title: Induction of tryptophan catabolism is the mechanism for gamma-interferon-mediated inhibition of intracellular Chlamydia psittaci replication in T24 cells.
abstract: Human uroepithelial (T24) cells were incubated for 24 h in the presence of various concentrations of human recombinant gamma interferon (Hu-rIFN-gamma) and then infected with the 6BC strain of Chlamydia psittaci. This resulted in a reduction of intracellular chlamydial inclusion development in proportion to the concentration of Hu-rIFN-gamma present when Giemsa-stained cells were examined by light microscopy 24 h after infection. When tryptophan was added to Hu-rIFN-gamma-treated cells just after infection, reversal of the Hu-rIFN-gamma-mediated inhibition occurred in proportion to the concentration of tryptophan added. Addition of either isoleucine or lysine did not result in reversal of the antichlamydial state. Transport of L-[3H]tryptophan into acid-soluble intracellular pools was found to be greatly enhanced in Hu-rIFN-gamma-treated T24 cells compared with the rates measured for untreated cells. Transport of [3H]leucine was not increased in treated cells. Cells treated with Hu-rIFN-gamma also degraded L-[3H]tryptophan to catabolites that cochromatographed with N-formylkynurenine and kynurenine as measured by high-performance liquid chromatography. We conclude that Hu-rIFN-gamma-mediated inhibition of intracellular C. psittaci replication in T24 cells occurs by depletion of the essential amino acid tryptophan, most likely via the induction of indoleamine-2,3-dioxygenase, the initial enzyme of tryptophan catabolism.
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D002691:Chlamydophila psittaci / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D007737:Kynurenine / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D007737:Kynurenine; D007371:Interferon-gamma; D014364:Tryptophan