During the progression of HD, activated microglia release neurotrophic mediators that include nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CNTF), and transforming growth factor-beta (TGF-β), which have beneficial effects (i.e., trophic activity and phagocytosis) in neurodegenerative lesions. Here, GDNF is linked to Huntington disease.