Definition: The immune system is a collection of organs, cells and tissues that work together to protect your body from disease caused mostly by pathogens (bacteria, viruses, parasites and fungi). Some parts of the immune system are your tonsils, lymph nodes, appendix, spleen and thymus. In addition, specialized cells, called "white blood cells," patrol throughout your body looking for pathogens.
The immune system is very complex and plays a direct role in immunization, infectious diseases, allergies and autoimmune diseases (such as autoimmune hepatitis and rheumatoid arthritis). For people with viral hepatitis, the immune system is extremely active and is responsible for whether the disease will be acute, fulminant or chronic.
