27/03

Question 1

Where can we find and structure of TLR

Answer 1

TLR are homodimer or heterodimer receptor expressed on innate cells, T and B lymphocytes

Question 2

How can a TLR bind the molecule present on the pathogen?

Answer 2

1- MyD88 bind the IL1 receptor associated kinase (IRAK)
2- The phosphorylation of IRAK lead to the binding of TRAF6
3- MyD88-IRAK-TRAF6 bind the TIR domain on TLR
4- TLR dimerize

Question 3

How can a dendritic cell be activated?

Answer 3

1- A barrier has been broken and the bacteria enter the cell
2- The TLRs recognition induce the production of cytokines (TNF and interferon type 1)
3- A positive feedback mechanism activates macrophages
4- NK and T cells are recruited and activated
5- IL12 and IFN-γ are produced and act on dendritic cells
6- Dendritic cells start to phagocytise, change their shape increasing the expression of MHC (became mature dendritic cell) and move to the lymphoid organ and activate the active immunity by secreting factors that increases the expression of chemokine’s secretion

Question 4

What’s imiquimod?

Answer 4

A drug that contrast the misfunction of TLR, it’s used to stimulate an inflammatory response against HPV infection

Question 5

Which kind of cytosolic receptors exist?

Answer 5

• NLR (nod like receptors): recognize some peptidoglycans
• RLR (rig like receptors): recognize viral DNA
• CDS (cytosolic DNA sensor): recognize bacterial DNA

Question 6

What does the inflammasome do?

Answer 6

The inflammasome activates the caspase 1 that cleaves the pro-IL1 allowing the release of the active form.
IL1 may activate the NFkB pathway leading to an inflammatory response

Question 7

Which are the PRR that are usually present on immune cells’ surface? What do they do?

Answer 7

Scavenger receptor:
* Phagocytosis,
* Secretion of pro-inflammatory cytokines and reactive oxygen intermediates (ROI)
* Antigen presentation

C-type lectins:
* Phagocytosis
* Release of pro-inflammatory cytokines
* ROI productions
* Increase of cell adhesion and migration
* Activate complement

Toll like receptor:
* Anti-viral and anti-microbial activities
* Secretion of pro-inflammatory cytokines
* Production of ROI

NOD like receptors: Inflammasome assembly and release of IL1 and IL18

RIG like receptors: Production of interferons and other pro-inflammatory cytokines

Cytosolic DNA sensor:
* Release of interferons and other cytokines
* Destruction of viral DNA
* Inhibition of protein synthesis

Question 8

Which are the main features of cytokines?

Answer 8

• Small dimension (17-20kDa)
• They work in dimers
• Short half-life
• Redundant: there are more cytokine for the same job
• Pleiotropic: they can affect different cells and have different effect on the same cell
• Synergic: they can initiate the same function together or antagonize with other cytokines
• Polarized: cytokines are secreted just in specific point (polarized manner) in order to avoid the dispersion of the cytokines produced

Question 9

With which general mechanism can a cytokine work?

Answer 9

Autocrine: on the same cell that release it
Paracrine: on close cells with the right receptor
Endocrine: blood circulation

Question 10

Which kind of cytokine receptor can we have and which structure do they have?

Answer 10

IFN: heterodimers
common gamma chain: heterodimers/trimers
common beta chain: heterotrimers
IL1: homodimers
IL2: heterodimers/trimers
TNF: homotrimers

Question 11

IL2 receptor: structure

Answer 11

2 or 3 chains (alfa, beta and gamma), beta and gamma transduce the signal.
A cell can be pre-activated in order to have the chain already expressed on the membrane before the arrive of the signal.

Question 12

Effect of IL2

Answer 12

activation and proliferation of T, B and NK cells

Question 13

Which are the main function of chemokines

Answer 13

Constitutive chemokines: physiological extravasation of immune cells: CXCL12 (B cells), CCL19 and CCL21 (T cells)
Inflammatory cytokines: CCL2

Question 14

Which chemokines receptor has an impact on HIV

Answer 14

CCR5: it’s receptor is used by HIV viruses to enter the cells and infect them

Question 15

Which structure can activate the classical pathway of the complement?

