I. BACTERIAL PATHOGENESIS

C. VIRULENCE FACTORS THAT DAMAGE THE HOST

3. Inducing Autoimmune Responses

Fundamental Statements for this Learning Object:

1. Autoimmunity is when the body's immune defenses mistakenly attack the body and sometimes certain bacteria can serve as a trigger for this response.
2. One way bacteria can trigger autoimmunity by stimulating the production of cross-reacting antibodies. These are antibodies made in response to bacterial antigens then accidently cross-react with and destroy host cells to which they have bound. An example is rheumatic fever following Streptococcus pyogenes infection.
3. Another way autoimmunity can be triggered by certain bacteria is by stimulating the production of soluble antigen-antibody (immune) complexes. These immune complexes can lodge in filtering units such as the kidneys where they activate the complement pathway and trigger an inflammatory response then destroys kidney tissues. An example of this is acute glomerulonephritis that sometimes following infection by Streptococcus pyogenes.

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 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 induce autoimmunity.

The Ability to Induce Autoimmune Responses

Autoimmunity (def) is when the body's immune defenses mistakenly attack the body. In certain cases, 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.

GIF animation showing opsonization of cells during Type-II hypersensitivity. by Gary E. Kaiser, Ph.D. Professor of Microbiology, The Community College of Baltimore County, Catonsville Campus This work is licensed under a Creative Commons Attribution 4.0 International License. Based on a work The Grapes of Staph at https://cwoer.ccbcmd.edu/science/microbiology/index_gos.html. Last updated: August, 2019 Please send comments and inquiries to Dr. Gary Kaiser

GIF animation showing MAC lysis of cells during Type-II hypersensitivity. by Gary E. Kaiser, Ph.D. Professor of Microbiology, The Community College of Baltimore County, Catonsville Campus This work is licensed under a Creative Commons Attribution 4.0 International License. Based on a work The Grapes of Staph at https://cwoer.ccbcmd.edu/science/microbiology/index_gos.html. Last updated: August, 2019 Please send comments and inquiries to Dr. Gary Kaiser

html5 animation showing ADCC by NK cells by Gary E. Kaiser, Ph.D. Professor of Microbiology, The Community College of Baltimore County, Catonsville Campus This work is licensed under a Creative Commons Attribution 4.0 International License. Based on a work The Grapes of Staph at https://cwoer.ccbcmd.edu/science/microbiology/index_gos.html. Last updated: August, 2019 Please send comments and inquiries to Dr. Gary Kaiser

html5 animation showing ADCC apoptosis by NK cells by Gary E. Kaiser, Ph.D. Professor of Microbiology, The Community College of Baltimore County, Catonsville Campus This work is licensed under a Creative Commons Attribution 4.0 International License. Based on a work The Grapes of Staph at https://cwoer.ccbcmd.edu/science/microbiology/index_gos.html. Last updated: August, 2019 Please send comments and inquiries to Dr. Gary Kaiser

For More Information: Type-II Hypersensitivities from Unit 6

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).

GIF animation showing inflammation and tissue death during Type-III hypersensitivity. by Gary E. Kaiser, Ph.D. Professor of Microbiology, The Community College of Baltimore County, Catonsville Campus This work is licensed under a Creative Commons Attribution 4.0 International License. Based on a work The Grapes of Staph at https://cwoer.ccbcmd.edu/science/microbiology/index_gos.html. Last updated: August, 2019 Please send comments and inquiries to Dr. Gary Kaiser

 

For More Information: Type-III Hypersensitivities from Unit 6

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 destructive skin lesion) following infection by Treponema pallidum (inf).

 

TPS Question

Concept map for the Ability to Induce Autoimmune Responses.

Medscape article on infections associated with organisms mentioned in this Learning Object. Registration to access this website is free. Streptococcus pyogenes Treponema pallidum Leptospira Borrelia burgdorferi

Autoimmunity will be discussed in greater detail under Hypersensitivities in Unit 6.

• QUIZ YOURSELF ON THIS SECTION

Gary E. Kaiser, Ph.D.
Professor of Microbiology
The Community College of Baltimore County, Catonsville Campus
This work is licensed under a Creative Commons Attribution 4.0 International License.
Based on a work The Grapes of Staph at https://cwoer.ccbcmd.edu/science/microbiology/index_gos.html.