Mononuclear phagocytes (microglia, macrophages, and macrophage-like giant cells) are the principal cellular targets for human immunodeficiency virus-1 (HIV-1) in the central nervous system (CNS). Since HIV-1 does not directly infect neurons, the causes for CNS dysfunction in acquired immunodeficiency syndrome (AIDS) remain uncertain. HIV-1-infected human monocytoid cells, but not infected human lymphoid cells, released toxic agents that destroy chick and rat neurons in culture. These neurotoxins were small, heat-stable, protease-resistant molecules that act by way of N-methyl-D-aspartate receptors. Macrophages and microglia infected with HIV-1 may produce neurologic disease through chronic secretion of neurotoxic factors.

Mononuclear phagocytes infected with human immunodeficiency virus 1 (HIV-1) produce soluble factors that kill neurons in culture. To defne the molecular events that lead to neuron killing, HIV-1 proteins were tested for the ability to trigger release of neurotoxins from human monocytes and lymphocytes. None of the recombinant-derived HIV-1 proteins examined (reverse transcriptase, protease, gag, nef, or gp120) were directly neurotoxic at concentrations from 100 pM to 10 nM. The envelope glycoprotein gp120 did, however, stimulate both isolated human blood monocytes and the monocytoid line THP-1 (but not lymphocytes or the lymphoid cell line 119) to discharge neurotoxic factors. These toxins consisted of heatstable, protease-resistant molecules (<500 Da) that copurified with neurotoxins from HIV-1-infected THP-1 cells and were blocked by antagonists to N-methyl-D-aspartate receptors. Release of neurotoxins through gpl20 stimulation involved monocytoid CD4 receptors because toxin production could be inhibited either by a monoclonal antibody to the CD4-binding region of gpl20 or by soluble CD4 receptors. Alternatively, production of neuron-killing factors could be induced with a peptide from the CD4-binding region of gpl20. These data show that the HIV-1 envelope glycoprotein alone can stimulate neurotoxin release by binding to CD4 receptors of mononuclear phagocytes. Such neurotoxic factors may, in turn, contribute to the central nervous system dysfunction associated with HIV-1 by acting on neurons through N-methyl-D-aspartate receptors.AIDS produces a devastating effect upon the brain and spinal cord with >70% of patients showing loss of memory, paralysis, seizures, sensory deficits, or global dementia (for review, see ref. 1). Human immunodeficiency virus type 1 (HIV-1) has been isolated from the central nervous system (CNS) of AIDS patients and identified in several classes of CNS mononuclear phagocytes-e.g., microglia, macrophages, and multinucleated macrophage-like cells (for review, see ref.2). Although direct viral infection of neurons in brain tissue has not been demonstrated by immunohistology or by in situ hybridization (2), a recent ultrastructural study showed extensive neuronal damage (3). It has been proposed that AIDS-associated neurologic dysfunction stems from either the direct neurotoxicity of HIV proteins such as the envelope glycoprotein gp120 (4, 5) or some indirect mechanism involving HIV-1-infected mononuclear phagocytes (6, 7). We favor the latter hypothesis because we have shown that HIV-1-infected human monocytoid cell lines, but not an infected human lymphoid line, produced a neurotoxic activity (6) that functioned through the N-methyl-D-aspartate (NMDA) type of glutamate receptor. We report here that gpl20, although not directly neurotoxic, can produce neuronal damage by stimulating monocytes to release NMDA receptor-mediated toxins. METHODSCell Culture. Ciliary neurons were prepared from 9-day-old chicken embryos, as described (8), and grown in 1.0 ml of N2 medium/0.4% horse ser...

Although there is growing evidence that neurotoxic molecules produced by HIV-1-infected mononuclear phagocytes damage neurons, the precise mechanisms of neuronal attack remain uncertain. One class of cytotoxin involves neuronal injury mediated via the NMDA receptor. We examined blood monocytes and brain mononuclear cells isolated at autopsy from HIV-1-infected individuals for the ability to release NMDA-like neuron-killing factors. We found that a neurotoxic amine, NTox, was produced by blood monocytes and by brain mononuclear phagocytes infected with retrovirus. In vivo injections of minute quantities of NTox produced selective damage to hippocampal pyramidal neurons. NTox can be extracted directly from brain tissues infected with HIV-1 and showed structural features similar to wasp and spider venoms. In contrast to NTox, HIV-1 infection did not increase the release of the NMDA excitotoxin quinolinic acid (QUIN) from mononuclear cells. Although we found modest elevations of QUIN in the CSF of HIV-1-infected individuals, the increases were likely attributable to entry through damaged blood-brain barrier. Taken together, our data pinpoint NTox, rather than QUIN, as a major NMDA receptor-directed toxin associated with neuro-AIDS.

To determine whether peripheral blood mononuclear cells (PBMCs) contain replicating forms of hepatitis B virus (HBV) DNA and to define which cell subset may be permissive for viral replication, we analyzed the PBMC DNA from 14 carriers positive for hepatitis B surface antigen (HBsAg) by Southern blot hybridization. HBV-related DNA, which was present exclusively in an extrachromosomal state, was found in the PBMCs of all five hepatitis B e antigen (HBeAg)-positive and three of nine HBeAg-negative carriers. Serum-associated HBV DNA was detected only in those HBsAg carriers whose PBMCs contained HBV DNA forms resembling replicative intermediates (1.0-3.2 kilobase pairs in the EcoRI digests). Analysis of PBMC subsets revealed that replicating forms of the HBV genome were present primarily in monocytes. Low levels of hybridization also were detected in B cells, whereas the T cell fraction (which contained natural killer cells) appeared to be devoid of these replicating forms.

In this study, peripheral-blood mononuclear cells from patients with chronic hepatitis B and spontaneous or therapy-induced disappearance of HBsAg were examined for HBV DNA. Samples were evaluated by in situ hybridization and polymerase chain reaction both before and after clearance of HBsAg. By in situ hybridization, positive signals were observed in 2 of 13 samples collected after HBsAg loss, in 8 of 15 samples before HBsAg loss and in 0 of 4 control patients without serological markers of active or prior HBV infection. When polymerase chain reaction analyses were performed, HBV DNA was detected in 5 of 12 HBsAg-negative samples and 10 of 15 HBsAg-positive samples from the study group. Testing of mononuclear cells after disappearance of HBsAg revealed that two of eight patients were HBV DNA positive by in situ hybridization and by polymerase chain reaction, whereas two additional patients were positive by polymerase chain reaction alone. Mononuclear cell-associated HBV DNA was detected between 2 and 9 mo after the disappearance of circulating HBsAg by in situ hybridization and as long as 4 yr later by polymerase chain reaction. These data indicate that patients who have undergone HBsAg seroconversion may nonetheless harbor HBV DNA in their peripheral-blood mononuclear cells for prolonged periods.