Which immune response is NOT a part of the adaptive defenses?

Natural killer cell activity is associated with the innate immune response rather than the adaptive immune response. The innate immune system acts as the first line of defense, responding quickly to a wide range of pathogens without the need for prior exposure or sensitization. Natural killer cells are part of this system and are critical for identifying and destroying infected or cancerous cells without requiring antibodies or prior learning about a specific pathogen.

In contrast, antibody-mediated defense involves the production of antibodies by B cells, which is a hallmark of the adaptive immune system. Similarly, cell-mediated defense invokes T cells to recognize and eliminate infected host cells, and B-cell activation is the process through which B cells are stimulated to produce antibodies following exposure to an antigen. All of these components—antibody-mediated defense, cell-mediated defense, and B-cell activation—reflect the specificity and memory associated with adaptive immunity, which is why they differ fundamentally from the function of natural killer cells.