T Cells, Effector Functions and the MHC

Question 1

Definition of major histocompatibility complex

Answer 1

Set of genes that code for cell surface proteins essential for acquired immune system to recognize foreign molecules

Question 2

Definition of polygenic

Answer 2

A trait that is controlled by many genes

Question 3

Definition of polymorphic

Answer 3

Occurrence of 2 or more genetically determined phenotypes in a certain population

Question 4

Describe MHC I

• function
• structure
• how many AA displayed

Answer 4

Function
-express proteins synthesized in cells

Structure

• 1 transmembrane AP site
• a1-3, b2 attached ionically
• DSB within each chain

How many AA displayed
-8-15AA

Question 5

Describe MHC II

• function
• structure
• cells
• how many AA displayed

Answer 5

Function
-express proteins from exogenous sources

Structure

• 2 transmembrane AP site
• a1-2, b1-2
• DSB within each chain

Cells

• dendritic cells
• B cells
• macrophages, tale up antigens via exocytosis

How many AA displayed
-8-15AA

Question 6

Describe the polygenicity of MHC I

Answer 6

HLA on chromosome 6

Class 1

• A
• B
• C

3 distinct genes => 3 different proteins

Question 7

Describe the polygenicity of MHC II

Answer 7

HLA on chromosome 6

Class 2

• DP
• DQ
• DR

3 distinct gene pairs => 3 different proteins

Question 8

Describe the polymorphicity of MHCs

Why is this important

Answer 8

Codominant HLA regions inherited
Many alleles associated with HLA regions
Gene spliced => combination results in an MHC that can present a specific sequence of AA

Impossible for antigen to evoke detection by forming an antigen that cannot bind to any HLAs

Question 9

Describe the T cell receptor and types

• structure
• diversity
• CD8
• CD4

Answer 9

Structure
-heterodimer ab/ys joined by DSB

Diversity

• VCJ/VDJC, gene rearrangement, junctional diversity
• no affinity maturation

CD8
-CD8 and TCR

CD4
-CD4 and TCR

Question 10

How to activate T cells

Answer 10

Signal 1
-TCR, MHC interaction, strong enough to cause sustained signalling => specificity

Signal 2

• APC CD86, TC CD28 costimulation
• Costimulatory molecules unregulated on APC by danger signals

Question 11

What happens when CD8 is activated

Answer 11

MHC I with viral/cancer related proteins binds to specific TCR

Kills cell via perforin, granzymes

Question 12

What happens when CD4 is activated

Answer 12

MHC II on APCs

-effector Th1, 2, 17, Treg

Question 13

What is Th1

• activated by
• secretes
• function
• pathogen examples

Answer 13

Activated by
-IL12

Secretes

• IFN y => macrophage activation
• IL2 => CD8 activation

Function
-intracellular pathogens

Pathogens

• Listeria
• TB
• Leprosy

Question 14

What is Th2

• activated by
• secretes
• function
• pathogen examples

Answer 14

Activated by
-IL4

Secretes
-IL4, 13 => B cell affinity maturation, activation, class switching

Function
-Extracellular parasites

Pathogens

• Schistosomes
• Triconella

Question 15

What is Th17

• activated by
• secretes
• function
• pathogen examples

Answer 15

Activated by

• IL6
• TGFb

Secretes

• IL17, 21, 22 => antimicrobial secretions from epithelium
• Aid wound healing, neutrophil maturation

Function
-Extracellular pathogens

Pathogens
-Krebsiella, fungi

Question 16

What is Treg

• activated by
• secreted
• function
• pathogen examples

Answer 16

Activated by

• IL2
• TGFb

Secretes

• TGFb
• IL10

Function
-Suppress APC, effector cell function