Why are antibodies specific for certain pathogens?

• A. They are produced by memory B cells only.
• B. They can bind to any pathogen regardless of shape.
• C. Because their antigen binding site is complementary to the shape of an antigen.
• D. They change shape to fit every antigen.

Answer: (C)

Antibodies are specific because the binding site is complementary to the shape of a particular antigen. The region that binds—the variable parts of the heavy and light chains—forms a paratope that fits a specific epitope on that antigen. When the epitope matches, non-covalent interactions hold the antibody to the antigen, creating a tight, selective fit. This specificity comes from genetic rearrangements that generate a diverse repertoire, so each antibody is tailored to recognize a particular molecular shape on pathogens. Antibodies aren’t produced only by memory B cells; plasma cells secrete them after activation. They don’t bind every pathogen or freely change to fit any antigen—the binding site is specialized for a limited set of shapes.