The immune system is the body’s natural way to protect itself from illness and infection. When bacteria, viruses or other potentially harmful organisms enter the body, the immune system takes action. Part of this process is inflammation, which helps start the healing process. A fever or a red, swollen area around a cut are types of inflammation. In people with autoimmune diseases, the immune system mistakenly attacks healthy tissue the way it would normally fight off bacteria, viruses or other invaders. Similarly, chronic inflammation that targets healthy tissue is an autoinflammatory disease.