What is the primary function of the spleen in relation to the immune system?

The primary function of the spleen in relation to the immune system is to filter blood and aid in responding to blood-borne pathogens. The spleen plays a crucial role in the immune response by identifying and responding to pathogens, such as bacteria and viruses, that are present in the bloodstream. It contains specialized areas of immune cells that can recognize foreign invaders and initiate an immune response, effectively acting as a blood filter.

Within the spleen, red pulp and white pulp perform distinct functions; the red pulp filters out old or damaged red blood cells, while the white pulp is rich in lymphocytes and plays a central role in monitoring and responding to infections. This structure allows the spleen to effectively capture and respond to blood-borne pathogens, making it an integral part of the immune system's defense mechanisms.

The other options do not accurately reflect the primary functions of the spleen. While it does play various roles in the body, such as participating in blood cell regulation, it does not produce hormones for growth or synthesize antibodies exclusively, nor does it primarily function as a nutrient storage organ.