Differential effects of kynurenine and tryptophan treatment on quinolinate immunoreactivity in rat lymphoid and non-lymphoid organs.

Quinolinate is a tryptophan metabolite and an intermediary in nicotinamide adenine dinucleotide (NAD+) synthesis in hepatocytes. Kynurenine is an upstream metabolite in the same biochemical pathway. Under normal physiological conditions, kynurenine is thought to be produced primarily in the liver as an NAD+ precursor. However, during immune stimulation or inflammation, numerous extrahepatic tissues convert systemic tryptophan to kynurenine, and its concentration subsequently rises dramatically in blood. The fate and role of extrahepatic kynurenine are uncertain. In order to begin addressing this question, the present study was performed to determine which cell types can produce quinolinate from either systemic tryptophan or kynurenine. By using highly specific antibodies to protein-coupled quinolinate, we found that intraperitoneal injections of tryptophan led to increased quinolinate immunoreactivity primarily in hepatocytes, with moderate increases in tissue macrophages and splenic follicles. In contrast, intraperitoneal injections of kynurenine did not result in any significant increase in hepatocyte quinolinate immunoreactivity, but rather led to dramatic increases in immunoreactivity in tissue macrophages, splenic white pulp, and thymic medulla. These findings suggest that hepatocytes do not make significant use of extracellular kynurenine for quinolinate or NAD+ synthesis, and that, instead, extrahepatic kynurenine is preferentially metabolized by immune cells throughout the body. The possible significance of the preferential metabolism of kynurenine by immune cells during an immune response is discussed.

Adenovirus-mediated human immunodeficiency virus-1 Nef expression in human monocytes/macrophages and effect of Nef on downmodulation of Fcgamma receptors and expression of monokines.

To characterize the effect of human immunodeficiency virus-1 (HIV-1) nef expression in human monocytes/macrophage (HMO) and U937 on the levels of FcgammaRs, HLA antigens, and monokines, elutriated HMOs and U937 cells were transfected with an adenovirus-mediated Nef expression system. Nef-expressing cells downmodulated FcgammaRI, FcgammaRII, and upregulated HLA class I molecules. Nef-expressing HMOs, treated with lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA), overexpressed tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-10. However, IL-6 was induced by LPS and inhibited by PMA. Additionally, a subpopulation of Nef-expressing HMOs underwent apoptosis. Our data suggest that HIV-1 nef downmodulated FcgammaRs in myeloid cells in a manner similar to that previously reported for its effect on CD4+ in T cells.

Immuno-electron microscopy reveals that the excitotoxin quinolinate is associated with the plasma membrane in human peripheral blood monocytes/macrophages.

Quinolinate (QUIN), a tryptophan-derived excitotoxin, was localized ultrastructurally in human peripheral blood monocytes/macrophages (MO) by immuno-electron microscopy. A combined carbodiimide/glutaraldehyde/paraformaldehyde-based fixation procedure was developed for optimal retention of QUIN in the cell as well as minimal loss of ultrastructure; a silver-enhanced colloidal gold detection system was used for electron-microscopic analysis. Gold particles representing QUIN immunoreactivity were associated with the inner side of the plasma membrane in normal MO. The number of gold particles increased significantly when QUIN levels were elevated by treatment with its precursor kynurenine, but location of the gold particles remained essentially the same under this condition. Treatment with interferon-gamma increased 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 with kynurenine and interferon-gamma maximally increased the number of gold particles at the periphery of the cell. The pseudopodia were intensely stained with gold particles, while they were not detectable in the inner part of the cytoplasm or in any other organelle even under this activated condition. The significance of the specific location of QUIN revealed in the present study and its relation to the release and subsequent actions of QUIN are discussed.

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.

Immunocytochemical localization of the endogenous neuroexcitotoxin quinolinate in human peripheral blood monocytes/macrophages and the effect of human T-cell lymphotropic virus type I infection.

