Immune disorders immune diseases arise when your immune system thinks that one or more of your body’s normal cells is actually a harmful or foreign substance and attacks it, causing inflammation and tissue damage. the cause of most autoimmune diseases is unknown, but researchers believe there may be an inherited predisposition. autoimmune disorders are usually difficult to diagnose, as they can lead to highly variable symptoms and those can change over time as well. signs and symptoms can also be slow to develop and so can be misleading during a diagnosis. one sign of possibly having an immunodeficiency is susceptibility to infections, or having infections that are occurring more frequently, lasting longer, or harder to treat. autoimmune disorders are grouped into two categories; systemic and localized. localized disorders attack only a single organ or type of tissue, whereas systemic disorders affect many organs or types of tissues. however, once enough damage has been done in a localized area, the disorder can start effecting other tissues or organs and can become a more systemic disorder.