Initiation of Acquired Immune Response - T cells

Question 1

What type of antigens to T cells recognise?

Answer 1

Peptide antigens

Question 2

What do T cells express?

Answer 2

Single antigen receptor - T cell receptor (TCR)

Question 3

How do T cells have specificity?

Answer 3

There is a hypervariable tip of the TCR which is involved in binding to a specific antigen

Question 4

How do T cells recognise peptide antigens?

Answer 4

The antigen needs to be processed and presented to the TCR with Major Histocompatibility Complex (MHC) molecules

Question 5

What is another name for MHC?

Answer 5

Human Leucocyte Antigens (HLA)

Question 6

What is the role of MHC?

Answer 6

To display peptide antigens to T cells

Question 7

What are the features of Class I MHC?

Answer 7

Expressed on all nucleated cells and present antigens to CD8+ T cells

Question 8

What are the features of Class II MHC?

Answer 8

Only expressed on professional Antigen Presenting Cells (APC) - dendritic cells, macrophages and B cells. Present peptide antigen to CD4+ T cells

Question 9

What is the role of dendritic cells?

Answer 9

The bridge between the innate and acquired immune system - main function is to process and present antigens on the cell surface to T cells (APCs). Also phagocytic cells

Question 10

How do dendritic cells fight infection and inflammation?

Answer 10

1. Particles and antigens derived from pathogens are released by phagocytes
2. Dendritic cells phagocytose pathogen-derived particles and antigens
3. Pro-inflammatory TNFa stimulates immature tissue-resident DC to increase expression of co-stimulatory molecules
4. DCs digest ingested proteins and display small peptides derived from these on their cell surface = complex for MHC

Question 11

What is a naive T cell?

Answer 11

A T cell that has never seen an antigen

Question 12

What is the intermediate between naive T cells and effector T helper cells?

Answer 12

T helper 0

Question 13

What are 4 main type of effector T cells?

Answer 13

Th1, Th2, Tfh and regulatory T cells (fh=follicular helper)

Question 14

What do antigen-activated CD4+ T cells secrete?

Answer 14

A T cell growth factor, Interleukin 2 (IL-2) for autocrine-mediated cell proliferation

Question 15

What is the role of Th0?

Answer 15

Induce autocrina-/paracrine mediated proliferation of CD4+ and CD8+ cells as they produce lots of IL-2

Question 16

What is IL-2 used by?

Answer 16

Antigen activated CD4+ T cells and CD8+ T cells to allow them to proliferate and differentiate

Question 17

What happens when Th1 cells migrate out of the lymph nodes and enter sites of inflammation/infection?

Answer 17

Re-activated by the infected, tissue-resident macrophages (antigen specific) - infected macrophages express bacterial peptide antigens on their cell surface (with MHC II). The Th1 cells secrete pro-inflammatory cytokines, which enhances macrophage-mediated killing of internal pathogens = production of reactive oxygen species

Question 18

How can some pathogens evade phagolysomal killing by macrophages?

Answer 18

Infect and propagate in macrophages by escaping the phagosome.

Question 19

How do macrophages prevent pathogenic evasion?

Answer 19

Macrophages that respond to Th1 signals become super killers (like neutrophils)

Question 20

Where are effector Tfh cells re-stimulated by B cells?

Answer 20

In the B cell zone of the lymph node (antigen specific)

Question 21

What does the re-stimulated effector Tfh cell do?

Answer 21

Stimulate B cells to clonal proliferate and differentiate into a) long-lived plasma cells which secrete high affinity antigen-specific antibodies - IgM to IgG (in Germinal Centre reaction) OR b) long-lived memory B cells (Bm cells)

Question 22

How are cytotoxic T lymphocytes (CTLs) produced?

Answer 22

Antigen-activated CD8+ cells proliferate and differentiate

Question 23

What do CTLs do?

Answer 23

Migrate out of the lymph node and enter sites of infection to kill virally infected host cells

Question 24

How do CD8+ proliferate and differentiate into CTLs?

Answer 24

CD4+ cells differentiate in different Th cells that provide IL-2 to promote the proliferation and differentiation

Question 25

How do CTLs kill infected host cells?

Answer 25

1. CTL recognises and binds to virally infected cell
2. CTL programs target death inducing DNA fragmentation
3. CTL migrates to new target
4. Target cell dies by apoptosis

Question 26

How do CTLs recognise virally infected cells?

Answer 26

As all nucleated cells express MHC-I on their surface when the cell becomes infected, it presents viral-peptides