B&I immunity

Question 1

Describe T lymphocytes (3)

Answer 1

T = thymus

• Produce CD4 and CD8
• Mature to CD8 cytotoxic (~20% in blood) and CD4 helper (~80%)
• CD4 helper produces Th1, Th2, Th17

Question 2

What are the functions of the 3 subtypes of Treg CD4 helper T lymphocytes?

Answer 2

Regulate immune response:

• Th1 - cellular
• Th2 - antibody (humoral, makes B cells produce antibodies)
• Th17 - inflammatory

Question 3

What is the MHC?

Answer 3

“Major histocompatability complex” = set of highly polymorphic genes coding for HLA

Question 4

Describe the thymus (3)

Answer 4

• Primary lymphoid organ above the heart
• Largest at birth, shrinks with age
• Haemopoietic lymphoid precursors migrate from bone marrow to thymus to mature to T lymphocytes

Question 5

What is the function of cytotoxic T cells (CTL)

Answer 5

CTL react to your own cells when there is a change in MHC class I molecules (when they express a neo-antigen/viral or altered antigen

Question 6

What is MHC restriction? (3)

Answer 6

• MHC regulates viral immunity
• Viral immunity requires 2 antigens - SELF antigens coded by MHC, NON-SELF antigens coded by the virus (T cells only kill virally infected cells)
• Need 2 components together to get effective response against viral infection - recognition of viral immunity, is regulated by SELF component

Question 7

Describe MHC restriction at a molecular level (2)

Answer 7

• T cell receptor is a membrane bound Ig-like molecule on T lymphocytes
• HLA molecules (expressed on most cells) present peptide antigens to T cells (they are highly polymorphic)
  The two membranes form a synapse, a signal is conducted and the HLA cell goes into apoptosis

Question 8

What are human leukocyte antigens/HLA? (3)

Answer 8

• Antigens that express virus (MHC molecules)
• 6 different molecules expressed on human cells: class 1 - A, B, C (inside cell) // class 2 - DR, DP, DQ (extracellular)
• At each antigen there are 2 alleles expressed

Question 9

What are the properties of T-cell accessory molecules CD4 and CD8? (3)

Answer 9

• CD4 Helper T cells recognise antigens in MHC class 2 (bacteria)
• CD8 Cytotoxic T cells recognise antigens in MHC class 1 (virus)
• Both have tyrosine kinases in cytoplasmic tails that initiate T cell signalling through phosphorylation - crucial to immune activation

Question 10

What are the differences of MHC class 1 and 2? (3)

Answer 10

• MHC class 1: intracellular viral pathogens, CD8 cytotoxic T cells
• MHC class 2: extracellular bacterial pathogens, CD4 helper T cells
• Both classes of molecules have a peptide binding groove that holds a foreign peptide

Question 11

What is MHC polymorphism? (3)

Answer 11

• Amino acid sequences vary greatly - there are hundreds of variations at each MHC locus
• Express both maternal and paternal genes (total of 12 polymorphic molecules expressed on your cells - 2x6 molecules)
• No 2 people express same MHC (this is why you can’t transplant tissue from one person to another)

Question 12

What is the T cell receptor (TcR)? (2)

Answer 12

• Ig like membrane molecule

- Its gene locus is segmented and undergoes rearrangement