Antiviral Immunity Flashcards
What is the main function of dendritic cells?
A) To produce antibodies
B) To present antigens to T-cells
C) To directly kill pathogens
D) To produce cytokines only
E) To activate B-cells only
B) To present antigens to T-cells
What are naïve T-cells?
T-cells that haven’t seen antigen yet
What cells can activate naïve T-cells both in vivo and in vitro?
Dendritic cells. No other cells can do this.
Which of the following is TRUE about immature dendritic cells?
A) They are efficient at antigen presentation
B) They have high expression of co-stimulatory molecules
C) They are inefficient at antigen capture
D) They are efficient at antigen capture but inefficient at antigen presentation
E) They express high levels of MHC class II on their surface
D) They are efficient at antigen capture but inefficient at antigen presentation
Which endocytic pathway in dendritic cells involves the formation of large vesicles (1-5μm) from the plasma membrane?
A) Receptor-mediated endocytosis
B) Phagocytosis
C) Macropinocytosis
D) Exocytosis
E) Caveolae-mediated endocytosis
C) Macropinocytosis
Which receptor type do dendritic cells use to recognize glycosylated proteins?
A) Toll-like receptors
B) Fc receptors
C) C-type lectins
D) Scavenger receptors
E) Heat shock protein receptors
C) C-type lectins
Which of the following is NOT a direct danger signal recognized by toll-like receptors (TLRs)?
A) Lipopolysaccharide (LPS)
B) Tumor necrosis factor-α
C) Double-stranded RNA
D) Bacterial lipoproteins
E) Flagellin
B) Tumor necrosis factor-α
What happens to E-cadherin expression during dendritic cell maturation?
A) It increases
B) It remains unchanged
C) It is reduced
D) It is completely eliminated
E) It is relocated to the nucleus
C) It is reduced
Which chemokine receptor is upregulated during dendritic cell maturation to enable homing to lymph nodes?
A) CXCR4
B) CCR5
C) CCR7
D) CXCR3
E) CCR2
C) CCR7
What is the effect of maturation on protease activity in dendritic cells?
A) Protease activity is reduced
B) Protease activity increases
C) Protease activity remains unchanged
D) All proteases are eliminated
E) Proteases are relocated to the nucleus
B) Protease activity increases
What is “cross presentation” in dendritic cells?
A) Presentation of self-antigens on MHC class II
B) Presentation of exogenous antigens on MHC class I
C) Presentation of endogenous antigens on MHC class II
D) Direct presentation of unprocessed antigens
E) Exchange of antigens between dendritic cells
B) Presentation of exogenous antigens on MHC class I
Which co-stimulatory molecules are upregulated during dendritic cell maturation?
A) CD3 and CD4
B) TCR and CD28
C) B7.1 and B7.2
D) MHC I and MHC II
E) CD36 and DEC205
C) B7.1 and B7.2
Which of the following molecules inhibits the cleavage of invariant chain by cathepsin S in immature dendritic cells?
A) Tapasin
B) Calnexin
C) Cystatin C
D) ERP57
E) β2-microglobulin
C) Cystatin C
What happens to the endosomal/lysosomal pH during dendritic cell maturation?
A) It increases (becomes more basic)
B) It decreases (becomes more acidic)
C) It remains unchanged
D) It fluctuates rapidly
E) It becomes neutral
B) It decreases (becomes more acidic)
Why is cross presentation important for initiating adaptive immunity?
A) It allows presentation of bacterial antigens only
B) It prevents autoimmunity
C) It allows dendritic cells to present antigens from pathogens that don’t directly infect them
D) It increases antibody production
E) It activates natural killer cells
C) It allows dendritic cells to present antigens from pathogens that don’t directly infect them
Where are the ligands for CCR7 expressed?
