What role do cilia play in the immune defense?

Cilia play a significant role in the immune defense by moving pathogens away from the body, particularly in the respiratory tract. They are small, hair-like structures that line the surfaces of certain cells, such as those in the respiratory system. When cilia beat in a coordinated manner, they create a wave-like motion that helps to propel mucus, along with any trapped pathogens, dirt, and particles, upward toward the throat. This action is crucial for clearing the airways and preventing pathogens from reaching the lungs, thereby contributing to the body's defense against infections.

The other options do not accurately describe the primary function of cilia in the immune system. While some cells do secrete antimicrobial substances and produce mucus, these activities are mainly the roles of different cell types, not cilia themselves. Furthermore, cilia do not play a role in nutrient absorption; that function is typically associated with microvilli found in the intestines. Thus, the movement of pathogens away from the body by cilia is the most appropriate answer in this context.