I. BACTERIAL PATHOGENESIS
C. VIRULENCE FACTORS THAT DAMAGE THE HOST
3. Inducing Autoimmune Responses
The overall purpose of this Learning Object is:
1) to introduce how some bacteria cause harm by inducing autoimmune responses in the body; and
2) to introduce several medically important bacteria that may induce autoimmune responses.
LEARNING OBJECTIVES FOR THIS SECTION
In this section on Bacterial Pathogenesis we are looking at virulence factors that damage the host. Virulence factors that damage the host include:
1. The ability to produce cell wall components (Pathogen-Associated Molecular Patterns or PAMPS) that bind to host cells causing them to synthesize and secrete inflammatory cytokines and chemokines;
2. The ability to produce harmful exotoxins.
3. The ability to induce autoimmune responses.
We will now look at the ability of bacteria to produce harmful exotoxins.
The Ability to Induce Autoimmune Responses
Autoimmunity is when the body's immune defenses mistakenly attack the body and sometimes certain bacteria can serve as a trigger for this response.
One way bacteria can do this is by inducing the production of cross-reacting antibodies (def) and possibly auto-reactive cytotoxic T-lymphocytes or CTLs (def). These are antibodies and CTLs made in response to bacterial antigens (def) that accidently cross react with epitopes (def) on host cells. As a result, the antibodies and CTLs wind up destroying the host cells to which they have bound. Furthermore, when the antibodies activate the classical complement pathway (def), this further stimulates the inflammatory response resulting in more tissue damage. Rheumatic fever triggered by rheumatogenic strains of Streptococcus pyogenes (inf) is an example. Antibodies and CTLs stimulated by antigens of S. pyogenes cross-react with heart and joint tissues damaging the heart and joints.
Another way autoimmunity can be triggered by certain bacteria is by stimulating the production of soluble immune complexes. When high levels of circulating antibodies react with certain bacterial antigens, they form large amounts of immune complexes (antibodies bound to antigens). These immune complexes can lodge in filtering units such as the kidneys where they activate the complement pathway (def). The resulting inflammatory response then destroys kidney tissues. An example of this is acute glomerulonephritis that sometimes following infection by Streptococcus pyogenes (inf).
Two other possible examples of bacterial induced autoimmunity are chronic Lyme disease (arthritis, neurological abnormalities, and heart damage) following infection by Borrelia burgdorferi (inf), and tertiary syphilis (heart damage, neurological abnormalities, and distructive skin lesion) following infection by Treponema pallidum (inf).
E-Medicine article on infections associated with organisms mentioned in this Learning Object. Registration to access this website is free.
Autoimmunity will be disussed in greater detail under Hypersensitivies in Unit 5.
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Updated: Aug., 2012
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