A) In bone marrow only
B) In all peripheral tissues
C) In lymphatic vessels and T cell zones of lymph nodes
D) Only in inflamed tissues
E) Only in the thymus
C) In lymphatic vessels and T cell zones of lymph nodes
Concerning immature dendritic cells:
A. They are efficient at antigen presentation;
B. They express high levels of co-stimulatory molecules;
C. They have a high endosomal/lysosomal pH;
D. They sample antigens using macropinocytosis;
E. They primarily reside in lymph nodes.
C, D
The following receptors are involved in antigen capture by dendritic cells:
A. CD3;
B. CCR7;
C. Mannose receptor;
D. CD4;
E. MHC class I.
C
Concerning toll-like receptors (TLRs) on dendritic cells:
A. TLR2 recognizes lipopolysaccharide from Gram-negative bacteria;
B. TLR4 recognizes Gram-positive bacterial cell wall compounds;
C. TLR3 recognizes double-stranded RNA;
D. TLRs inhibit dendritic cell maturation;
E. TLRs have no effect on macropinocytosis.
c
The following molecules are important for dendritic cell migration to lymph nodes:
A. E-cadherin;
B. CCR7;
C. DEC205;
D. B7.1;
E. Invariant chain.
B - CCR7
Regarding MHC class II in dendritic cells:
A. It is highly expressed on immature dendritic cells;
B. It is assembled in the MHC class II compartment (MIIC);
C. It primarily presents endogenous antigens;
D. Its expression decreases upon maturation;
E. It interacts with CD8 on T-cells.
B
Concerning cross-presentation by dendritic cells:
A. It involves presenting endogenous antigens on MHC class II;
B. It is important for activating CD4⁺ T-cells;
C. It presents exogenous antigens on MHC class I;
D. It requires proteasome-independent processing;
E. It only occurs in plasmacytoid dendritic cells.
C. It presents exogenous antigens on MHC class I
The following statements about dendritic cell maturation are correct:
A. It decreases expression of MHC class I;
B. It increases expression of B7.1 and B7.2;
C. It enhances E-cadherin expression;
D. It decreases antigen processing;
E. It reduces migration to lymph nodes.
B. It increases expression of B7.1 and B7.2;
Concerning the regulation of MHC class II in dendritic cells:
A. Cystatin C promotes invariant chain cleavage;
B. Mature dendritic cells have increased cystatin C levels;
C. Immature dendritic cells have high protease activity;
D. Mature dendritic cells have reduced endosomal pH;
E. Maturation inhibits MHC class II synthesis.
D. Mature dendritic cells have reduced endosomal pH
The following molecules are chemokine ligands for CCR7:
A. TNF-α;
B. CCL19;
C. B7.1;
D. Prostaglandin E2;
E. LPS.
B. CCL19;
Dendritic cells are capable of:
A. Antibody production;
B. Activating naïve T-cells;
C. Developing from plasma cells;
D. Releasing histamine;
E. Expressing TCR complexes.
B. Activating naïve T-cells;
The following statements about macropinocytosis in dendritic cells are correct:
A. It forms small vesicles around 0.1 μm in diameter;
B. It is receptor-dependent;
C. It increases permanently after TLR activation;
D. It is constitutive in immature dendritic cells;
E. It specifically targets opsonized particles.
D. It is constitutive in immature dendritic cells;
The following statements about phagocytosis by dendritic cells are correct:
A. It is a mechanism for non-specific uptake of fluid;
B. It is mediated by plasma membrane ruffling;
C. It can uptake bacterial and fungal pathogens;
D. It only occurs after maturation;
E. It is less efficient than in macrophages.
C. It can uptake bacterial and fungal pathogens;
Regarding co-stimulation by dendritic cells:
A. It is mediated by MHC molecules;
B. It involves interaction between CD28 and B7 molecules;
C. It is highest in immature dendritic cells;
D. It is required to inhibit T-cell activation;
E. It is mediated by CCR7.
B. It involves interaction between CD28 and B7 molecules;
Concerning the MHC class I pathway in dendritic cells:
A. It exclusively presents exogenous antigens;
B. It requires the transporter associated with antigen processing (TAP);
C. It is not expressed in mature dendritic cells;
D. It interacts primarily with CD4 on T-cells;
E. It involves the invariant chain.
B. It requires the transporter associated with antigen processing (TAP)
The following molecules are indirect signals that trigger dendritic cell maturation:
A. Double-stranded RNA;
B. Flagellin;
C. Tumor necrosis factor-α;
D. LPS;
E. Bacterial lipoproteins.
C. Tumor necrosis factor-α
What are the 3 methods of capturing and uptake of antigens that DCs emplore?
Macropinocytosis, receptor-mediated endocytosis, phagocytosis
Describe macropinocytosis.
