Antibodies are a protein that is produced by plasma cells. Plasma cells are also called effector B cells. B cells are B lymphocytes, and lymphocytes are white blood cells. For example, B lymphocytes in the body, when stimulated by a foreign substance, such as an injected hepatitis B vaccine, will transform and differentiate into plasma cells that produce a protein that specifically targets the hepatitis B virus. This stimulated hepatitis B virus acts as an antigen, and the protein produced by the plasma cells is called an antibody. When the hepatitis B virus enters the body again or is infected by someone else, the antibodies will immediately recognize it and respond to destroy the foreign hepatitis B virus and protect the body from hepatitis B. Antibodies are not always protective, but can sometimes be life-threatening. For example, a patient who is severely allergic to penicillin will not be allergic after the first exposure to penicillin, but will produce an antibody after the exposure, and when exposed to penicillin again, the antibody will play a bad role and can cause the patient to go into anaphylactic shock, and the patient’s life will be in danger if not rescued in time.