IMMUNOELECTRON MICROSCOPY REVEALS THAT THE EXCITOTOXIN QUINOLINATE ISASSOCIATED WITH THE PLASMA-MEMBRANE IN HUMAN PERIPHERAL-BLOOD MONOCYTES MACROPHAGES/

Quinolinate (QUIN), a tryptophan-derived excitotoxin, was localized ul trastructurally in human peripheral blood monocytes/macrophages (M emp ty set) by immune-electron microscopy. A combined carbodiimide/glutara ldehyde/paraformaldehyde-based fixation procedure was developed for op timal retention of QUIN in the cell as well as minimal loss of ultrast ructure; a silver-enhanced colloidal gold detection system was used fo r electron-microscopic analysis. Gold particles representing QUIN immu noreactivity were associated with the inner side of the plasma membran e in normal M empty set. The number of gold particles increased signif icantly when QUIN levels were elevated by treatment with its precursor kynurenine, but location of the gold particles remained essentially t he same under this condition. Treatment with interferon-gamma increase d the number of Golgi bodies, vacuoles and pseudopodia, reflecting the activated state of the cell. Significantly increased numbers of gold particles representing QUIN were detectable in approximately the same location as in the case of kynurenine treatment. Combined treatment wi th kynurenine and interferon-gamma maximally increased the number of g old particles at the periphery of the cell. The pseudopodia were inten sely stained with gold particles, while they were not detectable in th e inner part of the cytoplasm or in any other organelle even under thi s activated condition. The significance of the specific location of QU IN revealed in the present study and its relation to the release and s ubsequent actions of QUIN are discussed.