, natural killer (NK) cells are another important source of this cytokine, and are known to be recruited early to the infected genital tract. We show that both IL-12 and IL-18, which synergise to stimulate NK cells to produce interferon-gamma, are produced following the infection of dendritic cells and epithelial cells respectively, since supernatants from infected cells could substitute for recombinant cytokines. These results suggest that conditions, which lead to NK cell production of interferon-gamma will be present at the site of infection, where epithelial cells are the primary targets of infection and dendritic cells within the epithelium can also access the bacterium.