Microglia
Research has discovered dystrophic (defective development) human microglia. "These cells are characterized by abnormalities in their cytoplasmic structure, such as deramified, atrophic, fragmented or unusually tortuous processes, frequently bearing spheroidal or bulbous swellings." The incidence of dystrophic microglia increases with aging. Microglial degeneration and death have been reported in research on Prion disease, Schizophrenia and Alzheimer's disease, indicating that microglial deterioration might be involved in neurodegenerative diseases. A complication of this theory is the fact that it is difficult to distinguish between "activated" and "dystrophic" microglia in the human brain.
Gliosis
Microgliosis following a CNS insult most commonly involves the development of an altered cellular morphology, specifically the enlargement of cellular processes. The microglial immunological surface receptor CR3 is also upregulated within 24 hours after the initial injury. Within the first week following the injury, microglia begin to proliferate abnormally and while doing so exhibit several immunophenotypic changes, particularly an increased expression of MHC antigens. The population of activated microglia at the site of a CNS injury includes not only endogenous microglia of the CNS but also exogeneous perivascular cells originating in the bone marrow that migrate to the area and transform into microglia to supplement the microgliosis response.