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The avian immune system is the system of biological structures and cellular processes that protects birds from disease. The avian immune system resembles that of mammals since both evolved from a common reptilian ancestor and have inherited many commonalities. They have also developed a number of different strategies that are unique to birds. Most avian immunology research has been carried out on the domestic chicken, Gallus gallus domesticus. Birds have lymphoid tissues, B cells, T cells, cytokines and chemokines like many other animals. They can also have tumours, immune deficiency and autoimmune diseases.