<P> Some infections, such as Campylobacter jejuni, have antigens that are similar (but not identical) to our own self - molecules . In this case, a normal immune response to C. jejuni can result in the production of antibodies that also react to a lesser degree with receptors on skeletal muscle (i.e., Myasthenia gravis). A major understanding of the underlying pathophysiology of autoimmune diseases has been the application of genome wide association scans that have identified a degree of genetic sharing among the autoimmune diseases . </P> <P> Autoimmunity, on the other hand, is the presence of self - reactive immune response (e.g., auto - antibodies, self - reactive T - cells), with or without damage or pathology resulting from it . This may be restricted to certain organs (e.g. in autoimmune thyroiditis) or involve a particular tissue in different places (e.g. Goodpasture's disease which may affect the basement membrane in both the lung and the kidney). </P> <P> There are many theories as to how an autoimmune disease state arises . Some common ones are listed below . </P> <P> Although it is possible for a potential autoantigen to be geographically sequestered in an immune privileged site within the body (e.g. the eye), mechanisms exist to express even these antigens in a tolerogenic fashion to the immune system . However, it is impossible to induce tolerance (immune unresponsiveness) to all aspects of an autoantigen . This is because under normal physiologic conditions some regions of a self - antigen are not expressed at a sufficient level to induce tolerance . These poorly displayed areas of an antigen are called "cryptic determinants ." The immune system maintains a high - affinity repertoire to the cryptic self because the presentation of these determinants was insufficient to induce strong tolerance . </P>

Why are allergies not classified as autoimmune diseases