Cell-Mediated Immunity

Question 1

What are the two T-cell co-receptors and what type of effector cells do they give rise to?

Answer 1

1) CD4 - T-helper (TH1, TH2, TH17, TFH), T-regulatory
2) CD8 - Cytotoxic T-cells

Question 2

T-cells recognize antigens only when ____

Answer 2

Presented by APCs on either MHC I or MHC II - creating a unique peptide-MHC complex recognized by that particular TCR

Question 3

MHC is also known as ____.

Answer 3

HLA

Question 4

All nucleated cells display MHC ____.

Answer 4

Class I

Question 5

Professional APCs display MHC ____.

Answer 5

Class I and II

Question 6

Differentiation of CD4+ T-cells into respective effector cells is driven by…

Answer 6

Cytokines

Question 7

How are TH1 cells activated and what is their function?

Answer 7

Activated via IFN-γ and via CD40L binding CD40, they help activate macrophages to phagocytose

Question 8

What is the function of TH2 cells?

Answer 8

• Important in allergic pathways
• They release cytokines to promote class switching of B cells to secrete IgE, and recruit mast cells and eosinophils

Question 9

What is the function of TH17 cells?

Answer 9

• Release cytokines that promote neutrophils and other phagocyte recruitment
• Helpful for fungal infections

Question 10

What is the function of TFH cells?

Answer 10

Bind to B cells to activate them, initiating humoral immunity (isotype switching, Ab production)

Question 11

What is the function of Treg cells?

Answer 11

Help to suppress and regulate the immune response

Question 12

How does immunotherapy work?

Answer 12

Causes a shift from TH2 pathway to TH1, helping to increase tolerance to allergens

Question 13

Intravesicular pathogens may persist within phagolysosomes; these are killed via the ____ effector pathway.

Answer 13

TH1

Question 14

How are peptides loaded onto MHC I?

Answer 14

• After MHC I is assembled in the ER, viral proteins in the cytosol are cleaved by proteosomes and transferred to the ER, where they are loaded onto MHC I
• Peptide-loaded MHC I then “buds” off ER and goes to cell surface where it will alert CD8+ T cells

Question 15

Like B-cells, variable regions of the TCR are made via…

Answer 15

Somatic recombination (aka VDJ recombination)

Question 16

What are TRECs?

Answer 16

• T-cell receptor excision circles are the segments of DNA that are excised during VDJ recombination.
• TRECS remain but do not replicate and are diluted over time
• Measured in newborn screening; no TRECS = no T cells

Question 17

What is positive selection?

Answer 17

TCR must bind to self-MHC with some loose affinity to be selected; double positive thymocytes will then commit to either CD4 or CD8

Question 18

Where does self-MHC come from for T cell development in the thymus?

Answer 18

Thymic cortical epithelial cells

Question 19

What is negative selection?

Answer 19

If double-positive thymocytes bind too strongly to self-MHC, self-peptide complexes, they will undergo apoptosis (to avoid autoimmunity)

Question 20

What are the three requirements for T cell activation?

Answer 20

1) TCR has to bind to MHC-peptide complex
2) Co-stimulatory molecules between APC and T cell must bind
3) Cytokines from the APC must activate the T cell

Question 21

T cells both produce and require which cytokine for proliferation/division?

Answer 21

IL-2

Question 22

What are two mechanisms by which CTLs induce apoptosis?

Answer 22

1) FAS pathway - binding of CTL Fas ligand to Fas on target cell
2) Formation of pores via perforin and release of granzymes into pores

Question 23

The most common cause of CD4+ T cell deficiency is…

Answer 23

HIV