First, read about inflammation.
To effectively eliminate invaders such as bacteria and viruses, the immune system must distinguish “foreign” from “self” using antigen/antibody recognition. This is called the antibody-mediation system. Antigens are proteins (the building blocks of cells) not native to the body. Certain white blood cells (WBCs) produce their own proteins called antibodies that bind to specific antigens, producing a larger complex. WBCs in charge of “clean up” sense and remove these complexes, thus eliminating antigens. Antibodies are also known as immunoglobulins. The terms IgA, IgD, IgE, IgG, and IgM refer to types of antibodies.
Autoimmune diseases occur when the body’s immune system makes an error creating antibodies, mistaking “self” for “foreign.” The body produces specific antibodies to foreign antigens in a many step process, the preliminary phases of which take place before birth. Infants start antibody formation at 6 months, as they encounter more of the environment. When the body mistakenly produces …..to its own tissues, chronic inflammation… and tissues can occur.
For example, in rheumatoid arthritis, the immune system mistakes joint-lining tissue (synovium) as foreign, and produces antibodies to it. Since WBCs continuously try to “clean up the complexes”, an ongoing cycle of destruction, followed by attempted repair, persists. How and why the immune system produces this error is unclear. Possibly, by coincidence, the self-antigen might be similar to a previously invading antigen (like that of a cold or flu). Alternatively, a trauma could break tissue and “present” self-antigen to the immune system. Cigarette smoking and genetics play roles here, but no one know exactly why these mistakes occur, and are increasing.