Self immunity, in the context of immunology, refers to the immune system's ability to distinguish between its own cells (self) and foreign substances (non-self) and to avoid attacking its own tissues. This recognition and tolerance of self is crucial for preventing autoimmune diseases.
Here's a breakdown of the concept:
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The Immune System's Core Function: The primary role of the immune system is to protect the body from harmful invaders like bacteria, viruses, and parasites. To do this effectively, it needs to be able to identify and eliminate anything that's not part of the body.
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Self vs. Non-Self Discrimination: The immune system accomplishes this by recognizing specific molecules, called antigens. These antigens are present on the surface of cells and other substances. The immune system learns to recognize which antigens belong to the body's own cells (self-antigens) and which are foreign (non-self antigens).
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Tolerance of Self: "Self immunity" is essentially a state of tolerance towards the body's own tissues. This tolerance is established through several mechanisms, primarily during the development of immune cells (lymphocytes) in the thymus (for T cells) and bone marrow (for B cells).
- Central Tolerance: Immature T and B cells that recognize self-antigens strongly are either eliminated (negative selection) or rendered inactive (anergy) during their development.
- Peripheral Tolerance: Even if some self-reactive T and B cells escape central tolerance, mechanisms in the peripheral tissues (outside the thymus and bone marrow) prevent them from causing harm. These mechanisms include:
- Anergy: T cells become unresponsive to antigens.
- Suppression: Regulatory T cells (Tregs) actively suppress the activity of other T cells, including those that might react against self-antigens.
- Ignorance: T cells simply don't encounter the self-antigen in a way that triggers an immune response.
- Apoptosis: Self-reactive lymphocytes undergo programmed cell death.
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Failure of Self Tolerance: Autoimmunity: When self-tolerance mechanisms fail, the immune system can mistakenly attack the body's own tissues, leading to autoimmune diseases like:
- Type 1 Diabetes: The immune system attacks insulin-producing cells in the pancreas.
- Rheumatoid Arthritis: The immune system attacks the joints.
- Multiple Sclerosis: The immune system attacks the myelin sheath that protects nerve fibers.
- Systemic Lupus Erythematosus (SLE): The immune system can attack various organs and tissues throughout the body.
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Evolution of Understanding: The concept of self/non-self discrimination has evolved considerably. Initially, it was thought that the immune system simply distinguished between self and non-self. However, more recent research highlights the importance of regulatory mechanisms and the complex interplay between different immune cells in maintaining tolerance. The original reference highlights adaptive immunity which involves the ability of lymphocytes to differentiate between self and non-self-antigens.
In summary, self immunity is the critical ability of the immune system to recognize and tolerate its own tissues, preventing harmful autoimmune reactions.
