What term describes the mechanism by which an antibody fits its antigen?

The term that describes the mechanism by which an antibody fits its antigen is often referred to as the "lock and key fit." This analogy illustrates how the specific structure of an antibody (the "lock") is designed to bind with a particular antigen (the "key"). This interaction is crucial for the antibody's ability to recognize and neutralize pathogens effectively.

In this context, the lock and key concept emphasizes the high specificity of the antibody-antigen interaction, where only the correct "key" (antigen) can fit into the "lock" (antibody's binding site). This specificity is vital for the immune system's ability to distinguish between harmful invaders and the body's own cells.

Other terms like affinity, antigenic specificity, and complementarity relate to aspects of the antibody-antigen interaction as well. Affinity refers to the strength of the binding interaction between the antibody and antigen, while antigenic specificity denotes the unique capability of antibodies to recognize particular antigens. Complementarity refers to the structural compatibility between an antibody and its antigen. Though these concepts are important in understanding antibody function, the "lock and key fit" best captures the nature of the binding mechanism itself.