What role does the spleen play in the immune system?

The spleen plays a crucial role in the immune system by filtering blood and responding to pathogens. While it does participate in the degradation of old and damaged white blood cells, its primary function related to immunity is to help in the removal of these cells to maintain a healthy population of white blood cells in the body.

Additionally, the spleen contains lymphoid tissue that produces immune responses against blood-borne pathogens, which emphasizes its role in defending the body against infections. It acts as a reservoir for immune cells, allowing them to proliferate and respond effectively when the body encounters foreign antigens.

The other options relate to functions that are not primarily associated with the spleen. For instance, the production of red blood cells typically occurs in the bone marrow, storage of platelets is a function related to the blood's systemic storage rather than the spleen’s main role, and filtering toxins from blood is generally a function fulfilled more by the liver and kidneys. Thus, the correct answer highlights the spleen's involvement in the immune response through the management and degradation of white blood cells.