What is the name for a protein that binds or inactivates a specific antigen?

The correct answer is "antibody" because antibodies are specialized proteins produced by the immune system in response to the presence of antigens, which are foreign substances that can provoke an immune response. Antibodies recognize and bind to specific antigens, effectively neutralizing them or marking them for destruction by other immune cells. This binding action is crucial in the immune response, as it allows the body to identify and eliminate pathogens such as bacteria and viruses.

In contrast, the other terms do not fulfill the specific role of binding to or inactivating antigens. An antigen is the substance that can trigger an immune response, while an artifact refers to any unintended alteration or feature introduced during a process (such as in laboratory studies). An anticoagulant is a substance that prevents blood clotting, which is unrelated to the binding or inactivation of antigens. Therefore, "antibody" is the only term that accurately describes the protein function in the context of antigen interaction.