Quinolinate (Quin), a metabolite in the kynurenine pathway of tryptophan degradation and a neurotoxin that appears to act through the N-methyl-D-aspartate receptor system, was localized in cultured human peripheral blood monocytes/macrophages (PBMOs) by using a recently developed immunocytochemical method. Quin immunoreactivity (Quin-IR) was increased in gamma interferon (IFN-gamma)-stimulated monocytes/macrophages (MOs). In addition, the precursors, tryptophan and kynurenine, significantly increased Quin-IR. Infection of MOs by human T-cell lymphotropic virus type I (HTLV-I) in vitro substantially increased both the number of Quin-IR cells and the intensity of Quin-IR. At the peak of the Quin-IR response, about 40% of the cells were Quin-IR positive. In contrast, only about 2-5% of the cells were positive for HTLV-I, as detected by both immunofluorescence for the HTLV-I antigens and PCR techniques for the HTLV-I Tax gene. These results suggest that HTLV-I-induced Quin production in MOs occurs by an indirect mechanism, perhaps via cytokines produced by the infection but not directly by the virus infection per se. The significance of these findings to the neuropathology of HTLV-I infection is discussed.

Induction of alpha interferon by human immunodeficiency virus type 1 in human monocyte-macrophage cultures.

The induction of interferon (IFN) by human immunodeficiency virus type 1 (HIV-1) in primary, nonstimulated monocyte-macrophage cultures was studied. HIV-1 infection, as confirmed by p24 antigen levels in the cell supernatant, led to the production of alpha interferon (IFN-alpha) over 7 to 21 days following infection. In two of seven experiments, the IFN detected was acid labile. Coupled reverse transcription-polymerase chain reaction analysis confirmed the induction of IFN-alpha mRNA in cells of HIV-1-infected cultures.

Capping and internalization of a monoclonal antibody-surface antigen complex: a possible mode of interaction of monoclonal antibodies and tumor cells.

Our results demonstrate that upon incubation of 125I-3G5 (a monoclonal IgM against a membrane ganglioside antigen on RINm5F cells) with rat insulinoma RINm5F cell monolayers at 37 degrees C, the IgM is rapidly internalized. Cell-bound radioactivity, detectable within 10 to 15 minutes, reaches a peak at 4 hours. By 24 hours the intracellular radioactivity has decreased to about 37.5% of the 4-hour value, accompanied by an increase in free 125I in the incubation medium. The incubation of 125I-3G5 with RINm5F cell monolayers at 4 degrees C shows that this series of events is inhibited by low temperature. Microautoradiography confirms these events indicating the presence of radiolabeled antibody on the plasma membrane as well as distinct capping processes and diffuse radioactive deposits within the cells as early as 5 to 10 minutes after initiating incubation at 37 degrees C. Electron microscopy autoradiography provides a detailed demonstration of the capping phenomenon and of endocytic vacuoles, followed at later times by the distribution of radioactive deposits throughout the cell. This model constituted by the capping of the 125I-3G5-ganglioside complex on rat insulinoma RINm5F cells may be useful in elucidating a possible mode of interaction of monoclonal antibodies and tumor cells.

Synthesis and biological activity of the intercalating agent 3-acetamido-5-[123/125I]iodo-6-aminoacridine.

3-Acetamido-5-iodo-6-aminoacridine (3), a derivative of the known intercalating agent proflavine (3,6-diaminoacridine) (1) was synthesized, and no-carrier-added 123I and 125I labeled compounds prepared. Compound 3 was taken up by live cells and localized in the nucleus. The intracellular concentration of [125I]3 was 7-fold greater in human prostate carcinoma (PC-3) cells than in normal Chinese hamster lung fibroblast (V-79) cells.

Monoclonal antibody internalization by tumor cells: an experimental model for potential radioimmunotherapy applications.

