Adaptive Immunity 2

Question 1

What are CD4+ and CD8+ cells?

Answer 1

CD8+ T-cells - posses direct cytotoxic activity towards cells infected with viruses, eliminate infections caused by intracellular pathogens or malignant transformation
CD4+ T-cells - regulatory cells which control the functions of other lymphocytes through cytokine secretion

Question 2

What are MHC1 and MHC2 molecules?

Answer 2

MHC1 molecules found on nucleated cells
Required to present intracellular antigens to recognise the virus infected cells, recognised by CD8+ cells

MHC2 molecules found only on antigen presenting cells
Required to present extracellularly derived antigen to recognise infected cells by CD4+ T cells

Question 3

What is self tolerance?

Answer 3

The autoimmune regulator (AIRE) is a transcription factor expressed in the medullary thymic epithelial cells (mTECs)
Through the action of AIRE, mTECs express tissue-restricted antigens and T cells that respond to those proteins are eliminated through cell death

Question 4

What occurs to T cells in cortex of thymus?

Answer 4

thymocytes undergo somatic gene recombination and positive selection by cTECs, only those T-cells which can recognise MHC with moderate affinity are allowed to migrate to the medulla (others die)

Question 5

What occurs to T cells in medulla of thymus?

Answer 5

thymocytes are screened for reactivity to tissue-restricted self antigens expressed by mTECs - negative selection

Question 6

Where does T cell activation occur?

Answer 6

in the peripheral lymphoid organs via antigen presentation by antigen presenting cells

Question 7

What are the 3 signals T cells require for activation?

Answer 7

Signal 1 - antigen-specific interactions
Signal 2 - co-stimulatory molecules
Signal 3 - instructive cytokines