JIA Causes and the Role of the Immune System

By Robyn Abree

Although the exact cause of juvenile idiopathic arthritis (JIA) is unknown, doctors know that the immune system plays an important role.  Researchers are trying to better understand that role, which may be different for different subtypes of JIA.  There are two main theories:

1. JIA is an autoimmune disease.  - Autoimmune diseases result from an error in the acquired or adaptive immune system. This complex arm of the immune system develops throughout life and learns to recognize harmful foreign invaders over time. Once a threat has been identified, the adaptive immune system releases proteins called antibodies to help fight it. In some types of JIA, this process goes awry, and the adaptive immune system mistakes the body’s cells for foreign invaders. As a result, antibodies attach to the body’s own tissue instead (chiefly joint tissue), signaling the immune system to attack them. 
    
2. JIA is an autoinflammatory disease. - Many researchers believe that at least one type of JIA – systemic JIA (SJIA) – is an auto-inflammatory disease.  Auto-inflammatory diseases result from an error in the innate immune system. Unlike the adaptive immune system, which develops over time, the innate immune system is present at birth. It’s also the body’s first line of defense against infection. The quick inflammatory response that happens when you cut yourself (e.g. swelling, redness, warmth) is an example of the innate immune system at work. As such, autoinflammatory diseases often trigger episodes of intense inflammation for unknown reasons, usually causing high spiking fevers and rash. 

JIA Causes and Triggers 
Some researchers believe that JIA may share some aspects of both autoimmune and auto-inflammatory diseases. Although no one knows for sure what causes the immune system to function improperly and cause JIA, the disease is believed to result from genetic and environmental factors. In other words, children may inherit genes that put them at risk of JIA, but something in their environment, like catching a virus, may set the disease in motion. To date, more than a dozen genes have been identified as strongly associated with JIA. 

Regardless of its cause, uncontrolled inflammation can cause damage to the joints and other tissues. Prompt treatment is key to managing the disease and preventing complications and possible comorbidities.