Increased quinolinate immunoreactivity in the peripheral blood monocytes/macrophages from SIV-infected monkeys

Quinolinate (QUIN), a metabolite in the kynurenine pathway of tryptophan degradation and a neurotoxin that is thought to act through the NMDA receptor system, was localized in cultured peripheral blood monocytes/macrophages from SIV-infected monkeys using a recently developed immunohistochemical method. Significant increases in QUIN immunoreactive (IR) cells were detected in all five SIV-infected monkeys examined. Multinucleated giant cells, a hallmark of lentiviral infection, were visible in selected samples. Treatment with the QUIN precursors, tryptophan and kynurenine, increased the number of QUIN-IR cells in both the control and SIV-infected preparations, perhaps by a mass action mechanism. We hypothesize that in SIV-infected monkeys, infiltrating monocytes/macrophages contribute to the high level of brain QUIN and associated neuropathology.