Introduction to histopathology
Introduction to histopathology

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Introduction to histopathology

1.4 Autoimmunity

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

DiseaseOrganTarget antigensHistological appearance
Hashimoto's thyroiditisThyroid

Thyroglobulin

Thyroid peroxisomes

Destruction of thyroid follicles with severe inflammation
Goodpasture's syndromeKidney, lungBasement membranes

Damage to kidney glomerulus

and/or lung alveolae

Myasthenia gravisSkeletal muscleAcetyl choline receptorDegeneration of the motor endplate at nerve/ muscle junction
Pemphigus

Skin, mucosa

Desmosome proteins in keratinocytesSeparation of layers of epithelium
Diabetes - type IIslets of Langerhans

Pancreatic beta cells

Insulin , GAD (enzyme)

Selective damage and loss of cells of pancreatic Islets with inflammation
Rheumatoid arthritisJoint

IgG antibodies,

cartilage components.

Erosion of articular cartilage by fibrous, inflammatory tissue - pannus.
Systemic lupus erythematosusKidney, skin, CNSDNA and intracellular antigensType-3 hypersensitivity reaction in kidney, damage to glomerulus
Figure 5 Hashimoto's thyroiditis is an example of an autoimmune disease, in which the thyroid follicles are destroyed by an immune reaction against components of the thyroid, including thyroid peroxisomes and thyroglobulin. Scale bar = 50µm.

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.

Figure 6 Autoantibodies to Islets of Langerhans in the pancreas in type-1 diabetes may be demonstrated by immunofluorescence (Courtesy of Dr B. Dean)
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