The role of the spleen in the immune system is critical for filtering and regulating blood components. Located in the upper left abdomen, the spleen removes old or damaged red blood cells and helps recycle iron and other components. It also plays a key role in the immune response by producing and storing white blood cells, including lymphocytes, which are essential for fighting infections. By acting as a reservoir for blood and immune cells, the spleen contributes significantly to the body’s ability to respond to pathogens.