Autoimmune diseases:
Autoimmune diseases occur when the immune system mistakenly attacks the body's own cells and tissues instead of foreign invaders like bacteria or viruses. This occurs due to a loss of the immune system's ability to distinguish self-cells from non-self cells. As a result, the immune system launches an immune response against normal healthy cells, leading to inflammation and damage to various organs and tissues.

Loss of self-recognition:
In higher vertebrates, the immune system has the ability to recognize self-cells and non-self cells. This is achieved through the recognition of specific markers called major histocompatibility complex (MHC) antigens, which are present on the surface of all nucleated cells. These markers help the immune system distinguish between self and non-self cells.

Genetic abnormality:
When there is a genetic abnormality or mutation that affects the immune system's ability to recognize self-cells, the immune system may no longer be able to distinguish between self and non-self cells. This can lead to the immune system mistakenly attacking self-cells, triggering an autoimmune response.

Autoimmune response:
When the immune system mistakenly recognizes self-cells as foreign or harmful, it launches an immune response against these cells. This immune response involves the activation of immune cells, such as T cells and B cells, which produce antibodies and inflammatory molecules. These immune cells and molecules target and attack the self-cells, leading to inflammation, tissue damage, and dysfunction of the affected organs.

Examples of autoimmune diseases:
There are over 80 known autoimmune diseases, each affecting different organs and tissues in the body. Some examples of autoimmune diseases include:

1. Rheumatoid arthritis: The immune system attacks the joints, causing inflammation, pain, and joint damage.
2. Systemic lupus erythematosus: The immune system attacks various organs, including the kidneys, heart, lungs, and skin, leading to inflammation and damage.
3. Multiple sclerosis: The immune system attacks the protective covering of nerve fibers in the central nervous system, leading to communication problems between the brain and the rest of the body.
4. Type 1 diabetes: The immune system attacks and destroys the insulin-producing cells in the pancreas, resulting in high blood sugar levels.
5. Hashimoto's thyroiditis: The immune system targets and damages the thyroid gland, leading to an underactive thyroid.

Conclusion:
When the immune system loses its ability to distinguish self-cells from non-self cells, it can result in autoimmune diseases. These diseases are characterized by the immune system mistakenly attacking and damaging the body's own cells and tissues, leading to inflammation and dysfunction of various organs. Proper understanding and management of autoimmune diseases are crucial for maintaining the health and well-being of affected individuals.