Answer 15

The binding between 2 glomerular head of C1q and two antibodies with the consequent autocleavage

Question 16

How can we activate the lectinic pathway?

Answer 16

Mannose binding protein (MBP) and ficolins must recognize foreign sugars on microbe surfaces

Question 17

How can the complement actually defend the organism from the bacteria?

Answer 17

Each pathway terminate with the assembly of the MAC (Membrane attack complex) which can open a pore in the membrane of the pathogen

Question 18

How does the alternative pathway start?

Answer 18

The factor B stabilize C3b, then the complex is cleaved by factor D into Ba and Bb. Bb can bind C3b acquiring a convertase activity stabilized then by properdin.
It’s a spontaneus C3 cleavage

Question 19

Which biological functions are mediated by the complement?

Answer 19

Cell killing
Opsonization
Induction or amplification of local inflammatory response
Immunocomplex removal

Question 20

What’s the opsonization?

Answer 20

The components of the complement (especially C3b) cover the antibodies on the cell surface of many bacteria, virion and infected cells. In this way the cell can be phagocytize by macrophage.

Question 21

How can the complement modulate a inflammatory response?

Answer 21

all the soluble complement fragment that get released after the cleavage cause:
- a local inflammatory reaction
- an increase of size and permeability of local blood vessels
- cause the oxidative burst

Question 22

How can the complement mediate the immunocomplex removal?

Answer 22

C3b bind the antibody and it’s recognized by C1 receptor on erythrocytes, then they’re carried towards the spleen or the liver

Question 23

How can we inhibit the classical pathway?

Answer 23

Using C1inh, a soluble molecule that binds C1r and C1s mimiking C4

Question 24

Which are the characteristics of the genes of both MHC class 1 and 2?

Answer 24

o Polygenic: there are multiple genes involved in the phenotype (multiple loci)
o Polymorphic: for each gene there are different isoforms in a population due to single nucleotide polymorphisms (SNPs) or polymorphism of hundreds of base pairs
o Co-dominant

Question 25

Structure of MHC class I

Answer 25

They have an α chain (polymorphic) with 3 globular domains (α1, α2, α3) and they’re associated with a β2 microglobulin chain with a glomerular domain.

Question 26

How can MHC class I present the peptide

Answer 26

α1 and α2 generate what we call pocket in which there has to be a peptide. The peptide has to be 8-10 amino acids long and with anchor residues necessary for the correct binding to MHC class I.

Question 27

Structure of MHC class II

Answer 27

It’s a heterodimer with an α and a β chain, each with 2 globular domains (α1, α2, β1, β2). There’s a pocket between the α1 and the β1 domain which can contain a peptide of 13-20 amino acids. The presence of anchor amino acids is not needed.

Question 28

In which cells can we find MHC class II?

Answer 28

dendritic cells, Langerhans cells, B cells and thymic epithelial cells.
With class II trans activators (CIITA) it can be induced also in other cells

Question 29

Which kind of peptides show the MHC class I and II?

Answer 29

class I: peptides created by the LMP2-LMP7 modified proteasome (endogenous)
class II: residues of phagocytized and lysed pathogens (exogenous)

Question 30

Describe the process that lead to the presentation of the peptide by the MHC class I

Answer 30

1- Infection -> production of cytokines such as INFγ
2- The immunoproteasome (LMP2 and LMP7) cut the proteins (not necessary ubiquitinated)
3- Formation of peptides
4- Entrance of peptides in the ER thanks to TAP1 and TAP2 while the MHC chains are hold in place by calnexin and careticulin
5- Presentation on the surface of the cell on the groove of the MHC thanks to the tapasin

Question 31

What’s the role of the invariant chain in the MHC?

Answer 31

It maintain the structure of the pocket of MHC class II complex

Question 32

What is the cross presentation of an antigen?

Answer 32

is performed by dendritic cells and allow the presentation of exogenous proteins and peptides coming from phagocytized pathogen in MHC class I molecules.
Dendritic cells are able to express Sec61 which is a protein that form a pore channel in the phagosomes and allows some of the peptides present inside the phagolysosome to reach the cytosol

Question 33

How can a cell present non-proteic antigens?

Answer 33

other antigens like lipidic antigens can be presented by non-classical HLA molecules. They’re then recognized by gamma-delta T cells and invariant NK cells