How does the body differentiate between self and non-self cells?

The body differentiates between self and non-self cells primarily through the recognition of specific markers, known as antigens. These antigens are unique molecules or structures found on the surface of cells. Self-cells, such as the body’s own tissues, display markers that are recognized as familiar by the immune system. In contrast, non-self cells, such as pathogens (bacteria, viruses) or foreign substances, have distinct markers that do not match the body's own and are therefore recognized as threats.

This recognition is critical for the immune response. When the immune system identifies a non-self antigen, it triggers various immune mechanisms to eliminate the foreign invader. This process is central to the operation of lymphocytes (T-cells and B-cells), which are highly specialized in recognizing these markers and mounting an appropriate response.

In contrast, size, presence of antibodies, and the speed of cell division do not directly relate to the mechanism of self versus non-self discrimination. Size can vary widely among different types of cells and does not indicate whether a cell is self or non-self. Antibodies play a role in the immune response after self/non-self differentiation has occurred; they are produced in response to non-self antigens but are not tools for differentiation themselves.