Immunology: Principles

Question 1

What are the two types of lumped tissue and what do they do?

Answer 1

Primary (central) - where lymphocytes are generated/matured

Secondary - Where lymphocytes interact with antigen presenting cells (APC’s) and immune responses are generated

Question 2

Where can you find primary lymphoid tissue?

Answer 2

Bone marrow, thymus, bursa of fabricius
Illegal payers patches (in cattle, horses, dogs)
Appendix/caecal patch in rabbits

Question 3

Where can you find secondary lymphoid tissue?

Answer 3

– Lymph nodes
– Mucosal-associated lymphoid tissue (MALT, e.g. BALT)
– Spleen

Question 4

What do naive lymphocytes do until they are activated?

Answer 4

Naïve lymphocytes recirculate through blood and lymph continuously until they encounter their specific Ag in the LN

Question 5

When lymphocytes encounter their antigen what happens?

Answer 5

This stimulates cell activation, division, lymph node enlarges, activated Lymphocytes leave LN in lymph, enter blood via thoracic duct then enter tissues at site of infection.
Part of this response is to form memory cells

Question 6

What do memory cells do when they encounter their specific antigen?

Answer 6

When memory cells are established and encounter their specific antigen again, they leave blood at site of infection to enter tissues, become effectors and some then travel back to LN. Memory cells can live years, dividing infrequently.

Question 7

What are the two subsets of lymphocytes?

Answer 7

T and B

Question 8

Where do B cells mature?

Answer 8

Bone marrow or the bursa of fabricius

Question 9

Where do T cells mature?

Answer 9

In the thymus

Question 10

What do B cells do when they encounter their antigen?

Answer 10

Antibody secreting cells (plasma cells)

Memory cells

Question 11

What do T cells do when they encounter their antigen?

Answer 11

memory cells
Cytotoxic T lymphocyte (CD8+ Tc)
Helper T lymphocyte (CD4+ Th)
T regulatory cells

Question 12

What MHC class are CD8+ Tc ?

Answer 12

MHC class 1 restricted

Question 13

What MHC class are Th CD4+ cells?

Answer 13

MHC 2 restricted

Question 14

What are the subtypes of Th CD4+?

Answer 14

Th1, Th2 and Th17

Question 15

What cytokines do Th1 produce?

Answer 15

Th1 cytokines include IFNg and TNFa to activate macrophages and mediate delayed type hypersensitivity

Question 16

What cytokines do Th2 produce?

Answer 16

Th2 cytokines promote the differentiation of B cells into antibody secreting plasma cells, include IL-4, IL-5

Question 17

What cytokines do Th17 produce?

Answer 17

TH17 cells secrete IL-17 which is important in neutrophil recruitment, fungal infection and autoimmunity (identified in mammals)

Question 18

What is the role of Th1 cells?

Answer 18

Activate effectors (CTL) to kill intracellular pathogens

Question 19

What is the role of Th2 cells?

Answer 19

Stimulate B cells antibody production and class switching

Question 20

What do Tregs express on their surface?

Answer 20

CD25+ and FoxP3+ transcription factor

Question 21

What cytokines do Tregs produce and what is their role?

Answer 21

IL-10 and TGFbeta

Regulate the immune response and crucial in developing tolerance

Question 22

What type of response does TB generate?

Answer 22

A cellular response, so in TB IFNg can be detected in the blood

Question 23

What is an epitope?

Answer 23

A localized region on the surface of an antigen capable of eliciting an immune response and of combining with a specific antibody to counter that response.

Question 24

Each T or B lymphocyte is specific for…

Answer 24

a single antigenic epitope

Question 25

Each T or B lymphocyte is specific for...

Answer 25

a single antigenic epitope

Question 26

The diversity of antigens which T or B cells can recognize is explained by

Answer 26

T cell receptor (TCR) or BCR (surface membrane immunoglobulin). The diversity of the TCR and BCR can alter through mutations in the genes encoding these receptors.

Question 27

How can TCR on T cells recognise antigens?