- Formation of large vesicles from the plasma membrane (1-5 micrometres diameter)
- Requires formation ruffles on the surface of the DC - the ruffle extends and captures the antigen to fuse with plasma membrane, forming a macropinosome that moves into the cell
- Constitutive in immature DCs (continuously sampling environment)
- Enables non-specific uptake of large amounts of surrounding fluid and antigens in the fluid phage
What are the capturing receptors that DCs express?
C-type lectins
Fc receptors
Scavenger receptors
Heat shock protein receptors
What do C-type lectins interact with?
Sugar molecules (glycosylated proteins)
What are the examples of C-type lectin receptor?
mannose and DEC205
What do Fc receptors recognise?
They recognise antibody complexes.
Fc-gamma-RI and Fc-epsilon-RI bind to the Fc (constant) portion of antibodies and internalise immune complexes
FcγRI (CD64) – High-Affinity Receptor for IgG
FcεRI – High-Affinity Receptor for IgE
What is an example of a scavenger receptor and what does it bind?
CD36 apoptotic bodies
What do HSP receptors bind?
Bind Hsc70 and gp96 (both heat-shock proteins) from tumour cells/infected cells and mediate uptake of HSP-peptide complexes
What is phagocytosis?
Receptor-mediated uptake of large particulate species.
What do DCs phagocytose?
Almost any bacterium
Yeast cells and fugal hyphae
Apoptopic and necrotic bodies
What do TLRs do?
They recognise direct danger signals
What direct signals do … recognise:
1) TLR2
2) TLR3
3) TLR4
4) TLR5
1) Gram+ bacterial cell wall compounds, bacterial lipoproteins
2) Double stranded RNA
3) LPS gram- bacteria
4) Flagellin from gram + and - bacteria
What are the indirect signals that can trigger DC maturation?
Tumour necrosis factor - a
interleukin-1-beta
prostaglandin E2
Describe the two functional states of DCs.
Dendritic cells exist in two functional states:
Immature DCs → Specialize in antigen capture (high macropinocytosis and phagocytosis).
Mature DCs → Specialize in antigen presentation (high MHC expression, low antigen uptake).
Before TLR activation: DCs are in the “capturing but not presenting” mode.
After TLR activation and maturation: DCs shift to “presenting but not capturing” mode.
Describe the process of when a danger signal activates TLRs.
Danger signals (like PAMPs from pathogens) activate TLRs, triggering:
A short burst (pulse) of antigen uptake via macropinocytosis.
DC maturation, which suppresses further antigen uptake.
Upregulation of MHC and costimulatory molecules, switching the DC into antigen-presentation mode.
What does “antigen-presentation mode” of a DC mean?
Mature DCs express high levels of MHC I and MHC II to efficiently present processed antigens to CD8+ and CD4+ T cells.
This mode ensures that DCs stop taking up new antigens and focus on activating the adaptive immune response.
Which MHC class is associated with CD8 cells?
MHC class I
What are some differences between the MHC class I and II pathway?
MHC-I deals with intracellular threats (e.g., viruses, tumors) and triggers cytotoxic T cell responses.
MHC-II handles extracellular threats (e.g., bacteria, fungi) and initiates helper T cell responses to coordinate immunity.
MHC II - Presents extracellular antigens to CD4+ cells
MHC I - presents intracellular antigens to CD8+ cytotoxic T-cells
MHC I - Proteasome degrades cytosolic proteins into peptides and proteins transported by Peptides transported to ER by TAP (Transporter associated with Antigen Processing)
MHC II - Lysosomal proteases degrade antigens in endosomes and Peptides loaded onto MHC-II in endosomal compartments
MHC I expressed on all nucleated cells for broad immune surveillance, MHCII only on professional APCs (DCs, macrophages, B-cells)
What is cross-presentation by DCs?
When DCs present extracellular antigens on MHC Class I molecules to T cells (breaking the rules) - only unique to DCs
Why is cross-presentation important?
It is important for the initiation of adaptive immunity. Not all infectious agents infect dendritic cells, but DCs are required to activate naïve CD8+ T-cells
Why is co-stimulation important?
The absence of co-stimulation will not lead to T-cell activation. T-cells require two signals from APCS.
Signal 1 is antigen-specific
Signal 2 provides the co-stimulation from APCs
- co-stimulatory molecules are CD80 and CD86, they bind to CD38 on the T cell, providing the second signal
