Fragments of ancient genome of viruses embedded in human DNA, involving the formation of our immune system.
It is known that retroviruses can be embedded in the DNA of an organism that infects. A endogenous retroviruses also pass on their genetic material to descendants of the infected individual.
Finally, after millions of years of evolution in the human genome (and animals too) has accumulated a lot of "remnants" of ancient viral infections. The irony is that these fragments have become not just ballast, and were an important part of DNA. They participate in the formation of innate immunity and help to resist the dangerous microorganisms and "modern" viruses.
Scientists from the University of Utah have worked with interferon - a protein secreted in the protective reaction of the body for viruses. It increases the activity of genes involved in the immune response.
The scientists treated gamma-interferon several cells and concluded that many genes are activated they were fragments of the genome of the ancient viral infections. Then they cut out the fragments of the DNA of cells and infected them with a new dangerous virus. After this "operation" to issue a normal immune response the modified cells have failed.