Immunology and bioinformatics found evidence of the benefits that could bring people familial Mediterranean fever. The carriers of this mutation defective protein is formed, which allows some bacteria to suppress inflammatory response of the immune system, among these bacteria and the plague Bacillus. Thus, the plague probably helped the mutation to gain a foothold and spread in the Mediterranean countries, and fever in turn, saving people from infection. Work published in the journal Nature Immunology.
Familial Mediterranean fever is a hereditary autoimmune disease. Its carriers are overly active protein Pirin, which induces the release of proinflammatory cytokines in blood and inflammatory type of the death of immune cells (piropos). Therefore, such people and then there are the bouts of fever and acute pain resembling a real inflammation of the intestines. Until recently, this disease is caused severe complications, such as renal amyloidosis, but now the attacks are often able to stop.
As the name implies, it is widespread in the Mediterranean — there is a mutation rate is about 10 percent. However, it is still unclear why the mutation was fixed in this region. This phenomenon can think of two explanations: either the culprit genetic drift (i.e. in the Mediterranean migrated more carriers of this mutation than healthy carriers of the gene variant), or it is supported by some factor of selection, which was geographically restricted and operated only in this region.
A group of researchers under the leadership of Jae Jin, Jae (Jae Jin Chae) from the National Institute of human genome research in the US suggested that such a selection factor could be the plague. Despite the fact that many pathogenic bacteria produce toxins, inhibiting the body’s inflammatory response, the plague Bacillus Yersinia pestis and its closest relatives has acquired an additional toxin, which directly blocks the Pirin and its complexes with other proteins. Therefore, excessive activity of Pirin could be useful to survive during the plague.
To test their hunch, the researchers studied the genetic data of 2313 inhabitants of modern Turkey. Among them, scientists have discovered two relatively common mutations in the gene Pirin mountains. In addition, in the areas adjacent to this gene was reduced mutation rate, indicating a positive selection, together with a mutant gene in the population of Pirin entrenched and neighboring mutations. The authors constructed several models to determine the time of appearance of mutations in the Pirin mountains. According to one of them, they appeared about three and a half thousand years ago, or that about two thousand years ago. However, the selection began to act on them later — during the first (541-767.) and the second (1346-1875 years) pandemics of plague. Researchers believe that the second pandemic had a strong influence on the fixation of mutations.