Human macrophages degrade tryptophan upon induction by interferon-gamma

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Tryptophan metabolism is crucial for immune cell function.
• Interferons and T-cell activation influence immune responses.
• Kynurenine pathway metabolites are implicated in immune regulation.

Purpose of the Study:

• To investigate the effect of interferon-gamma, interferon-alpha, and phytohemagglutinin on tryptophan metabolism in human immune cells.
• To identify the specific cell types involved in tryptophan degradation.
• To elucidate the role of T-cells and macrophages in interferon-induced tryptophan metabolism.

Main Methods:

• Human peripheral blood mononuclear cells (PBMCs), monocytes-macrophages, and T-cells were stimulated with recombinant interferons and phytohemagglutinin.
• Culture supernatants were analyzed using high-performance liquid chromatography (HPLC).
• Measurements included tryptophan, kynurenine, 3-hydroxyanthranilic acid, anthranilic acid, and neopterin.

Main Results:

• Stimulation of PBMCs with interferon-gamma, interferon-alpha, or phytohemagglutinin decreased tryptophan and increased kynurenine, 3-hydroxyanthranilic acid, anthranilic acid, and neopterin.
• Monocytes-macrophages, but not T-cells, degraded tryptophan in response to interferon-gamma in a dose-dependent manner.
• Phytohemagglutinin-stimulated T-cells released interferon-gamma, which induced macrophages to degrade tryptophan, correlating with neopterin appearance.

Conclusions:

• Interferon-gamma is a key mediator of tryptophan degradation by macrophages.
• Phytohemagglutinin activates T-cells to produce interferon-gamma, thereby modulating macrophage tryptophan metabolism.
• Neopterin levels serve as a reliable marker for interferon-induced tryptophan degradation in immune cells.