Genome Complexity; Human Immunity (Introduction)

by David Turell , Friday, July 17, 2015, 16:23 (3418 days ago) @ David Turell

An example of automatic high speed mutations are seen in B cells as the immune system gears up quickly to fight infections by creating antibodies that form a library of defense for the present and the future:-http://www.sciencedaily.com/releases/2015/07/150716160559.htm-"Within germinal centers, B cells evolve in a Darwinian-like fashion. The gene responsible for producing their antibodies mutates rapidly, a million times faster than the normal rate of mutation in the human body, and the cells proliferate. B cells whose mutations increase the antibody's affinity for the antigen are selected, and these cells then continue to mutate and proliferate.-"'Previously, we showed that high affinity cells spend more time dividing and mutating in between rounds of competition. We now show that these high affinity cells also use this additional time more effectively -- by dividing at faster rates," Gitlin says. In this manner, the germinal center produces the high affinity antibodies that are the basis of an effective immune response.-***-"The team's research has focused on the dynamics inside the germinal center. Within it, B cells travel between two areas known as the dark zone and the light zone. In the dark zone, the B cells mutate and proliferate, before traveling to the light zone, where they pick up pieces of antigen. The higher the affinity of their antibodies, the more antigen they pick up.-"Their previous experiments demonstrated that another type of immune cell, the T cell, operates in the light zone to recognize the higher affinity B cells based on the amount of antigen they display. The more antigen the B cells present to T cells, the stronger the signal the T cells send. As a result, the high affinity B cells spend more time in the dark zone in between visits to the light zone.-***-"By labeling DNA replication and following its progression, the team took a close look at how the S phase of the cell cycle, in which the cell copies its DNA in preparation for division, is sped up. They found that acceleration during this phase was due to the double-stranded DNA molecule being unzipped and copied more rapidly at the so-called replication fork.-"'Together, these studies describe two complementary ways in which signals from T cells empower the best equipped set of B cells to take over the immune response during affinity maturation."-Comment: This is the only example I know of that fits dhw's 'inventive mechanism' where cells can mutate at will for a specified purpose.