Answer 27

TCRs on T cells must have antigen presented to them by MHC class I or II molecules on other cells

Question 28

How can BCR on B cells recognise antigens?

Answer 28

BCRs or surface immunoglobulin on B cells can bind antigen directly

Question 29

If pathogens infect a cell how is this recognised on the surface of the cell?

Answer 29

Peptides from the pathogen will be presented on the surface within the groove of the MHC class I molecule.

Question 30

How does endogenous antigen processing occur within the host cell?

Answer 30

Endogenous processing involves antigen entering cytoplasm where it is tagged with ubiquitin, enters proteasome where proteins are degraded into peptides. These are transported to the endoplasmic reticulum where they associate with MHC class I. This complex then moves through the Golgi to be expressed on the cell surface.

Question 31

What will happen when a CTL recognises an endogenously presented peptide/MCH complex?

Answer 31

Engagement will occur between the CTL’s TCR and CD8 molecules. As a result the infected cell will be lysed. The CTL will also secrete cytokines (IFNg) which enhance activation and recruitment of other CTL. The CTL will only recognize the peptide if it is presented by MHC class I. As a result the T cell is described as being MHC class I restricted.

Question 32

Which cells possess MCH 1, what does this mean?

Answer 32

MHC class I is present on virtually all nucleated cells in the body, so virtually any cell can present peptide antigen to CTL.

Question 33

How are pathogen peptides presented with MHC2?

Answer 33

``` Exogenous antigen processing Antigen presenting cells (macrophage, dendritic cell, B lymphocyte) which endocytose pathogens will process the antigen and present peptides on the cell surface within the groove of the MHC class II molecule ```

Question 34

What types of pathogen have exogenous antigen processing?

Answer 34

Infectious (bacteria, viruses, fungi, protozoa, helminths) | Environmental (pollen, dust mites, food)

Question 35

What does MHC class 1 present its antigen complex to?

Answer 35

T Cytotoxic cells

Question 36

What does MHC class 2 present its antigen complex to?

Answer 36

T helper cells

Question 37

B cells can bind soluble antigen with high affinity, what happens when this occurs?

Answer 37

Binding of antigen to the B cell stimulates proliferation of B cells. Ultimately B cells differentiate into lymphoblast and plasma cells. Plasma cells secrete immunoglobulin, which can also bind antigen directly

Question 38

How can activated B cells act as APC's?

Answer 38

Activated B cells can also act as antigen presenting cells to MHC class II restricted T helper lymphocytes, especially Th2 lymphocytes.

Question 39

What are the stages of clonal expansion?

Answer 39

Co-stimulation (multiple signals) Lymphocyte activation then division Multiple “clones” of identical antigen specific T or B lymphocytes

Question 40

What do you get if there is a lack of the complete clonal expansion cascade?

Answer 40

tolerance to the antigen

Question 41

How does co-stimulation in T cells occur?

Answer 41

Signal 1: Engagement of TCR with MHC and antigen. TCR can only recognise cognate peptide antigen in conjunction with MHC presented by APC Signal 2: Co-stimulation to stabilise contact between the APC & T cell e.g. CD4-MHC II or CD8-MHC 1 Signal 3: APC cytokines bind to T cell receptors Outcome: This induces intracellular signalling which drives the T cell to activation

Question 42

How does co-stimulation occur in B cells?

Answer 42

Signal 1: antigen binds to BCR (surface immunoglobulin) on B cells. The B cell processes the antigen and presents it on the surface with MHC class II Signal 2: The peptide-MHC complex is recognised by circulating, antigen specific T helper cells. These then co-stimulation the B lymphocyte via secretion of cytokines

Question 43

How is immunodeficiency different to tolerance?

Answer 43

``` Whole immune system is damaged & unresponsive Non specific (i.e. not restricted to one antigen) ```

Question 44

What is secreted by T cells that promotes proliferation?

Answer 44

IL-2

Question 45

What are the main outcomes of antigen presentation?

Answer 45

» antigen recognition by lymphocyte (>2 signals) » cytokine synthesis » lymphocyte activation » clonal expansion » development of effector T or B cells » development of T or B memory cells specific for that