In Vivo Infection of Ramified Microglia from Adult Cat Central Nervous System by Feline Immunodeficiency Virus

Abstract

Infection of microglial cells by the human immunodeficiency virus (HIV) is supposed to play an important role in the pathogenesis of AIDS-related central nervous system (CNS) complications. So far, however, experimental data about interactions between HIV and ramified microglia from the adult CNS were only occasionally reported, making it difficult to understand the exact nature of pathogenic events contributing to HIV-encephalopathy. Therefore, we used the animal model of feline immunodeficiency virus (FIV) infection of domestic cats to establish an experimental system which is suitable for studying the relationships between an immunodeficiency virus and the mature ramified microglia of the central nervous system. By means of density gradient centrifugation approximately 95% pure microglial cells could be isolated from adult feline brain that were characterized by their CD45(low) phenotype. Resident microglia extracted from the CNS of experimentally infected cats harbored FIV-specific DNA and cocultivation with mitogen-activated, but uninfected peripheral blood mononuclear cells (PBMC) resulted in recovery of high-titered infectious virus. Double labeling of brain cell monocultures explanted from persistently infected animals for both microglia and FIV markers disclosed less than 1% of viral antigen expressing microglial cells. This suggests that during the subclinical phase of the infection only a small number of brain-resident macrophages are productively infected. However, interaction of FIV-infected microglia and inflammatory lymphocytes may promote viral replication, thus supporting viral spread in brain tissue.

In Vitro Activation of Feline Immunodeficiency Virus in Ramified Microglial Cells from Asymptomatically Infected Cats

“…Moreover, there are interesting suggestions and findings which open up the prospect that instead of suppressing viral replication, T lymphocytes can enhance virus release from lentivirus-infected cells of the monocyte/ macrophage lineage (27,28). This is in line with recent findings from our laboratory indicating that recovery of infectious feline immunodeficiency virus (FIV) from microglia isolated from adult FIV-infected cats is achievable only by cocultivation with mitogen-activated T lymphoblasts (17). Since early stages and subclinical persistence of lentiviral CNS infection are accompanied by mild inflammatory reactions in the brain, including T-lymphocyte infiltration (16), it seemed likely to us that during clinically silent infection of the CNS, multiple contacts of infected microglia with CNS-patrolling T lymphocytes might result in a microburst of viral replication.…”

“…The preparation of virus stocks has been previously described (17) Ramified microglia from adult feline brain. Microglial cells were extracted from adult feline cat brain using an isolation method that was published previously (17).…”

“…The preparation of virus stocks has been previously described (17) Ramified microglia from adult feline brain. Microglial cells were extracted from adult feline cat brain using an isolation method that was published previously (17). In brief, the brain and brain stem were aseptically removed, meninges were stripped off, and the remaining tissue was mechanically disrupted by mincing through a stainless steel sieve.…”

“…Therefore, caution should be taken in extrapolating data from fetal cells to events which take place in adult microglial cells infected by immunodeficiency virus. Nevertheless, occasional reports on the interaction of lentiviruses with microglia from nonfetal tissue show that microglial cells, although principally supporting viral replication, usually do not do so ex vivo when isolated from neurologically asymptomatic infected hosts (6,7,11,17).…”

Upregulation of RANTES Gene Expression in Neuroglia by Japanese Encephalitis Virus Infection

“…The activation of glia by viral infection could lead to the restriction of viral spreading, whereas the consequence is frequently CNS dysfunction and/or destruction (6,13,28,55,68,69). Elevated concentrations of chemokines may be partially responsible for neuronal death in various diseases, including viral infection (2).…”