3. Cell Antigen Recognition

Question 1

Phases of the adaptive immune response

Answer 1

Antigen recognition

• > Antigen presenting cell
• > Naive T lymphocyte
• > Naive B lymphocyte

Lymphocyte activation

• > Clonal expansion
• > Differentiation
• > Antobody producing cell + effector T lympocyte

Antigen elimination:
-> humoral immunity + cell mediated immunity -> elimination of antigens

Contraction (homeostasis)
-> Apoptosis

Memory
-> Surviving memory cells

Question 2

Adaptive immunity - Clonal selection

Answer 2

Lymphocyte Precursor

• > Genetic diversity BM/Thymus
• > Millions of clonal mature lymphocytes

A form of natural selection first proposed by Macfarlane Burnett in the early 1950s

Question 3

Ideal anti - invader plan

Answer 3

Diversity:
A single prgenitor cells gives rise to a large number of lymphocytes, each with a different specificity

Specificity:
Pool of mature naive lymphocytes

Expansion:
Proliferation + differentiation of activated specific lymphocytes to form a clone of effector cells

=> effector cells eliminate antigen

Question 4

Dealing with self - recognition

Answer 4

Diversity:
A single prgenitor cells gives rise to a large number of lymphocytes, each with a different specificity

Deletion (self - reactivity):
Removal of self - reactive immature lymphocytes by clonal deletion

Specificity:
Pool of mature naive lymphocytes
=> foreign antigen

Question 5

Clonal selection of B Cells

Answer 5

• > B cells that differ in antigen specificity (memory cells)
• > Antigen molecule with antigen receptor - antigen molecules bind to the antigen receptors of only one of the three B cells shown (plasma cells)

-> The selcted B cell profilerates, forming a clone of identical cells bearing receptors for the selecting antigen (plasma cells)

• > Antibody molecules - Some proliferating cells develop into long-lived memory cells that can respond rapidly upon subsequent exposure (memory cells)
• > Some proliferating cells develop into short-lived plasma cells that secrete antibodies specific for the antigen. (plasma cells)

Question 6

Antibodies

Answer 6

• > Antibodies bind to antigenic determinants
• > (portions of the antigen)

Virus binds to Antigen

Antigen with globular proteins

Question 7

Basic antibody structure

Answer 7

Immunoglobin

• 2 light chains
• 2 heavy chains
• disulfide bonds

Avidity vs Affinity

Question 8

Proteolytic cleavage by papain

Answer 8

amino terminus (top) + carboxy terminus (botom) => Fab (Fragment antigen binding) + Fc (Fragment crystalizable - effector portion)

Question 9

Proteolytic cleavage by pepsin

Answer 9

disulfide bonds + heavy chain => F(ab)2 + pFc

Question 10

1. Beta barrel

Answer 10

1. Light chain C domain
   - > Carboxyl terminus
   - > beta - strand
   - > disulfide bond
2. Light chain V domain
   - > amino terminus
   - > beta strands

Question 11

2. Immunoglobulin fold

Answer 11

Arrangement of beta strands

• > DEBA GFC
• > DEBA GFCC~

Question 12

Antibodies summary

Answer 12

• or Immunoglobulins (Ig)
• Glycoproteins
• Surface bound (B Cell Receptor)
• Free in solution
• Bind antigen with high specificity
• 1 B cell – 1 Antibody specificity
• 5 distinct classes of Immunoglobulin

Question 13

IgG1

Answer 13

Antigen:

• > Fab - light chain (212 residues)
• > Fc - heavy chain (450 residues)

Question 14

IgM

Answer 14

• > J - chain
• > VH
• > Cu 1 / 2 / 3 / 4

Question 15

Antibodies - Key facts

Answer 15

IgG – major serum component of serum Ig; important in secondary response

IgA – most prevalent in seromucosal secretions; commonly as dimer with secretory component

IgM – pentameric; first class of Ig to be produced; efficient activator of complement

IgD – B cell surface-bound form; signalling

IgE – Long heavy chain; parasite infectio

Question 16

Extra complexity

Answer 16

Somatic hypermutation
=>  is a cellular mechanism by which the immune system adapts to the new foreign elements that confront it (e.g. microbes), as seen during class switching

Isotype switching
=> is a biological mechanism that changes a B cell’s production of immunoglobulin from one type to another, such as from the isotype IgM to the isotype IgG.