What role do the lymph nodes play in the immune system?

The lymph nodes play a critical role in the immune system primarily by filtering lymph fluid. As lymph fluid circulates throughout the body, it collects waste products, pathogens, and cellular debris. When lymph fluid passes through the lymph nodes, they serve as a checkpoint, where immune cells, such as lymphocytes, can detect and respond to any foreign substances present in the fluid. This filtering process is essential for the activation of the immune response, helping to protect the body from infections and diseases.

Lymph nodes also act as sites for the proliferation of immune cells, which can then be dispatched to locations in the body where they are needed to mount an immune response. This is why lymph nodes often swell during infections, as they are busy producing more immune cells to combat the pathogens.

The other options provided do not accurately reflect the function of lymph nodes. They do not store hormones, produce red blood cells, or play a direct role in digestion. Thus, the role of lymph nodes in filtering lymph fluid is essential for maintaining a healthy immune system.