Under normal conditions, an immune response cannot be triggered against the cells of one's own body. In certain cases, however, immune cells make a mistake and attack the very cells that they are meant to protect. This can lead to a variety of autoimmune diseases. They encompass a broad category of related diseases in which the person's immune system attacks his or her own tissue.
Some lymphocytes are capable of reacting against self, resulting in an autoimmune reaction.
Ordinarily these lymphocytes are suppressed. Autoimmune processes can have various results, for example, slow destruction of a specific type of cells or tissue, stimulation of an organ into excessive growth, or interference in its function. Some autoimmune diseases fall between the two types. Patients may experience several organ-specific diseases at the same time. There is, however little overlap between the two ends of the spectrum.