Week 2 (Part 1): Innate Immunity - First Line of Defence

Question 1

What is the main function of the immune system?

Answer 1

Main function is to protect body from pathogens that can make you sick

Question 2

What are the two immune systems?

- Describe what each is made up of

Answer 2

1) Innate immune system
- Barriers and innate cells

2) Adaptive immune system
- B Lymphocytes and T Lymphocytes

Question 3

What is the immune system continually challenged by? What are these called?

Answer 3

Challenged by a spectrum of chemical substances that it recognizes as foreign, or “nonself”
- These foreign substances are called antigens

Question 4

Give examples of infectious vs. non-infectious antigens:

Answer 4

Infectious

• Virus
• Bacteria
• Fungi

Non-infectious

• Bee venom
• Drug vaccines
• Transplant tissue

Question 5

What other types of abnormal cells can the immune system recognize and destroy?

Answer 5

Pre-cancerous cells

Question 6

What does INNATE mean?

Answer 6

In the body since birth

Question 7

What are properties of the innate immune system (5)?

Answer 7

1) Does not require memory and does not have memory (non-adaptive)
- Means this system can react on first exposure to the invading organism

2) Responds immediately
- But the fact that it does not have a memory of pathogens means it mounts the same immune response to an identical pathogen with each time it is exposed

3) Is always initiated when pathogen contacts body, but is non-specific
- The term non-specific means that it does not matter what the kind of pathogen it is, the innate system will respond, this is contrast to the adaptive immune system which responds to specific microbes and antigens

4) Uses Pattern Recognition
Receptors (PRRs) that recognize microbial structures
- These structures are shared by all microbes and are necessary for their survival but not present on human cells – thus the innate immune system is able to distinguish between self and nonself.

5) Has first and second lines of defense

Question 8

How do pathogens enter our body? (4)

Answer 8

1) Skin
- Breaks in the skin layers: trauma, burns, and wounds which makes them vulnerable to colonization and growth of bacteria

2) Respiratory tract
- Breath in airborne droplets from other peoples secretions (coughs, sneezes etc), touching a surface that has a pathogen on it and then touching our face, which allows the pathogen to invade into upper and lower respiratory tract
- We can also inadvertently swallow gastric sections into the respiratory system (called aspiration pneumonia)

3) GI tract
- Fecal oral contamination, bacteria in food

4) Urogenital tract
- This happens through local invasion or the skin or mucous membranes, usually through sexual contact, or by an ascending infection, whereby organisms can ascend through the urethra to infect the bladder and renal pelvis.

Question 9

What are physical barriers to pathogens?

Answer 9

Physical

1) Skin (tight junctions of epithelial cells)

2) Mucous Membranes (globlet cells produce
mucous, ciliated epithelial cells sweep it away)

Question 10

What provides the largest physical barrier to pathogens? How?

Answer 10

The skin provides the largest physical barrier to pathogens, mostly through epithelial cells that are tightly bound within the layers of the skin
- The skin has chemical barriers that create an acidic environment that discourages growth of many organisms, has Fatty acids , sweat and oil glands that kill many bacteria, and even the desquamation of old skin (which is a normal process helps remove offending organisms.

Question 11

How does the mucous membrane act as a barrier to pathogens?

Answer 11

The mucous membranes that line our eyes and mouth produce tears and saliva have an enzyme called lysozyme that kill bacteria

Question 12

Can the mucous membrane also have mechanical structures?

- Provide an example.

Answer 12

Yes

• There are mechanical structures within some mucous membranes that sweep pathogens away
• For example, epithelial cells in the respiratory tract have special ciliary projections that use a sweeping motion to remove foreign objects or pathogens. - Scattered throughout the cilia are goblet cells that secrete mucus which helps protect the lining of the bronchus and trap microorganisms

Question 13

What are chemical barriers to pathogens? Explain.

Answer 13

1) Stomach
- The stomach mainly uses an acidic environment to prevent which prevent bacterial colonization and growth, Antibacterial Peptides such as pepsin, and again an acidic pH that kills organisms.

2) The GI system
- The GI system also uses Microflora, or normal bacteria found in the gut, to helps to keep foreign bacteria in check

Question 14

What is one common misconception about micro-organisms and humans?

Answer 14

One common misconception should be dispelled from the start: not all interactions between microorganisms and humans are detrimental.

Question 15

What do microflora associate with? What do they compete with?

Answer 15

Microflora associate with epithelial cells that line all pathogen entry points
- They compete with pathogens for nutrients and attachment to epithelial cells

Question 16

What inhabits the internal and external surfaces of the human body

Answer 16

The internal and external exposed surfaces of the human body are normally, and harmlessly inhabited by a multitude of bacteria, collectively referred to as the normal microflora

Question 17

What do microflora produce? What type of interaction is this?

Answer 17

Microflora are present body’s normal population of bacteria, or flora, which produce chemicals that inhibit the growth of some invading bacteria – so it is a beneficial interaction for the most part, or what we sometimes call a symbiotic relationship.

Question 18

What does it mean that many normal flora are “opportunistic” pathogens?
- Provide an example.

Answer 18

They can become pathogenic when opportunity arises, such as when the health and immunity of the host have been severely weekend by illness, malnutrition or medical therapy
- A classic example of medical therapy allowing microflora to opportunistically cause infection in presented above in relation to C. Difficile.