Microglia are resident macrophage cells in the brain, that promptly react in response to toxins in their microenvironment and quickly proliferate, become hypertrophic, and persistently increase the expression of a large number of marker molecules, such as Mac-1 and TNF-α [44], and are further transformed to macrophage-like cells in patients with PD [45]. The gene discussed is TNF; the disease is Parkinson disease.