The spleen works as a recycling plant; the other organ with a similar function is the Liver. Spleen is the organ composed of lymphatic tissue which filters blood and produces white blood cells. The spleen plays multiple supporting roles in the body; it acts as a filter for blood as part of the immune system. Old red blood cells are recycled in the spleen, and platelets and white blood cells are stored there. The spleen also helps fight certain kinds of bacteria that cause pneumonia and meningitis.