How does the immune system distinguish between self and non-self cells?

The immune system distinguishes between self and non-self cells primarily by using markers known as antigens that are present on the surfaces of cells. These antigens are specific molecules or molecular structures that elicit an immune response. Self-cells typically have self-antigens, which are recognized by the immune system as part of the body's own tissues. Non-self cells, such as pathogens like bacteria and viruses, possess foreign antigens that the immune system recognizes as potential threats.

When the immune system encounters a cell, it assesses the antigens on the cell's surface. If the antigens match those recognized as self, the immune response is usually muted or absent, preventing the immune system from attacking its own tissues. Conversely, if the antigens are foreign (non-self), the immune system can activate various immune responses to eliminate the perceived threat, including the stimulation of T-cells and B-cells, leading to antibody production.

In contrast, while the production of antibodies is an important part of the adaptive immune response and helps in identifying and neutralizing threats, it is the recognition of antigens that initially informs the immune system whether to activate an immune response. Activating T-cells is also part of that response but does not encompass the whole mechanism of distinguishing self