In both innate and adaptive immune systems, they are:

• A. cell-mediated only
• B. humoral only
• C. cell-mediated and humoral components
• D. neither

Answer: (C)

Both innate and adaptive immunity involve two broad types of responses: cell-mediated actions carried out by immune cells and humoral actions carried out by soluble factors in body fluids. In the innate system, cell-mediated components include phagocytes like neutrophils and macrophages and natural killer cells, while humoral components include the complement system and other soluble mediators that help opsonize or destroy pathogens. In the adaptive system, cell-mediated immunity is driven by T cells that coordinate responses and kill infected cells, and humoral immunity is driven by B cells producing antibodies. Because each system employs both cell-based effects and soluble, fluid-phase effects, the statement that they are both cell-mediated and humoral components is the best description. The other options are too narrow, focusing on just one arm or implying neither arm is present.