L14 Innate Defence

Question 1

Types of PRR

Free receptors present in the serum

Answer 1

Mannose Binding Lectin

Ficolins

Question 2

Mannose Binding Lectin

Answer 2

• Binds to repetitive carbohydrate structure (mannan) found on 
a range of microbes 

• Not found in vertebrates 

• Activates lectin C’ pathway 

• Opsonize microorganisms

Question 3

Ficolins

Answer 3

• Contain carbohydrate recognition domains 

• After binding to carbohydrates on a microbe, they activate complement through the lectin pathway and thus contribute to clearance of the microbe 


Question 4

What are the membrane bound phagocytic receptors?

PRR

Answer 4

• Receptor mediated
− Complement receptor 

− Scavenger receptor : cellular break down products

− Mannose receptor

• Membrane enclosed endocytic vesicle phagosome 

• Fuses with lysosome phagolysosome

Question 5

Describe
membrane bound signaling receptors
PRR

Answer 5

Detect extracellular bacteria and microorganisms

• Toll-like receptors 
-> down stream effects
• Cell surface and membranes of intracellular vesicles 

• Recognize PAMPS
− Extracellular pathogens 

− Endocytosed extracellular components 


• Signaling induces the expression of inflammatory cytokines and chemokines 


Question 6

Describe Cytoplasmic signaling receptors

PRR

Answer 6

• Detect intracellular bacteria and virus 


NOD-like receptors- intracellular sensors of bacterial infection 


RIG-I like helicase – sensors of cytoplasmic RNAs 


Question 7

Cellular effectors of innate immunity

Answer 7

macrophages
neutrophils
NK
Dendritic cells

Question 8

Dendritic cells 
Interdigitating DC (or just DC)

Answer 8

DC-Located under epithelia and interstitia of all tissues
− Capture microbes

− Transport to lymphoid organs

− Present antigen for recognition by lymphocytes

Question 9

Dendritic cells

Follicular DC

Answer 9

FDC-Located in lymphoid follicles

− Trap antigen bound to antibody or complement
− Present antigen to B-cells

Question 10

What are dendritic cells?

Answer 10

Antigen presenting cells: 
(of the adaptive immune response?)
• Interdigitating DC (or just DC)
• Follicular DC

Question 11

NK cells

Answer 11

• Arise from common lymphoid progenitor 

• Innate immunity 

• Receptors recognize molecules expressed on
− IgG coated target cells (ADCC- antibody dependent cytotoxicity
− Infected cells

− Stressed cells 
includes cancer cells
− Cells with DNA damage 


Host cells that is infected/stressed/damaged DNA down regulates MHC 1 -> identification for NK cells
• Eliminate irreparably damaged cells and potential 
reservoirs of infection 

• Avoid attacking normal host cells through recognition of class I MHC molecules on healthy cells 

− Viral infections/ tumour cells up regulate MHC I

Question 12

Complement activation

Classical pathway

Answer 12

requires an adaptive immune response 

• Binding of IgM and IgG to pathogen induces conformational change in Fc region which initiates complement casacde
• Associated with adaptive immune response

Question 13

Complement activation

Lectin pathway

Answer 13

innate immune response 

• Activated when (PRR) bind to carbohydrate structures of certain pathogen
• Host derived soluble carbohydrate binding proteins (PRR) bind to carbohydrate structures of certain pathogen

Question 14

Complement activation

Alternative pathway

Answer 14

• Bacterial cell walls and endotoxins

Question 15

C3 effector process

complement activation

Answer 15

C3a being released, leading to chemical mediator recruitment and drawing to the site of injury

C3b being deposited on the microorganism->
Oposination- facilitate phagocytosis

Form MAC- pores in the membrane of the organism, cause direct death of microorganism

C3-opsoinsation
C5-inflammation
6,7,8-MAC