Cell mediated immunity

Question 1

Describe primary and secondary lymphoid tissues

Answer 1

PRIMARY: where lymphocytes are generated/ matured (bone marrow, thymus)
SECONDARY: where lymphocytes interact with APC and immune responses are generated (spleen, MALT, BALT, LNs)

Question 2

Describe lymphocytes recirculation

Answer 2

• Naive lymphocytes constantly recirculating through blood/ lymph
• Recirculate until they come into contact with their specific Ag in the LN
• This then stimulates cell activation, division, lymph node enlarges, activated lymphocytes leave LN in the lymph before entering the blood via thoracic duct.
• Some form memory cells, they leave site of infection and enter tissues (effector cells) others migrate back to LN.

Question 3

Describe lymphocytes subsets

Answer 3

• B cells will differentiate into plasma cells (found in tissues)
• T cells = CD4+ (helper)or CD8+(killer)

Question 4

In birds where do B cells mature?

Answer 4

Bursa of Fabricius

Question 5

What is an MHC class 1 restricted T cell?

Answer 5

• CD8+/ CD4-= Cytotoxic

Question 6

What is the function of Th2 cells?

Answer 6

• To promote the differentiation of B cells into plasma cells
• Express IL4, IL-5

Question 7

What do regulatory T lymphocytes do?

Answer 7

Regulate immune response and have important role in tolerance
(Express IL-10 and TGFb)

Question 8

What is the Bovigram test?

Answer 8

• Cytokine synthesis by Th1 cells - test detects IFN-y in the blood

Question 9

Briefly describe the receptors found on lymphocytes

Answer 9

• T and B cell receptors recognise specific epitopes on antigens
• Tcell receptors (TCR) must have antigen presented to them by either MHC class 1 or 2. B cell receptors (BCR) can bind the antigen directly themselves.

Question 10

Which area of a TCR or CD3 has a signalling function?

Answer 10

The constant region
(Antigen binds to the top, activates signalling cascade through the constant region which leads to lymphocyte activation and proliferation)

Question 11

Which area of a TCR or CD3 has a signalling function?

Answer 11

The constant region
(Antigen binds to the top, activates signalling cascade through the constant region which leads to lymphocyte activation and proliferation)

Question 12

How is generation of diversity in lymphocytes achieved?

Answer 12

By somatic DNA recombination of different gene segments of the V region

Question 13

Describe the MHC class 1 pathway

Answer 13

• Virus infects cell, it is degraded and taken through ER to the golgi, peptides then presented via MHC class 1 molecules on surface of the APC to circulating cytotoxic T cell, TCR and CD8 molecule interact with MHC 1.

(MHC 2 pathway involves pathogen being endocytosed or binding direct to B cell)

Question 14

Describe exogenous antigen uptake

Answer 14

• MHC class 2 restricted
• Infectious e.g. bacteria/ fungi/ viruses
• Environmental (pollen, dust mites, food)
• Opsonised agents
• Enters host cell endosomes by phagocytosis and pinocytosis
• Can also enter by APCs PRR recognition of PAMPS on microbes and binding to BCR on B cells.

Question 15

Which antigen uptake rquires ubiquitin?

Answer 15

Endogenous- antigen enters cytoplasm and is tagged with ubiquitin.

Question 16

What is the role of B cells?

Answer 16

To secrete antibodies which have a functional effect

• Ab bind directly to pathogens: prevents pathogen infecting host cells
• Ab binds to pathogen with Fc region protruding (Fc recognised by Fc receptor on granulocytes, enhancing phagocytosis)
• Membrane Ab binds to pathogen and is endocytosed by B cell (then presented to Th cells)

Question 17

What is the main difference between B cells and plasma cells?

Answer 17

• In B cells antigens bind directly to the BCR on surface

- In plasma cells they can secrete antibodies which then bind directly to antigen.

Question 18

Describe polyclonal antibodies

Answer 18

-Found in serum, contain multiple clones of plasma cells and antibodies against multiple epitopes are secreted. Can be used for passive transfer of Ig into neonates and in diagnostic tests.

Question 19

What is the importance on monoclonal antibodies?

Answer 19

• They can be used therapeutically by binding them to cancer cells, this hybrid cell is immortal and produces an antibody that recognises a single epitope.

Question 20

What are co-stimulation molecules?

Answer 20

-Needed to activate the cascade to trigger lymphocyte activation and division. In absence of this you get a tolerance to the antigen.

Question 21

Describe co-stimulation of T cells

Answer 21

• 3 signals needed
• 1st= engagement of TCR with MHC and antigen
• 2nd= to stabilise contact between APC and T cell (e.g. CD4 -MHC 2)
• 3rd= APC cytokines bind to T cell receptors amplifying activation.

Question 22

Describe co-stimulation in B cells

Answer 22

-2 signals needed
-1st= Ag binds to BCR, B cell then presents it on surface with MHC class 2
2nd= peptide-MHC complex recognised by Th cell which co-stimulate B lymphocytes by secretion of cytokines.

Question 23

Why does immunodeficiency differ from tolerance?

Answer 23

• NOT antigen specific

- Immune system is damaged and unresponsive