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2) Tolerance and autoimmunity
Briefly explain the following mechanisms for the development of autoimmunity, and for each of them give an
example.
a) Viral infection……………
The immune response against a virus may cross-react with normal cellular antigens
(molecular mimicry).
Example: myelin basic protein and peptides from viruses such as measles virus, influenza,
adenovirus, hepatitis B, Epstein-Barr
b) Tissue damage…………….
If normally sequestered antigens are exposed, self-reactive T cells may be stimulated.
Example:
Tissue lesion following an accident or a viral or bacterial infection (release of lens
protein after eye damage or of heart muscle antigens after myocardial infarction)
c) Polyclonal B cell activation……….
Some viruses and bacteria can induce nonspecific polyclonal B cell activation; B cells reactive
to self antigens can be activated, with production of autoantibodies
Example: Gram-negative bacteria, cytomegalovirus and Epstein-Barr virus (EBV)
d) Increased expression of class II MHC molecules…….
Inappropriate antigen presentation may stimulate self-reactive T cells
Example: increased expression of class II MHC molecules has been found on pancreatic beta
cells of patients with insulin-dependent diabetes and on thyroid cells from patients with
Grave’s disease