Genetic Models in
Immunobiology
,Introduction
Innate immunity:
• Physical barriers
• Already in plants
Adaptive immunity:
• Special to vertebrates
• Vaccination involves adaptive immunity
Components in interaction of innate and adaptive immunity:
• Dendritic cells: antigen-presenting to T-lymphocytes
• Macrophages
Lymphocytes:
• light microscope: small rim of cytoplasm
• B-lymphocytes → derived from bone marrow
• T- lymphocytes → derived from thymus
• B- & T-lymphocytes cannot be distinguished by light microscopy
Antigen-receptors on T- and B-lymphocytes:
• Extracellular antigen-binding domains
• Intracellular signaling domains
• Both lymphocytes express pre-versions of their
receptors
Clonal selection theory (Frank Macfarlane Burnet, 1957):
• Millions/billions of different receptor types
• Series of lymphocytes with different receptors
➔ Binding to specific antigen → Proliferation of this clone of cell
➔ Differentiation into effector cells
VDJ Recombination
Antibody: 150 kDa
• Antibodies recognize:
➔ Proteins
➔ Carbohydrates
➔ Small molecules – haptens (drugs, NP,
FITC etc.)
➔ Structures on cells, microbes and
viruses
• Structure of antibodies:
Hypervariable region in the V-domains form the antigen-combining site:
➔ Hypervariable (HV) regions are called CDRs (complementary regions)
➔ 3 CDRs in the heavy chain and 3 CDRs in the light chain
1
, VDJ-Recombination:
The organization of the immunoglobulin genes (human):
Generation of diversity (God) in the mouse:
• Somatic recombination of the variable gene segments and random combination of heavy and
light chains
• Heavy chain: app. 100 VH genes x 12 D genes x 4 JH genes → app. 4.800 combinations
• Light chain: app. 90 VL genes (90 Vκ and 3 V λ) x 4 JL genes → app. 360 combinations
• App. 2 x 106 different specificities (only?!)
Generation of further diversity by unprecise recombination:
• Recombination occurs in an undefined way → joining sequences are variable → N-
nucleotides inserted by TdT enzyme
• Recombination signal sequences RSS: 5´ - Heptamer – Spacer (12 or 23 bp) – Nonamer – 3´
• RSSs are never found in the translated protein → cleaved out
“Rules” for VDJ recombination:
• Only gene segments with different spacers can recombine: 12/23 bp rule
• E.g. Vκ (12mer RSS) with Jκ (23mer RSS) and VΗ (23mer RSS) with DH (12mer RSS)
• But not: VH (23mer RSS) with JH (23mer RSS)
Immunoglobulin and TCR loci:
• Promotors 5´of each V gene (and D gene)
• Enhancers enhance the expression and open up the gene locus for recombination
• Igκ V gene in both orientations → deletions or inversions are possible
2
Immunobiology
,Introduction
Innate immunity:
• Physical barriers
• Already in plants
Adaptive immunity:
• Special to vertebrates
• Vaccination involves adaptive immunity
Components in interaction of innate and adaptive immunity:
• Dendritic cells: antigen-presenting to T-lymphocytes
• Macrophages
Lymphocytes:
• light microscope: small rim of cytoplasm
• B-lymphocytes → derived from bone marrow
• T- lymphocytes → derived from thymus
• B- & T-lymphocytes cannot be distinguished by light microscopy
Antigen-receptors on T- and B-lymphocytes:
• Extracellular antigen-binding domains
• Intracellular signaling domains
• Both lymphocytes express pre-versions of their
receptors
Clonal selection theory (Frank Macfarlane Burnet, 1957):
• Millions/billions of different receptor types
• Series of lymphocytes with different receptors
➔ Binding to specific antigen → Proliferation of this clone of cell
➔ Differentiation into effector cells
VDJ Recombination
Antibody: 150 kDa
• Antibodies recognize:
➔ Proteins
➔ Carbohydrates
➔ Small molecules – haptens (drugs, NP,
FITC etc.)
➔ Structures on cells, microbes and
viruses
• Structure of antibodies:
Hypervariable region in the V-domains form the antigen-combining site:
➔ Hypervariable (HV) regions are called CDRs (complementary regions)
➔ 3 CDRs in the heavy chain and 3 CDRs in the light chain
1
, VDJ-Recombination:
The organization of the immunoglobulin genes (human):
Generation of diversity (God) in the mouse:
• Somatic recombination of the variable gene segments and random combination of heavy and
light chains
• Heavy chain: app. 100 VH genes x 12 D genes x 4 JH genes → app. 4.800 combinations
• Light chain: app. 90 VL genes (90 Vκ and 3 V λ) x 4 JL genes → app. 360 combinations
• App. 2 x 106 different specificities (only?!)
Generation of further diversity by unprecise recombination:
• Recombination occurs in an undefined way → joining sequences are variable → N-
nucleotides inserted by TdT enzyme
• Recombination signal sequences RSS: 5´ - Heptamer – Spacer (12 or 23 bp) – Nonamer – 3´
• RSSs are never found in the translated protein → cleaved out
“Rules” for VDJ recombination:
• Only gene segments with different spacers can recombine: 12/23 bp rule
• E.g. Vκ (12mer RSS) with Jκ (23mer RSS) and VΗ (23mer RSS) with DH (12mer RSS)
• But not: VH (23mer RSS) with JH (23mer RSS)
Immunoglobulin and TCR loci:
• Promotors 5´of each V gene (and D gene)
• Enhancers enhance the expression and open up the gene locus for recombination
• Igκ V gene in both orientations → deletions or inversions are possible
2
