Immunology 146:474

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Immunology 146474

• Tu, Fri 1st period (840-1000 AM)
• Serc 118
• Dr. Lori Covey-Office hrs 1-3 Thursday
• Dept. of Cell Biology Neuroscience
• Nelson Hall, B314
• covey_at_biology.rutgers.edu
• Class web site http//lifesci.rutgers.edu/covey/
  Immuno/index.htm

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MHC Class I structure
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MHC Class I structure
b-pleated sheet
b-pleated sheet
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Structure of MHC class II molecules
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MHC Class II structure, contd
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MHC I/peptide MHC II/peptide
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Figure 3-23
NH2 terminus
NH2 terminus
COOH terminus
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Peptides eluted from two different MHC class I
molecules
Green residues are the anchor residues,
Ytyrosine, Fphenylalanine, both aromatic amino
acids
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Presentation of peptide bound by MHC class II
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Peptides that bind MHC class II molecules are
variable in length
Peptides are at least 13 amino acids long and can
be longer
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Figure 3-21 part 2 of 3
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T cell receptor binding to peptideMHC class I
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Figure 3-10
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Figure 3-14
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Specificity of a T cell receptor is defined both
by the peptide it recognizes and by the MHC
molecule bound to it
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Figure 5-17
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Figure 1-24 part 1 of 3
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Figure 1-24 part 2 of 3
Fc receptors
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Figure 1-24 part 3 of 3
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Figure 1-15
Macfarlane Burnet theory of clonal selection-1950s
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Mature B cells display membrane-bound
Immunoglobulin (antibody) molecules, which serve
as receptors for antigen. Each molecule of Ab on
the membrane of a single B cell has an identical
binding site for antigen.
Bone marrow, pre-B cells
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Interaction between antigen and the
membrane-bound antibody (mIg), as well as
interactions with T cells and macrophages,
selectively induces the activation and
differentiation of B-cell clones of corresponding
specificity. Selected B cells divide repeatedly
and differentiate over a 4-5 day period
generating a pool of plasma cells (terminally
differentiated) and memory cells.
2o lymphoid organs
Germinal centers
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To activate a B cell, it needs to receive a
signal from antigen recognition through the mIg
and a signal from CD4 T cells
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Figure 1-20
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Mature B cells display membrane-bound
Immunoglobulin (antibody) molecules, which serve
as receptors for antigen. Each molecule of Ab on
the membrane of a single B cell has an identical
binding site for antigen.
Bone marrow, pre-B cells
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Mechanisms for generating diversity
Number of total number of antibody specificities
available to an individual is known as the
antibody repertoire
Ig genes are rearranged in antibody-producing
cells Process called Somatic recombination
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A single B cell gives rise to a single antibody
molecule with two identical heavy and two
identical light chains A resting, naïve B cell
expresses IgM and IgD on its surface as its BCR
(B cell receptor).
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Southern blot analysis of V region and C
region. Digest DNA with restriction enzyme and
separate pieces of DNA in an electrical field.
Fragment of DNA
Labeled RNA representing Bence-Jones Protein
(light chains) Hybridized to DNA isolated From
either fibroblasts or B cells
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Organization of the Human Heavy chain variable
region loci
VH region
The Variable region of the Ig heavy chain is
encoded by three Gene segments The V segment
95-101 amino acids The D segment 2-5 amino
acids The J segment up to 13 amino acids
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VH region
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Organization of the Light Chain Loci
The Variable region of the Ig light chain is
encoded by two Gene segments The V segment
95-101 amino acids The J segment up to 13
amino acids
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Figure 4-4
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Figure 4-3
The heavy and light chain genes are located on
autosomes so there are 2 copies of the heavy
chain locus, 2 copies of the ? light chain and ?
light chain loci Possibility of generating 1011
antigen specificities
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• First mechanism that generates diversity
• Combinatorial Diversity
• Any functional VH segment can recombine with any
  DH segment and any JH segment
• Any functional VL segment can recombine with any
  JL segment

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Somatic recombination at the Ig heavy chain locus
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D--gtJ rearrangements on both alleles
VH DH JH C?
V--gtDJ rearrangement
VHDJH C?
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Figure 3-6
Framework and hypervariable regions define the
Variable Regions of the Ig heavy and light chain
polypeptides
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Recombination Recognition Sequences (RSS)
Only RSS elements that have different spacer
lengths can recombine with each other
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Recombination Recognition Sequences (RSS)
Only RSS elements that have different spacer
lengths can recombine with each other
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Figure 4-6 part 1 of 2
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Figure 4-6 part 2 of 2
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Figure 4-7
Proteins required for carrying out recombination
called V(D)J recombinase
RAG I and II enzymes required For variable
region Somatic recombination Create
hairpins Which are cleaved. Terminal
deoxynucleotidyl transferase (TdT) are added, nt
can be subtracted as well by nucleases
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Figure 4-7 part 3 of 3
2nd mechanism for creating diversity Junctional
Diversity Enzymatic processes creates Diversity
in the joint between gene segments
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Figure 4-8 part 1 of 3
Creates tremendous diversity at the joins of the
three segments
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Figure 4-8 part 2 of 3
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Figure 4-8 part 3 of 3
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Figure 4-7 part 3 of 3
3rd mechanism for creating diversity
Combinatorial- at the heavy and light chain
level Pairing of individual heavy chains with
different light chains
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Somatic hypermutations create diversity

• Occurs later after B cells are in secondary
  lymphoid organs
• Introduces single nt mutations into germline DNA
• Results in increased binding affinity of antibody
  for antigen

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4th mechanism for creating diversity Somatic
hypermutation Occurs after stimulation with
antigen in the antigen-dependent stage of B cell
differentiation
Introduces point mutations into the V regions of
the rearranged heavy- and light-chain genes at a
very high rate Requires a signal from CD4 T cells
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Somatic hypermutations create diversity
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Figure 4-9
Important enzyme involved in this process called
activation induced cytidine deaminase or AID
Requires transcription
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Figure 4-13
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T Cell Receptor (TCR)

• Comprised of two distinct chains, ? chain and ?
  chain, linked by S-S bond
• Each chain has a V region and a C region
• Carbohydrate-moeties
• Hydrophobic trans-membrane region

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Figure 4-11
T cell receptor gene rearrangement
Arranged in a similar pattern to Ig gene segments
and are rearranged by the same enzymes
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Figure 4-13
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Figure 4-14
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Figure 4-15 part 1 of 2
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Somatic recombination occurs at the TCR