D- by injecting a weakened or dead pathogens, immune response is triggered. Phagocytes engulf pathogens and display their antigens to trigger T cells which help activate B cells. B cells divide into plasma cells which produce the correct antibody to fight the disease and memory T and B cells are produced. If the body is infected again the antigen will be recognised and memory B and T cells will produce antibodies meaning the immune response is quicker and the person will not show symptoms