Scientists identify new and beneficial function of endogenous retroviruses in immune response

Retroviruses are able to insert into the genomic DNA of cells they
infect, including germ cells. In this way, and by a process called
retrotransposition, they have become a major part of the genome of each
person. About 45 percent of a person's DNA is of retroviral origin, and
some of the better preserved copies are termed "endogenous retroviruses"

Writing in the journal Science, the researchers found that
when B cells are activated by large polymeric antigens such as
polysaccharides of bacteria, they rapidly produce protective antibodies
in what is termed the Type II T-independent antibody response. This
response, central to the body's defense against common bacterial and viral pathogens, is dependent on ERV.

Within activated B cells, the ERV are driven to express RNA copies of
themselves, which in turn are copied into DNA by an enzyme called
reverse transcriptase. The RNA copies of ERV are detected by a protein
called RIG-I, and the DNA copies are detected by another protein called
cGAS. These two proteins send further signals that enable the B cells to
sustain their activated state, proliferate, and produce antibodies.

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