The immune system is the key unit which protects the body against diseases. A healthy immune system detects pathogens from viruses to parasitic worms, and knows the difference between foreign bodies and the body's own healthy tissue. There are various types of immunity; active, passive, cellular, humoral and herd immunity. The immune system in vertebrates is more sophisticated and consists of many types of proteins, cells, organs and tissues. Among these many parts, located in the left upper abdomen, underneath the left rib cage in humans, is an organ known as the spleen. This organ is present virtually in all vertebrate animals. The spleen in humans is a soft organ, and of the size of a fist. It is dark purple in appearance, and 12 cm length, 7 cm height and 4 cm thickness are the average statistics of this organ. The spleen can weigh from 100 to 205 g, depending on the age and health of an adult. Although the spleen is not necessary for human survival, its absence would make us more vulnerable to infections. Working of the Spleen Spleen function in immune system is incomplete with its two distinct components; the red pulp and the white pulp. The red one covers almost 76-79% of the organ, while the rest comprises the white pulp. What does the red pulp do? The red pulp is responsible for the filtration function of the spleen and acts as a reservoir for the blood. This filtration process of the red pulp involves removal of old or damaged red blood cells from the circulation. The damaged blood cells are destroyed with the help of macrophages. Because of its filtration process, the red pulp also acts as a reservoir that supplies blood in case of any emergency which may cause severe blood loss. What does the white pulp do? The immunological function of spleen in the human body is looked after by the white pulp which consists of aggregates of lymphoid tissue. It plays its role by identifying antigens and producing antibodies. It is also assigned the job of making and maturing immune cells and blood cells. Its main purpose is to mount an immunological response to antigens within the blood, and this is what plays a vital role in fighting infections. Spleen has another important function and that is to produce red blood cells and white blood cells. However, the spleen makes RBCs for a temporary period that is during the early development of the uterus. But as birth approaches, this organ gradually resigns from this job, and the production of red blood cells is eventually taken over by the bone marrow. For the rest of the life, the organ makes white blood cells to fight infection as a part of the lymphatic system. Factors Which May Interfere with Functions of the Spleen Enlargement of the spleen is one of the most critical spleen problems. Diseases such as mononucleosis, liver cirrhosis, lymphoma, leukemia, and polycythemia vera has spleen enlargement as one of their severe complications. Spleen enlargement raises concerns as it increases the risk of developing infections. This is due to the fact that when the organ enlarges in its size, it tends to trap more than required red and white blood cells and platelets at an abnormal rate. This causes a lack of the amount of blood cells in the blood stream which are required to protect the body against infections. This disorder of the spleen is cyclic in nature. The more the organ traps the blood cells, the more it increases in size and eventually it causes a major turmoil in its function. At a severe stage, the spleen may run out of its own blood supply, and may cease to function or die. Another medical disorder known as sickle cell anemia causes the spleen to shrink and become non-functional. To sum up, knowing about the different causes and symptoms of any disorder of the spleen is as important as being aware of its function. The treatment is focused on addressing the underlying cause of the disorder through non-invasive procedures. In some cases, surgical removal of the spleen (splenectomy) may also be necessary depending on the severity of the case. Splenectomy is usually done using laparoscopy so that the doctor is required to make small incisions at the site of operation. And once this organ is removed, the patient is recommended to take important vaccines or other medications to keep himself/herself from contracting any infection.