Final answer:
The answer is 1. Humoral; antigen, where an antigen binds to the receptor of a B or T cell, leading to the activation of humoral immunity, a key component within the larger adaptive immune system.
Step-by-step explanation:
In antibody-mediated, or humoral immunity, an antigen selects and then binds a specific B or T cell at its receptor. The correct option is: 1. Humoral; antigen. This is because humoral immunity involves the production of antibodies by B cells, which are key to combating pathogens located in extracellular spaces. When a foreign antigen binds to a B cell's receptor, the B cell becomes activated, proliferating and differentiating into plasma cells that secrete specific antibodies against the pathogen. These antibodies can neutralize the pathogen, mark it for destruction by other cells, or interfere with its ability to infect host cells. Humoral immunity is part of the larger adaptive immune system that also includes cell-mediated immunity, which is carried out by T cells against intracellular pathogens. The adaptive immune system is characterized by specificity and memory, providing long-term protection against reinfection by the same pathogen.