The immune system normally recognises and tolerates all of the body's own tissues. However, in some conditions the immune system reacts against 'self', resulting in autoimmune disease. The targets may be individual molecules found in a specific tissue, or antigens present in many tissues or in the extracellular matrix. Table 1 gives some examples of autoimmune diseases and the target antigens. An example of a tissue-specific autoimmune disease is Hashimoto's thyroiditis, in which lymphocytes recognise thyroglobulin and a thyroid peroxisome antigen (Figure 5).
Table 1 Autoimmune diseases
|Disease||Organ||Target antigens||Histological appearance|
|Destruction of thyroid follicles with severe inflammation|
|Goodpasture's syndrome||Kidney, lung||Basement membranes|
Damage to kidney glomerulus
and/or lung alveolae
|Myasthenia gravis||Skeletal muscle||Acetyl choline receptor||Degeneration of the motor endplate at nerve/ muscle junction|
|Desmosome proteins in keratinocytes||Separation of layers of epithelium|
|Diabetes - type I||Islets of Langerhans|
Pancreatic beta cells
Insulin , GAD (enzyme)
|Selective damage and loss of cells of pancreatic Islets with inflammation|
|Erosion of articular cartilage by fibrous, inflammatory tissue - pannus.|
|Systemic lupus erythematosus||Kidney, skin, CNS||DNA and intracellular antigens||Type-3 hypersensitivity reaction in kidney, damage to glomerulus|
The histological appearance of autoimmune disease depends on the nature of the immune response and the target organ. However a characteristic of many organ-specific diseases is that autoantibodies bind to the antigen within the tissue and recruit inflammatory cells. In this case, direct immunofluorescence microscopy can be used to identify the presence of antibodies, which goes a long way towards providing a diagnosis of the disease (Figure 6). It is also possible to detect autoantibodies in the blood of patients, using the same technique; the patient's serum is first incubated with normal tissue to allow any autoantibodies to bind, and these are then detected, by direct immunofluorescence or immunohistochemistry. Examination of the stained sections can determine not just whether there are autoantibodies in the serum, but also indicate what the target antigen might be, depending on where the autoantibodies are located in the cells.