Expression of the kynurenine enzymes in macrophages and microglial cells: regulation by immune modulators

The regulation of the expression of indoleamine 2,3-dioxygenase (IDO) was studied in cloned murine macrophages (MT2) and microglial (N11) cells. Both cell lines express IDO and inducible nitric oxide synthase activity after interferon-gamma (IFN-gamma) stimulation. The regulation of IDO expression appears to differ in the two cell lines. Nitric oxide (NO) production negatively modulates the expression of IDO activity in IFN-gamma-primed macrophages, thereby indicating a cross-talk between the kynurenine and nitridergic pathways in these cells. Conversely, this down-regulation of IDO activity by NO does not occur in microglial cells. A differential regulation of IDO expression in the two cell lines was also observed with LPS and picolinic acid. Together with previous findings, these results indicate the existence of marked differences in the regulation of the expression of the kynurenine pathway enzymes between macrophages and microglial cells.