http://en.wikipedia.org/wiki/Phagocyte
Phagocytosis is common and probably appeared early in evolution,evolving first in unicellular eukaryotes.Amoebae are unicellular protists that separated from the tree leading to metazoa shortly after the divergence of plants, but they share many specific functions with mammalian phagocytic cells.Dictyostelium discoideum, for example, is an amoeba that lives in the soil and feeds on bacteria. Like animal phagocytes, it engulfs bacteria by phagocytosis mainly through Toll-like receptors, and it has other biological functions in common with macrophages.Dictyostelium discoideum is social; it aggregates when starved to form a migrating pseudoplasmodium or slug. This multicellular organism eventually produces a fruiting body with spores that are resistant to environmental dangers. Before the formation of fruiting bodies, the cells can migrate as slug-like organisms for several days. During this time, exposure to toxins or bacterial pathogens has the potential to compromise survival of the amoebae by limiting spore production. Some of the amoebae engulf bacteria and absorb toxins while circulating within the slug, and these amoebae eventually die. They are genetically identical to the other amoebae in the slug, and their sacrifice of themselves to protect the other amoebae from bacteria is similar to the self-sacrifice of phagocytes seen in the immune system of humans. This innate immune function in social amoebae suggests an ancient cellular foraging mechanism that may have been adapted to defense functions well before the diversification of the animals.But a common ancestry with mammalian phagocytes has not been proven. Phagocytes occur throughout the animal kingdom,from marine sponges to insects and lower and higher vertebrates.The ability of amoebae to distinguish between self and non-self is a pivotal one and is the root of the immune system of many species.
Phagocytosis is common and probably appeared early in evolution,evolving first in unicellular eukaryotes.Amoebae are unicellular protists that separated from the tree leading to metazoa shortly after the divergence of plants, but they share many specific functions with mammalian phagocytic cells.Dictyostelium discoideum, for example, is an amoeba that lives in the soil and feeds on bacteria. Like animal phagocytes, it engulfs bacteria by phagocytosis mainly through Toll-like receptors, and it has other biological functions in common with macrophages.Dictyostelium discoideum is social; it aggregates when starved to form a migrating pseudoplasmodium or slug. This multicellular organism eventually produces a fruiting body with spores that are resistant to environmental dangers. Before the formation of fruiting bodies, the cells can migrate as slug-like organisms for several days. During this time, exposure to toxins or bacterial pathogens has the potential to compromise survival of the amoebae by limiting spore production. Some of the amoebae engulf bacteria and absorb toxins while circulating within the slug, and these amoebae eventually die. They are genetically identical to the other amoebae in the slug, and their sacrifice of themselves to protect the other amoebae from bacteria is similar to the self-sacrifice of phagocytes seen in the immune system of humans. This innate immune function in social amoebae suggests an ancient cellular foraging mechanism that may have been adapted to defense functions well before the diversification of the animals.But a common ancestry with mammalian phagocytes has not been proven. Phagocytes occur throughout the animal kingdom,from marine sponges to insects and lower and higher vertebrates.The ability of amoebae to distinguish between self and non-self is a pivotal one and is the root of the immune system of many species.
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