Which of the following best describes an antibody?

An antibody is best described as a protein that triggers immune response. Antibodies are specialized proteins produced by the immune system, specifically by B cells. Their primary role is to identify and neutralize pathogens such as bacteria and viruses. When an antibody binds to its specific antigen (the harmful substance it targets), it helps the immune system to mark the pathogen for destruction or neutralization.

This function is crucial in protecting the body from infections and diseases. Antibodies can also facilitate other immune responses by recruiting other immune cells to help eliminate the threat. In contrast, the other options refer to different biological functions: harmful chemical detection, metabolic regulation, and nutrient absorption are not the roles of antibodies.