19- Immunity to Bacteria and Fungi

Question 1

During the infection process when the pathogen proliferates, how does the host defense mechanism respond?

Answer 1

Phagocytosis
Complement-mediated lysis and localized inflammatory response

Question 2

During the infection process when the pathogen attaches to host cells, how does the host defense mechanism respond?

Answer 2

Blockage of attachment by secretory IgA antibodies

Question 3

During the infection process when the pathogen invades host TISSUES, how does the host defense mechanism respond?

Answer 3

Antibody-mediated agglutination

Question 4

During the infection process when there is toxin-induced damage to host cells, how does the host defense mechanism respond?

Answer 4

Neutralization of toxin by antibody

Question 5

How does TH17 play a role in immunity to extracellular bacteria like R. equi and fungal pathogens

Answer 5

TH17 cells trigger inflammation by releasing cytokines (IL-17, IL-21, IL-22) which protect against extracellular bacteria like R. equi and fungal pathogens

Question 6

What is the importance of vitamin D in immunity to mycobacteria?

Answer 6

Vitamin D receptors are up-regulated on the activated macrophages which leads to up-regulation of Vitamin D hydroxylase and increased up-regulation of Cathelicidins which leads to bacterial killing
- Cathelicidins are anti-microbial peptides

Question 7

What are the 5 basic mechanisms of adaptive immunity to bacteria

Answer 7

1) Neutralization of toxins or enzymes by antibodies
2) Killing of bacteria by the classical complement pathway
3) Opsonization of bacteria by antibodies and complement, resulting in their phagocytosis and destruction
4) Destruction of intracellular bacteria by activated macrophages
5) Killing of bacteria by CTLs and NK cells

Question 8

Explain the immune response to toxigenic bacteria

Answer 8

the immune response stops the invading bacteria as well as neutralizes the toxin
- neutralization occurs when antibodies prevent the toxin from binding to its receptor on a target cell

Question 9

Explain the immune response to invasive bacteria

Answer 9

Antibodies generated against capsular antigens neutralize the antiphagocytic property of bacteria capsules, thus permitting their destruction of phagocytic cells

Question 10

Explain the immune response to intracellular bacteria

Answer 10

Intracellular bacteria grow in macrophages. Protection from these bacteria is mediated by M1 macrophages (classically activated macrophages). Cell-mediated responses are required to control intracellular bacteria since only activated macrophages can prevent their growth. This requires Th1 and IFN

Question 11

Give an example of an inappropriate TH response that leads to insufficient immunity against an intracellular bacterium

Answer 11

If an animal mounts an inappropriate TH2 response, cell-mediated immunity fails to develop, M2 macrophages are generated, and chronic progressive disease may result. If there are no M1 macrophages and only increased M2 macrophages (clean-up), no pathogens will be killed, M2 just chase them around and try to clean up
- example is Johne’s disease

Question 12

Explain the importance of IL-23/ IL-17 axis in immunity to fungi

Answer 12

Neutrophils are activated by the IL-23/IL-17 axis during fungal infections- this activates the adaptive immune response
Both TH1 and TH17 responses are important in cellular immunity to fungi by enhancing pro-inflammatory reactions