The differences between active immunity and passive immunity and how they work. Active immunity, which involves the production of memory cells by the body, is triggered by exposure to a pathogen or a vaccine. In contrast, passive immunity, which only provides antibodies, is temporary and does not involve memory cells. The sources also discuss the key aspects of adaptive immunity, including the roles of B cells and T cells in producing antibodies and destroying infected cells. The sources further explain the important concept of antigens, which trigger the immune response, and their characteristics, such as epitopes and haptens. Finally, the sources detail the various functions of antibodies, which include neutralization, opsonization, agglutination, complement activation, and antibody-dependent cell-mediated cytotoxicity (ADCC).