Final answer:
An antigen is a foreign or "non-self" macromolecule that triggers an immune response in the body. It can be any substance that binds to specific receptors on immune cells. The immune system can differentiate between self-antigens and non-self antigens and only responds to the latter. The option (E) is correct.
Step-by-step explanation:
An antigen is a foreign or "non-self" macromolecule that reacts with cells of the immune system. It can be any substance that is capable of binding to specific receptors on immune cells and triggering an immune response. An antigen may be a protein, carbohydrate, or other macromolecule.
Not all antigens will provoke a response, as the immune system can distinguish between self-antigens and non-self antigens. Therefore, option (E) is correct.
This question is not complete, Here I am attaching the complete question:
Which of the following best defines an antigen?
(A) Any protein or carbohydrate that enters the body
(B) Any substance that can combine with T or B cells
(C) A substance that binds to a specific site on the Fab fragments of antibodies
(D) A simple substance that is not immunogenic itself but can react with a specific antibody
(E) Any substance that can evoke an immune response