Final answer:
Antibodies produced by plasma cells bind to antigens and signal for the destruction of the pathogen by macrophages, playing a vital role in the humoral immune response.
Step-by-step explanation:
The correct statement about the actions of antibodies in the immune response is: antibodies bind to antigens and mark the pathogen for destruction by macrophages. Antibodies, or immunoglobulins, are produced by plasma cells which are differentiated from B cells upon activation by an antigen. These antibodies are critical in the humoral immune response, targeting pathogens in the blood and lymph. Once an antibody binds to its specific antigen on a pathogen, it effectively marks that pathogen for phagocytosis by immune cells such as macrophages.
Helper T cells play a crucial role by releasing cytokines that help B cells multiply and differentiate into plasma cells. It's important to note that antibodies cannot directly target viruses and bacteria that are reproducing inside body cells; that is the function of cell-mediated immunity involving T cells, particularly killer T cells. Also, antibodies do not activate helper T cells or produce killer T cells; that is a role fulfilled by other aspects of the immune system.