The spleen is an organ found in almost all vertebrate animals. It mainly acts as a filter for purifying the blood, removing microbes and worn out or damaged red blood cells. It is also an important organ in the immune system, producing the white blood cells that fight infection and synthesize antibodies.
Although the spleen is important for many functions in the body, the spleen is not vital to survival and it is possible to live without a spleen. Without the spleen, other organs in the body (particularly the liver) adapt and increase their ability to fight infection and remove redundant red blood cells.