Antimalarial drug chloroquine counteracts activation of indoleamine (2,3)-dioxygenase activity in human PBMC

Antimalarial chloroquine is also used for the treatment of immune-mediated diseases. The interference of chloroquine with interferon-γ-induced tryptophan breakdown and neopterin production has been investigated in human peripheral blood mononuclear cells (PBMC) in vitro. Micromolar concentrations (2–50 μM) of chloroquine dose-dependently suppressed mitogen-induced tryptophan breakdown in PBMC but not in the myelomonocytic THP-1-Blue cell line, after 48 h of treatment. In stimulated PBMC, neopterin production was super-induced by 10 μM chloroquine, while it was significantly suppressed at a concentration of 50 μM. These anti-inflammatory effects may relate to the therapeutic benefit of chloroquine in inflammatory conditions and may widen the spectrum of its clinical applications.

▸ 2–50 μM chloroquine suppresses mitogen-induced tryptophan breakdown in human PBMCs. ▸ The same effect was not seen in the myelomonocytic THP-1-Blue cell line. ▸ The anti-inflammatory property of chloroquine targets T cells more than monocytes. ▸ This anti-inflammatory effect may explain the drug's therapeutic benefit for malaria. ▸ Chloroquine treatment could be of benefit for other chronic inflammatory conditions.