SEROIM LEC ANTIBODY STRUCTURE AND FUNCTION

Antibody

- Product of B lymphocytes that undergo differentiation upon stimulation by antigen (plasma cells)

- reacts specifically with the inducing antigen in vivo and in vitro

Immunoglobulins

Antibodies are properly called as:

Glycoproteins

What are found in the serum portion of the blood?

Gamma band

electrophoresis @ pH 8.6

IgG, IgA, IgM, IgD, IgE

What are the 5 major classes of antibodies? (GAMDE)

Humoral immunity

Antibodies confer (is associated) with what type of immunity?

Antigen recognition

Opsonization

Activation of complement

Antibody essential roles: (3) (AOA)

Tetra peptide

What type of structure does immunoglobulin have?

H chains

2 large chains of immunoglobulin

L chains

2 smaller chains of immunoglobulin

Noncovalent forces

Disulfide interchain bridges

The chains of immunoglobulin are held by: (2)

Gerald Edelman and Rodney Porter

Who developed the basic structure of antibodies in 1950 and 1960s? (2)

Analytic centrifuge

To separate immunoglobulins based on molecular weight, what did Edelman use?

7S

The intact IgG molecule had a sedimentation coefficient of:

Svedberg unit

unit that indicates sedimentation rate

7M Urea

To obtain purified preparation of IgG to unfold the molecule, what did Edelman use?

Mercaptoethanol

What is the reducing agent that cleaved the exposed sulfhydryl bonds in Edelman's work?

3.5 S

After ultracentrifugation, the result was 2 fractions.

One fraction at ___________ with a molecular weight of 50000 Daltons and was designated as the H chain.

2.2 S

The other fraction with a Mol. wt. of 20000 daltons

designated as L chain

H2L2

What is the generalized formula for all immunoglobulins?

Papain

Porter's work on Igs is based on the use of proteolytic enzyme:

Papain

Enzyme used to cleave IgG into 3 pieces of about equal size

Each piece has 3.5 S

Carboxymethylcellulose Ion Exchange Chromatography

Porter used what type of chromatography to separate material in 2 fragments?

Fc fragment and Fab fragment

2 fragments separated by

Carboxymethylcellulose Ion Exchange Chromatography

Fragment crytallizable

•spontaneously crystallized at 4°C

•no antigen binding ability

•represents the carboxy terminal halves of the two H chains held together by S-S bonding

•important in effector function of Ig

Opsonization

Complement fixation

Fc fragment functions (2) (OpsC fragment)

Fragment antigen-binding

- have antigen binding capacity

- each fragment represents one antigen- binding

- 2 such fragments were present in an intact antibody molecules

1 L chain

1/2 H chain

Each Fab fragment consists of: (2)

Disulfide bonding

The Fab fragment's L chain and H chain are held together by:

Alfred Nisonoff

Used pepsin to obtain additional evidence for the structure of immunoglobulins

Pepsin

cleaved IgG at the carboxy-terminal side of the interchain disulfide bond

F(ab) squared and Fc

After cleaving IgG using pepsin, what are the results? (2)

F(ab) squared

One piece with all the antigen- binding ability

Fc

Similar to Fc except that it usually disintegrates into several smaller pieces

Bence Jones Protein

What protein is used for amino acid analysis of light chains?

Dr. Henry Bence-Jones

Discovered the BJP

Multiple myeloma

BJP are found in urine of patients with what disease?

60°C - Precipitate

80°C - Dissolve

BJP precipitate when heated to _________ but dissolve on further heating at __________

Kappa and Lambda

BJP analysis revealed 2 main types of L chains:

Constant region

Same sequence

Variable region

amino-terminal end of the immunoglobulin chain; part that recognizes antigen

Kappa L-chains

All ____________ have an almost identical carboxy-terminal end and the same is true of λ chains

Amino acid substitutions

The difference between the K and λ chains lies in the _________________ at a few locations along the chain

Only 1 type

In Igs, only how many types (Kappa or Lambda) can be present in a given molecule?

Heavy chain sequencing

Demonstrated the presence of domains similar to those of L chains

110 amino acids

The first how many amino acids at amino-terminal end constitute the variable domain?

Constant regions of the H chain

What part of the H chain gives each Ig type its name?

Gamma H chain

IgG heavy chain

Mu H chain

IgM heavy chain

Alpha chain

IgA heavy chain

Delta chain

IgD heavy chain

Epsilon chain

IgE heavy chain

Isotype

A unique amino acid sequence that is common to all immunoglobulin molecules of a given class in a given species

same heavy chain for each class

Allotypes

Minor variations of sequences that are present in some individuals but not to others (constant regions)

Kappa

Alpha

Gamma

Epsilon

Allotypes occur for which types of IgG? (4) (KAGE)

G1m3 and G1m17

Example of an allotype which are the variations of the Gamma chain?

