ABSTRACT
The function of the immune system is to protect the host against foreign organisms (virus, bacteria, fungus), “foreign cells” (neoplasm), and other foreign substances. Its importance is evidenced by the seriousness of immunodeficiency:
patients with this disorder are prone to be affected by infection and tumors. Immunodeficiency can be congenital or acquired; the latter is also known as AIDS (acquired immunodeficiency syndrome).
