Immunological phylogeny

Article By:

Marchalonis, John J. Department of Biochemistry, Medical University of South Carolina, Charleston, South Carolina.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.338680

The study of immunology and the immune system in evolution. All vertebrates can recognize and respond to nonself-molecular configurations on microorganisms, cells, or organic molecules by utilizing a complex recognition system termed the immune response. The presence of lymphocytes and circulating antibodies has been documented in all extant vertebrate species, ranging from the ostracoderm-derived cyclostomes, such as hagfish and lampreys, to mammals. However, the existence of induced, specific reactions directly homologous to the immune repertoire of vertebrates has not been clearly established in invertebrates. Studies have been done which focused on the presence and characterization of cells of the T and B lymphoid series in lower vertebrate species; the nature of the antibodies produced by lower vertebrate species and their relationship to well-characterized immunoglobulin classes of mammals; the extent of diversity in the antibodies of lower vertebrates with particular respect to the degree of variable-region heterogeneity within lower species compared with that exhibited by mammals; and the deoxyribonucleic acid (DNA) sequence of genes encoding variable regions of immunoglobin of lower species. Studies designed to pinpoint the origin of immune diversification have been actively pursued in the protochordates, such as tunicates, and there is also considerable interest in the defense mechanisms of invertebrate phyla not directly related to the evolutionary stream which gave rise to the chordates.

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