Localization of HIV‐1 in human brain using polymerase chain reaction/in situ hybridization and immunocytochemistry

Abstract

Human immunodeficiency virus type 1 (HIV-1) infects the brains of a majority of patients with the acquired immunodeficiency syndrome (AIDS), and has been linked to the development of a progressive dementia termed "HIV-associated dementia." This disorder results in severe cognitive, behavioral, and motor deficits. Despite this neurological dysfunction, HIV-1 infection of brain cells does not occur significantly in neurons, astrocytes, or oligodendrocytes, but is restricted to brain macrophages and microglia. To identify possible low-level or latent infection of other brain cells, we combined the techniques of the polymerase chain reaction with in situ hybridization for the detection of HIV DNA, and used immunocytochemistry to identify the HIV-expressing cells. In the 21 adult brains studied (15 AIDS and 6 seronegative control brains), we found that polymerase chain reaction/in situ hybridization was both sensitive and specific for identifying HIV-infected cells. In all brains, the majority of infected cells were macrophages and microglia. In several brains, however, a substantial minority of cells harboring HIV DNA were identified as astrocytes. Neurons, oligodendrocytes, and endothelial cells were not infected with HIV, even in cases with HIV-associated dementia. These findings confirm previous data regarding the importance of macrophage/microglial infection, and essentially exclude neuronal infection in pathogenetic models of HIV-associated neurological disease. These data also demonstrate that latent or low-level infection of astrocytes occurs in AIDS, a finding that may be of importance in understanding HIV neuropathogenesis.

Identification and cloning of human astrocyte genes displaying elevated expression after infection with HIV-1 or exposure to HIV-1 envelope glycoprotein by rapid subtraction hybridization, RaSH

“…There is general agreement, however, that HIV-1 can persist in astrocytes for prolonged periods in a low productive, non-cytolytic state, from which it can be induced by physiologic stimuli such as tumor necrosis factor-a (TNF-a) (Shahabuddin et al, 1992;Tornatore et al, 1991). Surveys of autopsy tissues using in situ PCR and sensitive immunocytochemistry techniques indicate that the frequency of HIV-1 positive astrocytes in selected tissue sections from brains of patients with dementia can achieve 1% (Saito et al, 1994;Takahashi et al, 1996;Tornatore et al, 1994a). Considering that the number of astrocytes in the brain is between 10 11 to 10 12 cells (Verkhratsky et al, 1998), these cells clearly constitute a major target for HIV-1 infection in the brain.…”

HIV-1, chemokines and neurogenesis

“…In the central nervous system (CNS), replicating virus has only been found in microglial cells and macrophages (Takehashi et al, 1996;Wiley et al, 1996;Gonzalez-Scarano and Martin-Garcia, 2005). However, infection of the brain by HIV-1 results in widespread neuroinflammatory disease that is accompanied by diverse neuropathological signs, which include the activation of astrocytes and microglia, demyelination, dendritic pruning as well as neuronal death (Price et al, 1988;Kaul et al, 2001).…”

Proteinase-Activated Receptor-2 Induction by Neuroinflammation Prevents Neuronal Death during HIV Infection

“…Neuropathologically, brains of patients with HAD frequently exhibit neuroinflammation, including astrogliosis, multinucleated giant cells, and neuronal apoptosis (16). Despite the severe neuronal loss observed in HIV-1 infection, minimal infection of neurons has been reported (17)(18)(19). This consistent observation has led to the assumption that indirect pathways, including the release of host inflammatory molecules such as cytokines, chemokines, and matrix metalloproteases, in addition to other potential host neurotoxins and also HIV-encoded proteins, Tat and gp120, play central roles in HIVinduced neuronal death (20 -24).…”