Which type of protein can act as an antibody?

Immunoglobulins, also known as antibodies, are specialized proteins produced by the immune system in response to foreign substances, such as pathogens or toxins. They play a crucial role in the body's defense mechanisms by identifying and neutralizing these invaders. Each immunoglobulin has a unique structure that allows it to bind specifically to a particular antigen, which is a foreign molecule that triggers an immune response. This binding can mark the pathogen for destruction by other immune cells or neutralize its harmful effects directly.

The effectiveness of immunoglobulins is central to the adaptive immune response, where they provide long-lasting protection and memory against previously encountered pathogens. Their ability to recognize and bind to specific antigens sets immunoglobulins apart from other types of proteins like enzymes, hormones, or cytokines, which serve different biological functions. Enzymes catalyze biochemical reactions, hormones regulate physiological processes, and cytokines act as signaling molecules that mediate immune responses, but none of these can function in the capacity of an antibody.