Idiotypes

variations in variable regions

Variable regions

antigen recognition unit

constitute the idiotype of the mole

Hinge region

region that allows flexibility

Proline content

Hydrophobic residues

The hinge region is high in: (2)

Flexibility

• the ability to bend allows the two antigen-binding sites to operate independently

• assists in effector functions such as initiation of the complement cascade

Carbohydrate portion

In the hinge region, what is located between CH2 domains of the two H chains?

Balloon-shaped loops

The basic four-chain structure of all immunoglobulin is folded into compact globular subunits, based on the formation of _________________________ at each of the domains

Intrachain disulfide bonds

What stabilizes the globular regions?

Beta-pleated sheet

Within each of these regions or domains, the polypeptide chain is folded back and forth on itself to form a:

Immunoglobulin barrel

The folded domains of the H chains line up with those of the L chains to produce an:

WHERE ANTIGEN IS CAPTURED

Hypervariable regions

found within the variable regions of both heavy and light chains

Complementary determining regions

the acronym for CDR; names given to the hypervariable loops of the heavy chain in receptors in antibodies and lymphocyte receptors

Immunoglobulin Superfamily

molecular recognition or cellular adhesion

other proteins with three-dimensional structure similar to all immunoglobin

Immunoglobulin G

What is the predominant Ig in humans of about 75 to 80%?

23-25 days

half life of IgG

IgG1: 66%

IgG2: 23%

IgG3: 7%

IgG4: 4%

Percentages of the 4 major subclasses of IgG

IgG3

What is the IgG with the largest hinge region and the highest number of interchain disulfide bonds and most efficient at binding complement?

IgG2 and IgG4

Which IgGs have:

shorter hinge segments

poor mediators of complement activation

(2)

Providing immunity for newborn

Fixation of complement

Opsonization

Neutralization of toxins and viruses

Participation in agglutination and precipitation reactions

5 Major functions of IgG

(P-FON-P)

Macroglobulin

other name for IgM

10 days

half life of IgM

Immunoglobulin M

Mol. wt. of approximately 970,000

Immunoglobulin with the mu chain

Mu chain

mol. wt. 70,000

576 AAs; one more constant domain than γ chain

Pentameric form

The IgM has 2 forms, pentameric and monomer form.

Which is responsible for secretions?

Monomer form

The IgM has 2 forms, pentameric and monomer form.

Which is present on the surface of B cells?

Joining chain

Cysteine residues that serve as linkage points for disulfide bonds between two adjacent monomers

Holds the five monomeric units together

Star-like shape

Pentameric IgM shape with 10 functional binding sites

Crab-like

3d structure of IgM

What the structure looks like when combined with an antigen

Primary response antibody

The IgM is also called as this because it is the first to appear after antigenic stimulation and first to appear in the maturing infant.

True

T/F

IgM is synthesized only as long as antigen remains present

False, there are no memory cells for IgM

T/F

IgM has memory cells.

Primary response

Which response is predominantly IgM; long lag phase?

Secondary response

Which response is mainly IgG; shortened lag period; more rapid increase in antibody titer?

Complement fixation

Agglutination

Neutralization of toxins

Opsonization

Surface receptor for antigen

Functions of IgM (5) (CANOS)

Complement fixation

The most important function of IgM

Immunoglobulin A

immunoglobulin that migrates between gamma and beta regions on electrophoresis

has the alpha heavy chain

IgA1

primary monomer of IgA found in serum

IgA2

Secretory IgA

more resistant to bacterial proteinases (cleaved IgA1)

has disulfide bond that covalently link together the L chains rather than the H

serves to keep antigens from penetrating further into the bod

Dimer

What is the structure of IgA2?

Mucosal-associated lymphoid tissue

IgA2 is made in plasma cells found mainly in:

Secretory component

Later attached to the Fc portion of the α chains

Consists of five immunoglobulin-like domains

Derived from epithelial cells found in close proximity to the plasma cell

Makes dimer resistant to enzymatic digestion

Facilitate transport of IgA to mucosal surfaces

Specific receptor for IgA

3 functions of the secretory component of IgA

(MFS)

Patrol mucosal surfaces, first line of defense

Neutralization of toxins

Prevents bacterial adherence to mucosal surfaces

Functions of IgA (3) (PNP)

Sabin vaccine

Which vaccine demonstrates effectiveness of IgA's protective role on mucosal surfaces?