Immunology Chapter 4

Variable & Constant regions

Regions of antibodies

Polypeptides

Antibodies are composed of [?]

N termini

Top segment of the Y legs

Composed of a light and heavy chain

C termini

Bottom of the straight leg of the Y

Composed of heavy chains

Disufide bonds

Bonds that keep the variable and constant regions together

Carbohydrates

The number of [?] on the antibody determines what type of antibody it is

Fab Region

Part of antibody made of variable region of the legs of the Y

Fc Region

The constant region, made of half of the legs of the Y and the straight part

Hinge Region

Region denoting the bonds between each segment of the antigen

^K

λ

2 types of light chains

IgG

IgM

IgD

IgA

IgE

5 types of antibodies

Protein domains of about 110 amino acids

Ig chains are folded into compact & stable [?]

Folds in amino acid chain that bring sulfide groups together

Disulfide bonds formed by …

effector B cells (plasma cells)

Antibodies are produced by [?]

Hypervariable region of H chain V domain and L chain V domain

An Ag binding site is formed from the …

Multivalent

Multiple epitopes on pathogen surface

Univalent

1 epitope on pathogen surface

Polyvalent

Different kinds of epitopes

Increases chances for Abs to bind

Monovalent

1 type of epitope

Antigenic Determinant (epitope)

Part of the antigen that binds to Abs

Linear Epitope

Protein antigen that has all parts that bind to Ag right next to each other

Discontinuous Epitope

Protein antigen that has parts that bind to Ag separate from each other

Complementary structure

Weak noncovalent interactions (ionic bonds, hydrophobic interactions, van der Waals)

What holds the Ab and Ag together

Affinity

Sum of the non-covalent interactions between Ag and Ab

Clone of Ab producing cells

Monoclonal Abs are produced by ….

1. Fusion of B cells from mouse immunized with antigen + myeloma cells

• Myeloma stops antigen B cells from dying

2. Grow cells in drug-containing medium

3. Select for antigen-specific hybridoma

4. Clone selected cells

Creation of monoclonal Abs

Therapeutic Antibodies

• B cell cancers

• Breast cancer

Utility of Monoclonal antibodies

Germ Line Theory

Theory that the reason for the diversity of Abs is because we already have the genetic info that makes every type of antibody

Somatic Theory

Theory that the reason for the diversity of Abs is due to genetic variations throughout life creating antibody variability

Two Gene Theory

Theory that the reason for the diversity of Abs is due to multiple genes that can encode antibodies come together to create variability

V & J

Variable Light regions are created by [?] gene segments

V, D, & J

Variable Heavy regions are created by [?] gene segments

Random recombination

Produces diversity in Ag binding site of Ig

Germline DNA --somatic recombination→ VJ-joined rearranged DNA

Creation of Light chain

Germline DNA - somatic recombination→ DJ joined DNA -Somatic recombination→ VDJ-joined rearranged DNA

Creation of Heavy Chain

Enzymes

• RAG1 & 2

Signal sequence (RSS) - What the enzyme recognizes

• 1 turn & 2 turn

Gene recombination requires …

12

1 turn RSS have [#] base pairs

23

2 turn RSS have [#] base pairs

1.6 × 10⁶

Number of different Ab specificities

Heptamer

Nonamer

Flank RSS

Have to combine one 1 turn RSS & one 2 turn RSS

1 turn 2 turn rule (12/23 rule)

Diagram of chain regions

Removing gene segments between V, J, and D regions

RAGs cause gene recombination by,,,

1. P-Nucleotide

2. N-Nucleotide

3. Exonuclease Activity

3 mechanism of recombination enzyme driven Ab diversity

Hairpin at end of DNA segment

P Nucleotide Addition Site

1. Cleavage of hairpin

   1. Vertical

      1. Bases swings up/down

   2. Horizontal

      1. Bases stay where they are

2. Fill in complementary strands by DNA repair enzymes

Mechanism: P Nucleotide Addition

N Nucleotide Addition

Adds 1-15 base pairs randomly by TdT

Exonuclease Activity

Randomly removes nucleotides

Gaps filled by DNA synthesis and ligation to form coding join

Present in a region of the DNA that is being joined (V, D, or J)

Created by joining of regions

Complementarity-Determining Regions (CDRs) are either:

Differential RNA processing

Naive B cells get IgM and IgD on their cell surface with the same specificity through …

Where AAA (poly-A site) is

Where RNA is processed is determined by… which determines with type of Ab is expressed & if it is membrane-bound

P Nucleotide Addition

N Nucleotide Addition

Exonuclease Activity

Types of recombintion mechanisms

Somatic (hyper)Mutation

Process of further diversification of the whole of the V-domain after clonal selection

AID (Activated-Induced Cytidine Deaminase)

Enzyme that causes Somatic mutation

Made only by proliferating B cells

Converts cytosine into uracil

AID

Somatic mutation is mediated by [?]

Changes in affinity to epitopes

Mutating the hypervariable region causes…

Isotype Switching

Further DNA recombination events enable the rearranged V region coding sequence to be used with other heavy chain C genes

Switch Sites

Highly repetitive sequences that mediate recombination

AID and Switch Sites

Isotype Switching requires [?]

IgM

Pentameric

Best at complement Activation

IgA

Dimer

In mucosal tissue, Breast milk

Works to neutralize antigens

IgG

Highest in the blood

Involved in transplacental transfer from mother to baby

Involved in complement activation & antigen neutralization

IgE

Bound to most mast cells & basophils

Allergies