Expression of the kynurenine pathway enzymes in human microglia and macrophages

Adv Exp Med Biol. 2003;527:105-12. doi: 10.1007/978-1-4615-0135-0_12.


There is good evidence that the kynurenine pathway (KP) and one of its products, quinolinic acid (QUIN) play a role in the pathogenesis of neurological diseases. Monocytic cells are known to be the major producers of QUIN. However, macrophages have the ability to produce approximately 20 to 30-fold more QUIN than microglia. The molecular origin of this difference has not been clarified yet. Using unstimulated and IFN-gamma-stimulated cultures of human fcetal microglia and adult macrophages, we assayed mRNA expression of 8 key enzymes of the KP using RT-PCR and QUIN production using GC-MS. We found that after stimulation with IFN-gamma microglia produced de novo 20-fold less QUIN than macrophages. This quantitative difference in the ability to produce QUIN appears to be associated with a lower expression of 3 important enzymes of the KP in microglia: indoleamine 2,3-dioxygenase (IDO), kynureninase (KYNase) and kynurenine hydroxylase (KYN(OH)ase). These results suggest that activated infiltrating macrophages are the most potent QUIN producers during brain inflammatory diseases with playing a lesser role.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cells, Cultured
  • Gene Expression
  • Humans
  • Interferon-gamma / pharmacology
  • Kynurenine / metabolism*
  • Macrophages / drug effects
  • Macrophages / enzymology
  • Macrophages / metabolism*
  • Microglia / drug effects
  • Microglia / enzymology
  • Microglia / metabolism*
  • Quinolinic Acid / metabolism
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Recombinant Proteins
  • Transaminases / genetics


  • RNA, Messenger
  • Recombinant Proteins
  • Kynurenine
  • Interferon-gamma
  • Transaminases
  • kynurenine-oxoglutarate transaminase
  • Quinolinic Acid