Tolerance

Question 1

What is self-tolerance?

Answer 1

Inability to make antibodies against own macromolecules (i.e. not recognising self-antigens)

Question 2

When are lymphocytes exposed to self-antigens?

Answer 2

When they’re developing

B cells in bone marrow
T cells in thymus

Question 3

What happens when developing B cells encounter self-antigens?

Answer 3

Clonal deletion - cells die off

Build receptor tolerance through daily encounter with antigen

Question 4

What happens when developing T cells recognise self-antigens?

Answer 4

Negative selection - cells recognising self-antigens die (clonal deletion)

Positive selection - only cells recognising MHC cells survive

Question 5

What is peripheral tolerance?

Answer 5

Once lymphocytes have developed and entered the periphery, they can be eliminated by regulatory T cells if they recognise self-antigens

Question 6

What is positive selection of T cells?

Answer 6

Only cells recognising MHC survive

Question 7

What is negative selection of T cells?

Answer 7

Cells recognising self-antigens die (clonal deletion)

Question 8

What happens if negative selection of T cells die?

Answer 8

1. Chance that co-stimulation fails (anergy)
2. Self-recognising CD8+ T cells start attacking cells
3. Self recognising CD4+ T cells could cause positive selection of a maturing B cell in lymph node –> maturing B cell makes self-recognising antibodies

Question 9

How does reproductive system provide acquired tolerance? Why is this tolerance important?

Answer 9

An immune activation against the foetus needs to be avoided

Foetal material (sperm, egg etc) lack MHC I and II so that no antigens are presented and no immune response can be initiated

Question 10

How do cells in reproductive system further suppress immune response?

Answer 10

Cells produce more than normal amounts on glycoproteins present on cell membrane –> even if antigen presentation occurs, lymphocyte activation is surpassed as antigen cannot be reached