Toxoplasma gondii triggers secretion of interleukin-12 but low level of interleukin-10 from the THP-1 human monocytic cell line.

Previous studies using both in vitro and in vivo mouse models have demonstrated that a subtle balance between pro- and anti-inflammatory cytokines, among which interleukin-12 (IL-12) and interleukin-10 (IL-10), respectively is crucial to control Toxoplasma infection. However, the few studies performed with human cell lines highlighted important host-related differences in the immune response to Toxoplasma gondii. The goal of our work was thus to study the production of both IL-12 and IL-10 by the THP-1 human monocytic cell line in response to Toxoplasma. We demonstrated that infection by live parasites (RH strain) triggers secretion of IL-12, but low level of IL-10. IL-12 secretion appeared within 8 h, up to 48 h. We also showed that infection by live parasites is not mandatory since heat-killed parasites, crude tachyzoite lysate as well as excreted/secreted antigens induced significant, yet reduced production of IL-12.