Lecture 27 Infectious Diseases (Stahelin)

Question 1

What is the normal defense mechanisms against pathogens

Answer 1

the normal defense against pathogens fall into two categories physical/chemical barriers and Innate/adaptive immunity
Physical and chemical barriers include
- enzymes in the mucus
- Skin (5.5 pH)
- mucosal membrane in the intestines
- antibacterial proteins and zinc in semen
- Stomach acid that has a high Ph which most bacteria cannot survive in.
Innate/adaptive barriers include
- cells can move to the site of injury to kill of bacteria

Question 2

what are the common routes of infection and how pathogens can break the normal defenses (e.g., skin and respiratory, intestinal and urogenital tracts).

Answer 2

Skin: Pathogens can enter by wounds and cuts on the skin. They can also produce enzymes that will break skin barriers
Respiratory Tract: Pathogens may have optimized protein structures that are exposed on their outer membrane that can bind well to the respiratory tract
Intestinal Tract: Bacteria can release enterotoxins that will damage the mucosa, they can survive in the ph and membrane. Viruses that are non enveloped are resistant to bile and the digestive enzymes present. Fungi: mainly in immunocompromised (not really seen in healthy people) (oral thrush)
Urogenital Tract: Antibiotics can kill normal flora and make the vagina susceptible to infection

Question 3

how are pathogens are disseminated into various organs and tissues.

Answer 3

The infection once it has got into either the lungs or an open wound if can go into the lymphatic system and to the bloodstream and distribute throughout the body

Question 4

What are the four major mechanisms by which microbes can evade immune defense?

Answer 4

Microbes can further invade by remaining inaccessible to the host immune system - C. Diff will produce a toxin that allows it to propagate in the lumen of the intestines. Our immune system in the intestines isn’t very strong so its easy for bacteria to invade
also by changing their outer proteins constantly so they are not as easily affected
They can resist phagocytosis and inactivate antibody functions

Question 5

Understand the mechanisms of viral entry

Answer 5

The virus in order to invade must be able to pass the membrane of the cell which is through a process known as entry and uncoating to get into the cytoplasm which allows it now to be replicated to make more genomes and messenger RNA to make protein. It can affect the cell’s DNA, RNA, and protein synthesis and can cause cell lysis or fusion, and metabolic derangement.
The whole goal of invasion is to create more copies that can spread and infect other cells in the body further invading the immune response
1. Host-cell receptors for a particular virus
- HIV: HIV has a gp120 protein that can bind to CD4 and CXCR4 which means any T cell that expresses CD4 and CXCR4 can be affected. also affected can be macrophages with CCR5 due to the binding of gp120 on HIV cells
- Rhinoviruses can bind to ICAM-1 which will repress the immune response
- COVID has spike protein ACE2 receptor
2. Cell type-specific transcription factors that recognize viral enhancer and promoter sequences
3. physical barriers

Question 6

Understand the mechanisms of bacterial injury.

Answer 6

they must adhere to cells, invade cells and tissue, and deliver toxins that will damage and allow the bacteria to invade further
Bacterial endotoxins - LPS a component of the gram-negative bacteria cell walls. It causes the production of effector cytokines. It helps the bacteria move through the body and invade further

Question 7

How can diphtheria toxin inhibit protein synthesis?

Answer 7

Has 2 subunits (cystine bond) that can exist in harsh environments and can bind to a host cell receptor and get engulfed once in the cell it breaks the sulfide bond
A subunit can catalyze an EF-2 reaction that is needed for protein synthesis and this change will inactivate and kill cells

Question 8

Understand the mechanisms of viral injury.

Answer 8

1. lysis of host cell
2. Immune cell-mediated killing
3. Alteration of the apoptosis pathway
   - homologues of the cellular BCL-2 that inhibit apoptosis allowing the cell to replicate and spread in the body
4. induction of cell proliferation and transformation resulting in cancer
5. can alter host cell DNA, RNA, or protein synthesis
6. Damage to the plasma membrane
7. Damage to cells involved in antimicrobial defense, leading to secondary infections