Microglia, also called Hortega cells, are immune cells that reside in the brain and spinal cord. They constitute the supporting structure of the central nervous system (CNS). The basic function of these cells is to defend and repair the brain from injuries caused by invading microorganisms, cellular debris, and disease.
Generally, microglia comprise the main component of the CNS immune system. They constantly scan the CNS for damaged plaques, neurons, and infectious agents. There are many types of these cells in the CNS, including ameboid, ramified, astrocytes, oligodendrocytes, and ependymocytes.
Microglia perform a wide range of immune response and defense functions within the CNS. They are sensitive to the environment and are able to detect the smallest changes in the biological makeup of the brain tissue. The cells scan the CNS to locate and neutralize any plaques, deoxyribonucleic acid (DNA) fragments, neural tangles, dead cells, damaged cells, and foreign materials. They can be considered the housekeepers of the brain by cleaning up cell debris.
Typically, microglia are involved in the phagocytosis of foreign materials — the process of engulfing and killing bacteria, viruses, lipids, cellular waste and other substances. The cells destroy infectious organisms by releasing a variety of cytotoxic material — toxic substances that damage cells and cause neuron death. Cytotoxic secretions destroy bacteria, viruses, and infected neurons, but excessive cytotoxic amounts can cause nerve damage.
Microglia play a key role in neuro-degeneration, which is the progressive loss of neurons from the brain that can lead to disability and death. They delay the progression of Alzheimer’s disease — a neuro-degenerative disease in which the brain develops abnormal clumps of cells and tangled neurons. The cells are also involved in managing and reducing the progression of Parkinson’s disease, which is a movement disorder of the CNS that impairs the speech, motor skills, and other bodily functions.
The cells also play an important role in managing infectious viruses, such as the human immunodeficiency virus (HIV) and herpes simplex virus. Microglia release neurotoxic secretions that battle HIV. Additionally, they release cytotoxic substances that aim to neutralize the herpes simplex virus.
Microglia are active in defending the CNS from bacterial infections. They manage streptococcus pneumoniae — the bacterium that causes meningitis. The cells are involved in protecting the brain and spinal cord from parasitic infections, as well.
Plasmodium falciparum is a parasite that causes malaria in humans. While most instances of malaria are easily treated, cerebral malaria is a serious complication that results when red blood cells break into the brain tissue and cause ischemia — a restriction in blood supply that causes dysfunction or damage to tissue. Microglia are also involved in the phagocytosis of cerebral malaria and minimize the damage caused by it.
