What strategy does the immune system use to recognize self vs. non-self cells?

The immune system utilizes antigen recognition as its primary strategy to differentiate between self and non-self cells. This process is crucial for the development and function of immune responses. Cells of the immune system, particularly B cells and T cells, possess specialized receptors that are designed to recognize specific proteins or molecules (known as antigens) found on the surface of pathogens or foreign cells. Each individual’s body cells have unique identifiers known as major histocompatibility complex (MHC) molecules that present self-antigens.

When immune cells encounter cells with antigens that are recognized as foreign—those that do not match the self-antigens—they initiate an immune response. This is a fundamental mechanism that prevents the body from attacking its own cells, thus maintaining self-tolerance while allowing the immune system to effectively eliminate threats from pathogens. The specificity of antigen recognition is what allows the immune system to target and neutralize non-self entities, such as bacteria, viruses, and transplanted tissues, while sparing the body’s own cells.