Innate immune system

Question 1

What is the innate immune system?

Answer 1

The first immune system to respond to a threat. It works by the production of cytokines to recruit the immune cells to the site of infection. The detection and removal is through specialised leukocytes and complement

Question 2

What are the primary protective barriers?

Answer 2

Anatomical barriers (skin and mucosal epithelium), chemical defences and commensal microflora

Question 3

How does the skin act as an anatomical barrier?

Answer 3

It has a low pH and through the secretion of antimicrobial peptides and proteins such as psoriasin against E.coli, and secretes fatty acids

Question 4

How does the mucosal epithelium act as an anatomical barrier?

Answer 4

The outer layers of the epithelium secrete mucus to prevent microbial adhesion, the mucus, as well as tears and saliva, contain lysozyme that will attack the cell wall of gram +ve bacteria. Epithelial cells in the lungs beat around to make it hard for microbes to latch onto

Question 5

What does lysozyme do to gram +ve bacteria?

Answer 5

It hydrolyses the peptidoglycan layer allowing lysis by defensins to happen on the cell membrane

Question 6

What are the pH levels on the skin vagina and in the stomach?

Answer 6

Skin - 5.5
Vagina - 4.5
Stomach - 2

Question 7

How does commensal microflora act as a protective barrier?

Answer 7

They compete with pathogens for attachment sites, nutrients, promote the maturation of immune cells, aid in polysaccharide digestion and absorption of nutrients by host gut cells, antimicrobial activity against pathogens

Question 8

What are the molecules of the innate immune system?

Answer 8

Soluble - antimicrobial peptides, cytokines, pattern recognition molecules and the complement
MHC I & II

Question 9

How does the innate immune system recognise pathogens?

Answer 9

It utilises fixed pattern recognition battery and is almost flawless in distinguishing between self and non-self. Microorganisms display particular pathogen-associated molecular patterns (PAMPS) not present in/on host cells, these PAMPS are detected by pattern recognition receptors (PRR). These PRR stimulate phagocytosis by direct recognition of PAMPS

Question 10

There are different type of PRR, name some and what they do

Answer 10

C-type lectin receptor - recognises particular carbs and binds to their residue
Opsonin recognition receptors - stimulate phagocytosis by binding to opsonins attached to the pathogen (complement receptors and Fc receptors that bind to opposite antibodies)

Question 11

What is an oxidative attack and a non-oxidative attack?

Answer 11

Non-oxidative attack - lysosomes merge with phagosome to form phagolysosomes and destroy protein
Oxidative attack - employs reactive oxygen and nitrogen species

Question 12

What are most complement molecules?

Answer 12

Proteases, secreted in inactive form

Question 13

How is the complement controlled and stopped?

Answer 13

Production of highly liable components, which undergo spontaneous inactivation if not stabilised and the production of inhibitory proteins

Question 14

What are the 4 systems activated during tissue damage?

Answer 14

Kinin, clotting, fibrinolytic and complement systems

Question 15

Why are neutrophils first to the site of infection?

Answer 15

Due to proteins expressed by cytokines to anchor them to the endothelial cells, 6 hours following the protein for monocytes, macrophages etc are synthesised

Question 16

What is TNF-alpha?

Answer 16

Activates macrophages and neutrophils, stimulates endothelial cells to initiate blood clotting in small vessels to contain pathogens, abundance of TNF-alpha synthesis can lead to septic shock

Question 17

What are the 2 layers of the skin?

Answer 17

Epidermis - consists of several tiers of tightly packed epithelial cells with the outer layer being mostly dead cells filled with a waterptoof protein called keratin
Dermis - composed of connective tissue and contains blood vessels, hair follicles, sebaceous glands sweat glands and scattered myeloid leukocytes such as dendritic cells, mast cells and macrophages

Question 18

How has the influenza virus evolved to evade the bodies defences?

Answer 18

Possesses a surface molecule that enables it to attach firmly to cells in mucous membranes of the respiratory tract, preventing it from being swept out by ciliated epithelial cells

Question 19

What do lactoferrin and calprotectin do?

Answer 19

Epithelial cells can secrete a broad spectrum of proteins and peptides that provide protections against pathogens, several are enzymes and binding proteins that kill or inhibit the growth of bacterial and fungal cells. Lactoferrin and calprotectin are proteins that bind and sequester metal ions needed by bacteria and fungi, limiting their growth

Question 20

Why is human skin resistant to the colonisation of E.coli?

Answer 20

A small protein of the S-100 family called Psoriasin that contains potent antibacterial activity against E.coli on the skin and tongue. But does not kill S.aureus, Calprotectin another member of the S-100 family does kill S.aureus but not E.coli

Question 21

How do antimicrobial peptides kill pathogens?

Answer 21

They are generally cysteine-rich, cationic and amphipathic (contain both hydrophilic and hydrophobic regions) because of their positive charge and they are amphipathic nature they interact with acidic phospholipids in lipid bilayers, disrupting the membranes of fungi, bacteria, viruses and parasites. They can then enter the microbe and carry out other toxic effects such as inhibiting the synthesis of DNA, RNA or proteins and activating antimicrobial enzymes resulting in cell death