Organs of the Immune System: The Spleen


Among organs that contribute to our immune response, there are two categories: primary lymphoid organs and secondary lymphoid organs.

The spleen is a secondary lymphoid organ.

The Spleen's Jobs

Your spleen is found about halfway up your torso in the left abdominal cavity. In adults, it measures about five inches in length, three in width, and as many as 11 inches thick. In healthy folks, it weighs about 6 ounces, but when disorders emerge, it can balloon up to 4 pounds or more.

The chief jobs of the spleen are to filter from the blood damaged red blood cells and platelets, as well as any existent blood-borne antigens, which it traps. In the process it produces B-lymphocytes, all in the process of helping the immune system.

The spleen isn't supplied by vessels of the lymph variety; rather, it receives blood, with antigens and lymphocytes, through the splenic artery and it empties out the splenic vein. According to the sixth edition of Kuby's Immunology, "more recirculating lymphocytes pass daily through the spleen than through all the lymph nodes combined."

The Spleen in Lymphoma

The splenic artery takes lymphocytes and antigens into the spleen and ditches them near an area known as the marginal zone where they meet lymphocytes and macrophages. When lymphocytes in the marginal zone, for whatever reason, become cancerous, then the diagnosis is that of marginal zone lymphoma.

A non-Hodgkin's lymphoma of B-cell origin, there are three main subtypes of marginal zone lymphoma, with just one directly affecting the spleen: Splenic marginal zone lymphoma (SMZL). This disease, which is extraordinarily rare, accounts for less than one percent of lymphomas annually, is highly responsive to treatment and has a five-year survival ("cure") rate of around 93 percent.

Splenic involvement is not uncommon in Hodgkin's lymphoma; an estimated 45 percent or more of cases are found to involve the spleen.

In both cases the spleen acts much like a cancerous lymph node and enlarges as cancerous B-lymphocytes collect there.

Losing Your Spleen: Splenectomy

Sometimes - due to lymphoma, or due to other disorders or even due to trauma - the spleen needs to be surgically removed. When this is done, it is called a splenectomy.

A splenectomy is a survivable experience (talk show host Jay Leno wrote about losing his spleen as a child in Leading With My Chin), but the consequences of not having a spleen are different depending on your age. Younger people who lose their spleen will likely have problems over time with bacterial sepsis caused by the likes of Streptococcus pheumoniae and other dangerous bacterium. Older folks won't have as many problems, but they will still be at increased risk of developing blood-borne bacterial infections.

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