The monoclonal IgM 3G5, which reacts with the surface membranes of rat insulinoma cells RINm5F, was purified by HPLC and labeled with 125I using Protag-125; bovine IgG (bIgG) was similarly radiolabeled, and used as a control. 125I-3G5 was incubated with RINm5F cells either at 4 degrees C or at 37 degrees C. 125I-3G5 bound onto RINm5F cells growing in Petri dishes remained approx. constant over 44 h when incubated at 4 degrees C, whereas at 37 degrees C radioactivity was released back in the medium starting at 3 h (plateau at approx. 20 h). At the end of incubation at 37 degrees C, activity in the medium included a high percentage of free 125I (15.69 vs 2.62% for bIgG, and 1% for 3G5 at 4 degrees C). In a cell suspension experiment, cell-bound 125I-3G5 also remained constant over a 24 h incubation at 4 degrees C, whereas at 37 degrees C it decreased to 37.5% of its initial value (64.1% at 4 h). Concomitant microautoradiography showed diffuse radioactive deposits within the RINm5F cells following incubation with 125I-3G5 (but not 125I-bIgG) at 37 degrees C. These results indicate that 3G5-IgM reacts with a surface antigen on the RINm5F cells, but is rapidly internalized by the cells: within the cells, this antibody undergoes some metabolic processing which results in the release of free 125I outside the cells.

Dengue 4 virus monoclonal antibodies identify epitopes that mediate immune infection enhancement of dengue 2 viruses.

Nineteen monoclonal antibodies produced to dengue type 4 virus (DEN-4) strain 4328-S were tested for their ability to mediate antibody-dependent infection enhancement (ADE) with seven DEN-2 strains in P-388D1 mouse macrophage-like cells. In this first study of the distribution of enhancing epitopes on multiple DEN-2 strains reacted with monoclonal antibodies to a different serotype (DEN-4), DEN-4 monospecific antibodies produced ADE with DEN-2 viruses, indicating the presence of DEN-4-like determinants on DEN-2 viruses. Analysis differentiated at least one and possibly more DEN-2 strain subgroups, one of which (isolates AHF-110 and AHF-191) was previously identified by DEN-2 monoclonal antibody analysis. The study demonstrates the heterogeneous distribution of dengue complex and DEN-4 epitopes on DEN-2 strains. Monoclonal antibodies are valuable tools for study of the biology of ADE and its relation to dengue shock syndrome.

Heterogeneity of infection enhancement of dengue 2 strains by monoclonal antibodies.

Seven dengue (DEN) 2 virus strains were studied for antibody-dependent enhancement (ADE) of infection in P388D1 mouse macrophage-like cells by using a panel of five DEN 2 monoclonal antibodies. DEN 2 strains were of diverse temporal, geographic, and disease origins. By hemagglutination inhibition and a plaque-reduction neutralization test in LLC-MK2 cells, two of the monoclonal antibodies were type specific and three were flavivirus group reactive. In LLC-MK2 cells, the seven DEN 2 viruses each were neutralized by all five monoclonal antibodies. In P388D1 cells, two DEN 2 strains were enhanced by only three monoclonal antibodies, two by four antibodies, and three by all five antibodies, demonstrating that in some instances enhancement is epitope related and not a concentration-dependent function of virus-antibody interactions. However, ADE did not segregate with determinants exhibiting either the flavivirus group or the dengue type specificity. The presence or absence of enhancement determinants on DEN 2 strains did not correlate with the geographic origin of virus or the severity of disease yielding the strain. The heterogeneous distribution of enhancement determinants may provide a valence mechanism contributing to a multiple increase of infection enhancement in macrophages.

Treatment of intracranial dengue virus infections in mice with a lipophilic derivative of ribavirin.

Rimantadine, ribavirin, and 6-mercapto-9-(tetrahydro-2-furyl)purine, administered intraperitoneally every 8 h for 7 days starting minutes after virus challenge, had no effect on survival and mean survival time of BALB/c mice inoculated intracranially with dengue virus type 2. In contrast, intraperitoneal treatment with ribavirin 2',3',5'-triacetate, a lipophilic analog of ribavirin, effected significant increases in both mean survival time and survival rate, suggesting that ribavirin 2',3',5'-triacetate may be superior to rabavirin for treatment of viral diseases of the brain.