Human microglial cell isolation from adult autopsy brain: Brain pH, regional variation, and infection with human immunodeficiency virus type 1

Microglia are the main source of productive infection by human immunodeficiency virus type 1 (HIV-1) in the central nervous system (CNS). Infection of microglia is difficult to study because nonhuman microglia are not infected by HIV-1, adult human microglia from surgically removed brain tissues are scarce, and fetal human microglial cells differ from adult cells in potentially important ways. Adult autopsies are a potential source of brain tissue for HIV-1 research, but the technique of isolating and infecting cells postmortem is not completely standardized. The authors determined optimal conditions for isolating and infecting adult microglial cells using 18 adult autopsy brain specimens from HIV-1-infected and noninfected decedents. The yield of mixed glial cells overall was on average 0.5 × 10⁶ cells per gram of wet tissue. There was no correlation between the number of microglia isolated and the postmortem interval (PMI), HIV seropositivity, age, or gender. Brain pH accounted for about 41% of yield variability; a pH of less than 6.0 generally was not compatible with adequate cell recovery. The highest microglial cell yields were derived from anterior brain sectors (frontal lobe and temporal lobe) versus occipital lobe and cerebellum. A PMI of up to 25.5 h produced excellent cell yields in frontal lobe samples with high brain pH. HIV-1 infection of frontal lobe microglia was 100% successful using both CXCR4- and CCR5-tropic strains of HIV-1. With proper selection of cases and brain region, autopsy brain specimens are a dependable source of viable microglial cells to study CNS HIV-1 infection.