Non-self

In immunology and biology, 'non-self' refers to anything foreign to an organism's body, triggering an immune response. It encompasses a broad spectrum, including pathogens like bacteria, viruses, and fungi, as well as foreign molecules (antigens) like pollen or mismatched blood cells. The immune system distinguishes between 'self' (the organism's own tissues and cells) and 'non-self', attacking and eliminating the latter to maintain health. This crucial distinction prevents the body from attacking itself and protects it from external threats. The concept is fundamental to understanding immunity, autoimmunity, and transplant rejection.

Non-self meaning with examples

• Upon encountering a bacterial infection, the body's immune system rapidly identifies the bacteria as 'non-self'. This triggers a cascade of events, including the activation of white blood cells to engulf and destroy the invading bacteria. The recognition process relies on specific receptors that differentiate between the host's cells and the bacterial antigens. This immune reaction aims to protect the body from the infection and prevent disease.
• In organ transplantation, the recipient's immune system often perceives the donor organ as 'non-self' due to differences in cell surface markers. Consequently, the immune system initiates an attack, leading to organ rejection. Immunosuppressant drugs are administered to suppress the immune response and reduce the risk of rejection, thereby allowing the transplanted organ to function effectively within the recipient's body.
• When someone receives a blood transfusion, the immune system must correctly identify whether the donor's blood type is compatible, in order to avoid treating the donor's blood as 'non-self' due to mismatched antigens on red blood cells. If incompatible blood types are mixed, the immune system will attack the foreign blood cells, leading to a potentially life-threatening reaction called an incompatible transfusion.
• Certain autoimmune diseases arise when the immune system malfunctions and starts recognizing the body's own tissues and cells as 'non-self', and subsequently attacking them. For example, in rheumatoid arthritis, the immune system attacks the joints. Similarly, in type 1 diabetes, the immune system targets and destroys the insulin-producing cells in the pancreas. These disorders are the result of this aberrant response to what should be recognised as self.