Microglia as mediators of inflammatory and degenerative diseases

Microglia are the principal immune cells in the central nervous system (CNS ) and have a critical role in host defense against invading microorganisms and neoplastic cells. However, as with immune cells in other organs, microg lia may play a dual role, amplifying the effects of inflammation and mediat ing cellular degeneration as well as protecting the CNS. In entities like h uman immunodeficiency virus (HIV) infection of the nervous system, microgli a are also critical to viral persistence. In this review we discuss the rol e of microglia in three diseases in which their activity is at least partia lly deleterious: HIV, multiple sclerosis, and Alzheimer's disease.