August 20, 1998-The human immune system, an elegant and intricate biological defense system unmatched in most life forms, may have evolved from a mobile piece of DNA that inserted itself into the mammalian genome more than 450 million years ago.
A team of researchers led by David G. Schatz at the Howard Hughes Medical Institute at Yale University has found evidence that tiny gene particles vital to the task of producing millions of different kinds of antibodies act like a gene segment that can "jump" into foreign DNA. Although there are many examples of such genes in lower organisms, it is the first cut-and-paste "transposase" ever found in humans.
"This helps explain why the jawed vertebrates are the only species that have a second, adaptive immune system, in addition to the innate immune system that all other species have," says Schatz, an immunologist. His study, conducted with Yale researchers Alka Agrawal and Quinn M. Eastman, is published in the August 20 issue of the journal Nature.
An adaptive immune system relies on two lines of defense to detect and destroy invaders. Both parts of the immune system belong to a class of white blood cells called lymphocytes, found in the blood and lymphoid organs. B lymphocytes produce antibodies that bind tightly to a foreign molecule, inactivating it or marking it for destruction by other cells in the immune system. T lymphocytes detect the presence of foreign molecules inside special "processing" cells once those cells have displayed a fragment of the foreign molecule-those pieces are called antigens-on the processing cell's surface. So-called T-cell receptors on the surface of the T lymphocyte bind strongly to the antigen.
Although they perform different functions, both B and T lymphocytes use the same
unique genetic mechanism to economically generate an almost unlimited number of
antibodies and T-cell receptors. Indeed, the human immune system is capable of
producing a larger number of different ant
Contact: Jim Keeley
Howard Hughes Medical Institute