Which of the following is true of antibodies?

• A. They are immunoglobulins.
• B. They are enzymes.
• C. They bind nonspecifically to antigens.
• D. They deactivate the complement system.

Answer: (A)

Antibodies are immunoglobulins produced by B cells as part of the adaptive immune response. They are Y-shaped proteins with unique antigen-binding sites at the tips of the arms, designed to recognize a specific epitope on an antigen. This specificity is what makes antibodies effective at targeting particular pathogens or foreign substances, rather than binding something nonspecifically. They are not enzymes and do not normally catalyze chemical reactions. They can help activate the complement system when bound to an antigen, but they do not deactivate it. So the statement that best describes antibodies is that they are immunoglobulins.