In the context of autoimmunity: (A) define molecular mimicry; and (B) provide an example
What will be an ideal response?
A. Molecular mimicry refers to the phenomenon in which a pathogen expresses an antigen that bears a chemical similarity to a host-cell antigen. Once pathogen-specific antibodies or effector T cells are generated, they have the potential to cross-react with self antigen.
B. An autoimmune disease involving molecular mimicry is rheumatic fever. Infection with Streptococcus pyogenes (for example ‘strep throat') results in the production of antibodies specific for the bacterial cell-wall proteins. These antibodies cross-react with chemically similar (but not identical) self antigen expressed on heart tissue. This is followed by complement activation and the production of inflammatory mediators, which cause damage to heart tissue and valves and the formation of scar tissue, which can lead to cardiovascular complications later in life. This type of immunological aftermath can be avoided if antibiotics are administered early during infection.
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