The immune system of a pregnant woman is altered during pregnancy , but not in the way believed, according to the results of a study conducted at Linköping University in Sweden. This shows that the thymus , an organ of the immune system located near the heart, plays an important role during a normal pregnancy in ensuring that the mother’s immune system protects her against infection while also getting the body to tolerate the fetus.
Researchers have questioned for many decades how the body handles the paradox that arises when a woman becomes pregnant. On the one hand, the mother’s immune system must adapt so that it does not react with rejection of the fetus (half of whose genes come from the father, making it a partially foreign object). On the other hand, the immune system must provide effective protection against infection.
This study, published in the “Journal of Allergy and Clinical Immunology,” has investigated how the immune system of a pregnant woman changes during a normal pregnancy. They have studied, in particular, the role played by a small organ, the thymus , in immune regulation.
The thymus plays a central role in the development of a very important group of cells in the immune system, T cells. T cells act as an orchestral conductor and determine how the immune system reacts . The body’s own cells must be tolerated, while foreign objects like bacteria and viruses must be attacked.
Despite the central role of the thymus in the overall immune system, it is not known whether its function changes during pregnancy. Most of what is currently known about the thymus comes from studies in mice. In general, it is believed that, according to animal studies, the thymus becomes smaller during pregnancy and that its production decreases and fewer cells are released.
In animals, a decrease in the number of T cells causes a weakening of the immune defense, which means that the fetus can be tolerated. But is it the same in humans? To answer this question, the researchers studied the production of different types of T cells in the blood of 56 pregnant women and 30 non-pregnant women. They were particularly interested in a type of T cell, known as regulatory T cells.
“We have shown that thymus T cell production does not change in pregnancy . We have also shown that the production of regulatory T cells, which can weaken the immune response, appears to increase in pregnancy. These results may explain how the mother can not only tolerate the fetus, but can also maintain its defense against infection, “says Sandra Hellberg, a doctoral student in the Department of Clinical and Experimental Medicine at Linköping University, and one of the authors of the study.
The discovery may also be important in understanding certain autoimmune diseases, in which the body’s immune system begins to attack the body’s own cells. Several autoimmune diseases are connected to thymus function: an example is multiple sclerosis , in which the brain and spinal cord are damaged by the immune system.
“Previous research on multiple sclerosis has shown that thymus function is impaired in the disease and that T-cell production is lower. This could explain why the symptoms of women with multiple sclerosis often improve during pregnancy, “concludes Professor Jan Ernerudh, research director of the study