FUNCTIONS OF THE IMMUNE SYSTEM

Under normal circumstances the immune system responds to foreign organism by production of antibodies and the stimulation of antigen-specific lymphocytes, leading to killing of the organism and neutralization of their toxic product (toxins). A major function of the immune system is surveillance of the cells of the body to ensure that they are not abnormal. Cell infected with viruses, malignant cell, or cells from another individual of the same species have protein markers on their outer membrane that act as a signal to the immune system to destroy them. The system to which these proteins belong is called the major histocompatibility complex (MHC) .

Immune responses are not always beneficial. They can contribute directly to pathological processes during infections and autoimmunity. The term hypersensitive or allergy are used when immune reaction produce tissue damage and harm the host; such reactions to an other wise harmless foreign substances may have severe effect and even lead to anaphylactic shock and death. In some cases for reasons that are not clear, normal cell may be wrongly identified as foreign or abnormal.

The immune system may develop antibodies and activate lymphocytes against them, producing autoimmune disease including systemic Lupus erythematosus, Myasthenia Gravis, diabetes and graves’ disease. Immune system also can develop by giving a vaccine to human or to animals.