Immune System 3

Question 1

B cell activation and antibody production ?

Answer 1

• mature B cells enter a secondary lymphoid tissue
• in absence of its sepcific antigen, the B cells leave the lymph node and recirculate
• Naive B cells encounter an antigen
  in a secondary lymphoid tissue
• when this happens, antigen-specific B cells are futher activated by T helper cells
• some activated B cells proliferatein primary follicle + differentiate in plasma cells (secrete IgM)

Question 2

What happens to activated B cells after they migrate to secondary lymphoid follicles?

Answer 2

• mature more slowly
• after diffferentiation they tranform into plasma cells secreting high-affinity antibodies (IgG, IgA)
• also develop into **memory B cells **
• activation of memory cells produces quicker + stronger response

Question 3

structure of T cell receptor (TCR)?

Answer 3

• made of 2 polypeptide chains chains α and β
• each chain has variable + constant regions
• each V chain contains 3 CDRs
• TCR complex also includes CD3 complex proteins and the ζ chain(zeta), which are required for signal transduction.

Question 4

What are the key differences between MHC class I and class II molecules?

Answer 4

• different structures and expression patterns
• present polypeptides from different sources

Question 5

What are the two types of MHC molecules and their key differences?

Answer 5

• MHC class I = expressed on all nucleated cells
• binds TCR of CD8+ T cells
• MHC class II = expressed on APC
• binds TCR of CD4 T helper cells

Question 6

Why are MHC molecules important in immune response?

Answer 6

• MHC molecules are polymorphic, meaning they have many genetic variants, which play a role in transplant rejection and diversity in immune responses.

Question 7

How are endogenous antigens presented to CD8+ T cells?

Answer 7

• intracellular endogenous antigens are presented by MHC class I molecules
• antigens must be procesed into peptides before binding MHC
• MHC Class I molecules present the peptide on the cell surface (all nucleated cells have MHC-I molecules)
• CD8+ cytotoxic T cells recognize the antigen and can kill the infected cell.

Question 8

How are exogenous antigens presented to CD4 T helper cells ?

Answer 8

• Exogenous (extracellular) antigens are internalised and
  presented by MHC class II
• proteins must be processed to peptides before binding MHC
• The MHC Class II-peptide complex is presented on the surface of the APCs for recognition by CD4+ T helper cells.

Question 9

Similarities + differences in T + B cell development ?

Answer 9

• Both originate from bone marrow stem cells.
• Both rearrange receptor genes to produce a unique receptor (TCR for T cells).
• Both express a pre-receptor before full maturation.
• Both undergo negative selection to eliminate self-reactive cells.
• T cells develop in the thymus, not the bone marrow.
• T cells undergo positive selection (eliminate non-functioning cells)

Question 10

What can an immature T cell recognize when it leaves the bone marrow and migrates into the thymus?

Answer 10

• Can recognise self MHC and respond to
  a foreign peptide (defence)
• Can recognise and respond to self MHC
  plus self peptide (danger!) = negative selection
• No recognition of self-MHC (useless) = positive selection

Question 11

What happens during positive selection of T cells ?

Answer 11

• selects T cells that can recognize self-MHC and has a TCR that can bind to self-MHC molecules
• Occurs when the TCR of double-positive
  (CD4+CD8+) T cells recognise MHC
  molecules expressed on cortical epithelial
  cells
• Only 1 - 2% capable of recognising
  own MHC will be selected
  – Vast majority of T cells with non-
  binding TCR die via apoptosis