Study of receptor-mediated neurotoxins released by HIV-1-infected mononuclear phagocytes found in human brain

Adenovirus-Mediated Human Immunodeficiency Virus-1 Nef Expression in Human Monocytes/Macrophages and Effect of Nef on Downmodulation of Fcγ Receptors and Expression of Monokines

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

Adenovirus-Mediated Human Immunodeficiency Virus-1 Nef Expression in Human Monocytes/Macrophages and Effect of Nef on Downmodulation of Fcγ Receptors and Expression of Monokines

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

Axonal sprouting in hippocampus of cats infected with feline immunodeficiency virus (FIV)

Neurologic dysfunction and neuropathology are common findings in patients infected with HIV and in cats infected with feline immunodeficiency virus (FIV). The pathogenesis of lentivirus-associated alterations in the central nervous system (CNS) is multifactorial. Because seizures, alterations in memory, and behavioral changes are clinical manifestations in adults and children infected with HIV, we explored the possibility that changes in neuronal structure may occur in the hippocampus. To do this, we examined the dentate gyrus of FIV-infected cats, an animal model of HIV infection. Neuropathologic findings included gliosis within the hilus of the dentate gyrus and granule cell axonal sprouting. Using the Timm's method, which labels axons of dentate gyrus granule cells, abnormally high amounts of staining were observed in the inner one third of the molecular layer in 45% of FIV-infected cats (n = 11) and in none of the controls (n = 19). Prominent axonal sprouting was seen in three FIV-infected cats that were infected as kittens, suggesting that younger cats may be more susceptible. Axon reorganization of the dentate granule cells has been hypothesized to underlie complex partial seizure activity in human temporal lobe epilepsy. These results suggest that FIV infection causes granule cell axon reorganization in the hippocampus of cats. A similar neuropathogenetic mechanism may contribute to neurologic dysfunction in HIV-infected patients.

Cortical cell loss in asymptomatic cats experimentally infected with feline immunodeficiency virus

Specific pathogen-free cats experimentally infected with feline immunodeficiency virus (FIV) were used to evaluate the development of central nervous system changes during the asymptomatic stages of viral infection. The brains of asyptomatic cats were examined at postinoculation times ranging from 8 weeks to 3 years for changes in neuron density, glutamate receptor density, and synaptophysin immunoreactivity. At 2-3 years postinoculation a small decrease in neuronal density was found in layers 2-3 and layer 5 of the frontal cortex (-14.4%), parietal cortex (-18.1%), and striatum (-29.5%). The only other indications of pathology within these regions were a mild diffuse astrogliosis, occasional microglial nodules, and the accumulation of satellite cells around selected neurons. An average loss of large neurons of 56-68% was seen in the cortex of four random source cats euthanized with AIDS. These values contrasted with the absence of any significant cell loss in FIV-infected cats 18 weeks after inoculation or FIV-negative controls. The loss of neurons in the asymptomatic cats showed a significant positive correlation with a decrease in the blood CD4:CD8 ratios. Morphometric evaluation of synaptic terminal densities immunocytochemically stained with synaptophysin revealed a significant increase in the asymptomatic cats at 2-3 years postinoculation that correlated negatively with the CD4:CD8 ratios. Random source AIDS cats showed a 34% decrease in synaptophysin-immunoreactive profiles. Glutamate binding in the cortex did not change significantly in the asymptomatic cats (4-7% decline). Thus, experimentally infected specific pathogen-free cats show a loss of cortical neurons similar to what has been observed in postmortem studies of humans infected with HIV. The detection of neuronal loss during the asymptomatic stage of disease and the correlation with the peripheral CD4:CD8 cell ratios indicate that neurodegeneration may progress in parallel with peripheral disease.

Quinolinic acid and lymphocyte subsets in the intrathecal compartment as biomarkers of SIV infection and simian AIDS

Cerebrospinal fluid (CSF) samples were collected from monkeys infected with SIVmac251 (SIV) or HIV-1/SIVmac chimeric viruses (SHIV(HXBc2) and SHIV(89.6P)) to investigate quinolinic acid (QUIN) levels in the intrathecal compartment. CSF levels of QUIN were elevated in the SIV-infected monkeys, especially in animals with end-stage disease, and in those infected with pathogenic SHIV(89.6P), but not after infection with the nonpathogenic construct SHIV(HXBc2). QUIN elevations occurred in association with reduced CD4+ and increased CD8+ lymphocytes, cellular alterations that were more pronounced in CSF than in the blood. These findings support the view that the intrathecal compartment provides a unique window on viral infection, and are in keeping with the a priori prediction that QUIN increases primarily in response to more pathogenic viral strains.