When immune system goes rogue

Immune system is a system of the body that protects it from all foreign substances from the outside (viruses, bacteria, fungi, etc.) and controls the destruction of failed or outdated cells (for example, it is immunity that protects us from tumour formations). In order for immune cells not to destroy the cells of their own body, there is immunological tolerance.

During the development of the immune system lymphocytes undergo "training" in the thymus and lymph nodes. At the same time, each clone of cells acquires the ability to recognize certain foreign proteins in order to fight various infections in the future. Some lymphocytes learn to recognize the proteins of their body as foreign. Their main goal is to destroy defective or diseased cells of the body. The amount and activity of such lymphocytes is kept under control by the immune system. However, in some people, control over these cells is lost, their activity increases and the process of destruction of normal cells starts - an autoimmune disease develops.

The most well known example (not the most common case) of an autoimmune disease is rheumatoid arthritis, which occurs when the immune system attacks the joints, causing inflammation and thickening of the joint capsule. Reiter's syndrome, caused by a chlamydial infection, is another example of an autoimmune disease. Urethritis, inflammatory diseases of the eyes, mouth ulcers that accompany chlamydial infection are not caused by the bacteria themselves, but by the immune system.

Sometimes the mother's immune system can perceive the child's body as a foreign body. Platelet antigens are inherited from both mother and father. If antibodies specific to platelet antigens are present in the fetus but absent in the mother, they may be recognized by the mother's immune system as foreign, with subsequent formation of alloreactive antibodies that cross the placenta. This can result in the fetus not being able to grow in the womb or causing a miscarriage.

Another possible case where the mother's immune system can attack the fetus is when there is a mismatch between the mother's and the baby's blood type, and the mother's immune system overreacts to the baby's red blood cells and her antibodies attack them. In fact, this happens very rarely, although the blood type of mother and child is very often different.

For a woman's immune system, sperm is also a foreign body, as it contains proteins foreign to her body, so it will attack the sperm, reducing the likelihood of fertilization. This response to sperm could either be an adaptive strategy to neutralize ejaculate with potentially harmful pathogens, or a way to allow the more fertile partner's sperm to successfully fertilize, thereby increasing the fitness of her future offspring.