Abstract

The immune system recognizes and defends us against internal threats caused by invading organisms and pathogens. The innate immune system recognizes bacteria, fungi and other organisms, breaks them down, identifies a characteristic protein on them (an antigen) and attaches it to the surface of specific cells, which present it to the adaptive immune system for destruction. The adaptive or acquired immune system acts once then it is stimulated by the innate system. The adaptive immune response is initiated by specific interactions between antigen loaded, mature dendritic cells and naïve CD4⁺ T cells in the lymph nodes. The five families of immune cells are: phagocytes, granulocytes, natural killer (NK) cells, lymphocytic T-cells and lymphocytic B-cells. The four major classes of immune system mediators are chemotactic agents, cytokines, C-reactive protein and antibodies. A fifth class of immune network mediators comprises the small molecules, including neurotransmitters, such as L-DOPA and catecholamines. Risk factors for autoimmune diseases include exposure to man-made chemicals. Benlysta (belimumab) is approved for treating lupus erythematosus. AIDS is caused by the retrovirus HIV. Currently, a mixture, or cocktail of antiretroviral drugs is given in what is often called highly active antiretroviral therapy, or HAART. Microbes in the intestines and lungs (acquired from the environment) keep rare invariant natural killer immune cells from triggering autoimmune diseases.