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The cells, a subset of immune-system B cells, make autoantibodies, which bind to and attack the body’s own tissue. The researchers report, that they found higher levels of these cells in elderly female mice, young and old mice prone to autoimmune disease, and humans with autoimmune diseases.
Autoimmune diseases occur when the immune system begins attacking its own tissues rather than external pathogens. Several autoimmune diseases, including lupus, rheumatoid arthritis and multiple sclerosis, afflict women anywhere from two to ten times as often as they do males. Although sex hormones are known to play a role in autoimmune disease, other factors are involved in these gender differences.
The research team came across the new cells when they were examining differential expression of X chromosome genes in healthy male and female mice. They discovered a previously undescribed type of B cell, which expressed the cell-surface protein CD11c. The protein is an integrin, which helps cells attach to other cells or to an extracellular matrix.
These cells increase as healthy female mice age, but remain at constant low levels in healthy male mice. As a result, the researchers named the cells Age-associated B Cells or ABCs. The researchers also found higher levels of ABCs in young and old mice that are prone to autoimmune disease. They could detect the elevated ABC levels before any disease developed and even before autoantibodies appeared, suggesting a role for these cells in early detection of disease.
The researchers also found an almost identical type of cell in the blood of many human autoimmune patients. In women with rheumatoid arthritis the presence of these cells increased with age.
The researchers also found that activation of these cells requires stimulation of TLR7, a cell-surface receptor involved in innate immune responses. The gene for TLR7 is located on the X chromosome. Women have two X chromosomes, men an X and a Y chromosome. Normally one copy of the X chromosome in women is silenced so that it does not produce excess protein. But the silencing is not always complete, and women commonly express elevated levels of some X chromosome genes.
MEDICA.de; Source: National Jewish Health