Rapid isolation of highly enriched and quiescent microglia from adult rat hippocampus: immunophenotypic and functional characteristics

Isolation of microglia from CNS tissue provides a powerful tool to study basic microglia biology and examine the effects of in vivo treatments on microglia immunophenotype and function. Previous microglia isolation methodologies utilized whole brain. However, microglia immunophenotype varies across CNS anatomical loci, thus isolation of microglia from whole brain may obscure regional brain variations in microglia immunophenotype and function. In addition, it is unknown to what extent microglia isolation procedures alter the in situ immunophenotype and function of microglia. The present report details a procedure for the rapid isolation of microglia from discrete CNS anatomical loci and addresses the issue of whether the in situ microglia immunophenotype is significantly altered by the isolation procedure. The present microglia isolation method yielded highly enriched hippocampal microglia, which were devoid of other CNS macrophage subtypes and exhibited attributes reflecting a quiescent phenotype characteristic of microglia observed in situ under non-pathological conditions. Further, isolated microglia exhibited functional responsiveness to immunogenic stimuli ex vivo. The immunophenotypic and functional attributes of isolated microglia suggest that the isolation procedure preserves the in vivo phenotype of microglia, thus providing an experimental method with minimal procedural confounds for examining in vivo treatments on microglia ex vivo.