30.3 - Defence Against Infectious Disease_Innate Mechanisms

Question 1

What is the difference between the innate and the specific immune response?

Answer 1

The immune system is divided into nonspecific (innate) and specific (adaptive) responses. Nonspecific defences, like skin and stomach acid, block pathogens indiscriminately. Specific defences, such as B and T lymphocytes, adapt to specific pathogens after exposure.

Question 2

Give examples of how the innate and specific immune responses interact.

Answer 2

*Dendritic cells activate T-cells -> major mode of communication between the 2 responses.
*Abs bind to phagocytes Fc region to increase efficiency of recognition.
*CKs secreted by T cells improve effectiveness of innate immunity.

Question 3

List the cells of the innate immune system

Answer 3

Leukocytes:
-Neutrophils
-Eosinophils
-Basophils
-Monocytes
-Mast cells
-Macrophages (tissues)
-Dendritic cells

Question 4

What are the barriers to infection?

Answer 4

Skin, mucus, gastric acid, bile salts, normal microbiota.

Question 5

How do innate immune cells detect pathogens?

Answer 5

Innate immune cells have pattern recognition receptors (PRRs) that recognise a molecular pattern called a pathogen associated molecular pattern (PAMP) on the surface of microbes

Question 6

Name the four PRRs

Answer 6

Toll like receptors (TLRs)
C type lectin receptors
NOD-like receptors (NLRs)
RIG-I Helicase receptors (nucelic acid receptors)

Question 7

What are inflammasomes?

Answer 7

They are innate immune system receptors/sensors that regulate the activation of caspase-1 + induce inflammation in response to infectious microbes and molecules derived from host proteins.

Question 8

What are the different effector functions in the innate immune response??

Answer 8

• Respiratory burst
• Degranulation
• Phagocytosis + phagolysosomal degradation.

Question 9

What is respiratory burst?

Answer 9

the rapid release of the reactive oxygen species (ROS), superoxide anion (O 2) and hydrogen peroxide (H 2O 2), from different cell types.

Question 10

Which cells perform respiratory burst?

Answer 10

Neutrophils, monocytes, and macrophages.

Question 11

Which cells degranulate?

Answer 11

Mast cells, eosinophils, basophils.

Question 12

Which cells are capable of phagocytosis and phagolysosomal degradation?

Answer 12

Neutrophils and macrophages.

Question 13

How does opsonisation aid phagocytosis?

Answer 13

Opsonins, such as antibodies (IgG, IgA) and complement proteins (C3b, C4b), bind to the surface of pathogens. This binding facilitates the attachment of pathogens to phagocytes (macrophages and neutrophils) through Fc receptors on the phagocytes.

Question 14

What are natural killer cells?

Answer 14

Cytotoxic lymphoycte which kill virus infected cells and tumour cells
They produce IFN- gamma which activates macrophages to kill ingested bacteria

Question 15

What soluble molecules are involved in the innate immune response?

Answer 15

Complement, (Classical, alternative and MBP pathways), type 1 interferons (alpha and beta), type 2 interferon (gamma) and other secreted molecules.

Question 16

Give an example of an innate immune evasion strategy.

Answer 16

Avoidance of phagocytosis by capsules (e.g. Streptococcus)
*leukocyte attachments and ROS-induced breakdown become more challenging

Question 17

What are the chemical barriers to infection? How do they work?

Answer 17

*Gastric acid (HCl) - denatures proteins and kills pathogens
*Bile salts - inhibit binary fission and regulate gut inflammatory pathways
*Surfactant - binds to surface of microbes to facilitate phagocytosis
*Antimicrobial peptides - (Defensin) made throughout skin and mucous *Membranes - highly positively charged that create pores in lipid membranes of pathogens

Question 18

What are the mechanical barriers to infection?

Answer 18

*Skins epidermis - keratinised squamous epithelial cells
*Mucous membranes - Coated in mucins (sticky mixture making penetration of respiratory, GI and genitourinary infections more difficult)

Question 19

What is the mechanism of action of type I interferons?

Answer 19

ANTIVIRAL = BLOCK SYNTHESIS OF VIRAL PROTEINS
They have NO effect on extracellular virus particles
Bind to cell surface
Signals to the cell to synthesise three antivral proteins

Question 20

What is the mechanism of action of type II interferons?

Answer 20

Active against intestinal viruses (rotavirus and norovirus)