Question: what are the major organs and functions of the immune system?
Answer: Lymphoid organs. The immune system is made up of organs that control the production and maturation of certain defense cells, the lymphocytes. ... 
Bone marrow. ... 
Thymus. ... 
Lymph nodes. ... 
Spleen. ... 
Tonsils. ... 
Lymphatic tissue in the bowel and in other mucous membranes in the body. ... 
Sources.