Everyone knows the immune system works to fight sickness and disease. But what happens if it's not working properly? What happens if our system becomes too offensive, or if it starts fighting itself?
The immune system is an impressive defensive structure consisting of white blood cells or leukocytes, and the proteins, tissues, and organs that store, produce, or assist them. Leukocytes come in two types: phagocytes, which are the initial destroyers of foreign organisms, and lymphocytes, which remember previous invaders (antigens) and defend against them. A common phagocyte is neutrophil, which fights bacteria. Raised levels of neutrophil in a blood test indicate to doctors that there may be bacterial infection in the body. Lymphocytes can be either B cells, which find antigens, and T cells, which are sent by the B cells to destroy the antigens.
The immune defense system can have problems in many different ways, even given the relative simplicity of the system. An immunodeficiency is when part of the immune system is missing or might be malfunctioning. One example is when the body has too little IgA, which is an immunoglobulin found in most bodily fluids. If there isn't enough IgA produced, antigens coming into the body will cause allergies or may be subject to more colds and respiratory infections.
Severe combined immunodeficiency (SCID) is a condition where the body doesn't produce B cells and T cells, and thus has virtually no defense against any incoming antigens. AIDS, or acquired immunodeficiency syndrome, is caused by the HIV virus, which attacks T-helper cells and disables the system from defending against antigens that would be harmless otherwise. There are also medications that are designed to suppress the defense system for organ transplants. All of these result in a weak immune system.
Sometimes the immune system attacks the body as if it was an invader. Lupus is a condition where the muscles and joints are attacked. Rheumatoid arthritis is similar to Lupus, however it primarily attacks the knee, hand, and foot joints. Scleroderma affects the skin and internal organs.