Which type of immunity is mediated by antibodies?

Humoral immunity is specifically characterized by the production of antibodies that target pathogens such as bacteria and viruses. This type of immunity involves B cells, a subset of lymphocytes, which differentiate into plasma cells that produce antibodies. These antibodies circulate in the bloodstream and lymphatic system, binding to antigens on pathogens to neutralize them or mark them for destruction by other immune cells.

In contrast, cell-mediated immunity relies on T cells to directly kill infected host cells or coordinate the immune response, rather than using antibodies. Innate immunity refers to the body's first line of defense, which acts immediately or within hours of an antigen’s appearance in the body and does not involve memory or specificity. Passive immunity, on the other hand, involves the transfer of antibodies from one individual to another, providing temporary protection without the host's immune system being actively involved in producing those antibodies.

Thus, the characteristic feature of humoral immunity is the production and action of antibodies, making it the correct choice.