4 : ANTIBODIES / IMMUNOGLOBULINS

Immune system

functions to protect the body and fight off infection

Immunoglobulin

other term for antibody and gamma globulins

these molecules are specialized globular proteins that play a vital role in immunity

are glycoproteins that are composed of 86% to 98% polypeptide and 2% to 14% carbohydrate

Antigen recognition

there is direct binding between the intact antigen and antibody

Opsonization

function to hasten or enhance phagocytosis

8.6

pH level at which most serum proteins can be separated

Heavy-Chain sequencing

largen chain of the molecule

extends the full length

MW : 50,000 - 70,000 D

The nature of light chains

smaller chain of the antibody

found on all types of immunoglobulin molecules but do not extend the full length

only has 1 variable and 1 constant region

MW : 22,000 D

Variable region

located in the amino terminal end of the antibody molecule

defines the specificity of an antibody

first 110 amino acids

Constant region

found on the carboxy terminal end of the antibody

starts from the 111th amino acid onwards

1950-1960

the basic structure of the antibody was first described during this time

Gerald Edelman & Rodney Porter

first described the structure of the antibody

made use of the IgG antibody for their research because it is the most prevalent in the body

Gerald Edelman

Separate out immunoglobulins on the basis of molecular weight using the analytic ultracentrifuge

found out that an intact IgG molecule had a sedimentation coefficient of 7s

Sedimentation coefficient

used to characterize a behavior of a molecule in sedimentation process, notably, centrifugation

Rodney Porter

based on the use of the proteolytic enzyme, papain, which was used to cleave IgG into three pieces of equal size

Papain cleavage

cleaves the IgG or the antibody molecule below the set of disulfide bonds that holds the 2 heavy chains together that would result in the formation of 3 fragments

antigen sites are separated out and the only intact region is the Fc region

results to a loss of the ability to agglutinate because the binding sites are separated out and is not enough to cause agglutination

Alfred Nisonoff

used pepsin to cleave IgG at the carboxyterminal side of the interchain disulfide bonds, yielding one single fragment

Fc Fragment

stands for crystallizable fragment

crystallizes at 4 C

represent the carboxy-terminal halves of the two H chains which are all constant regions

no antigen binding capacity

responsible for the biological activity of the molecule

Fab Fragment

Fragment Antigen Binding

function is antigen binding

1 light chain and half of the heavy chain held together by disulfide bonds

Hinge region

the segment of heavy chain located between the CH1 and CH2 regions

rich in hydrophobic residues and has high proline content

susceptible to proteolysis because of the presence of disulfide bonds

Carbohydrate portion

attached in the CH2 domain

increasing the solubility of immunoglobulin

enhancing functional activity of the Fc domains

Hypervariable regions

also called complementarity determining regions

responsible for the diversity of immunoglobulin molecules

IgG

IgM

IgA

IgE

IgD

types of antibody classes

IgG

major immunoglobulin in normal human serum

the only immunoglobulin that crosses the placenta because of its smaller size

also found in cord blood and CSF

has a high diffusion coefficient

past or recurring infection

70 - 75%

IgG comprises approximately ?

Half-life

is a measure of the mean survival time of the antibody molecule following their formation

IgG3

longest hinge region

IgG2

shorter hinge region than IgG1

IgM

referred to as macroglobulin

agglutinating immunoglobulin

largest of all immunoglobulin classes

3rd most abundant immunoglobulin

considered as primary response antibody

detected during acute or current infections

5-10%

IgM comprises approximately ?

Pentameric form

found in the serum

secreted by the plasma cells

has CH4 as an extra domain

Monomeric form

exists as a single antibody molecule with a longer heavy chain

expressed as membrane-bound antibody on the surface of B-cells

IgA

the predominant immunoglobulin in secretions

functions to protect your mucosal surfaces

is usually found in tears, saliva, milk, colostrum & intestinal fluids

2nd most abundant

10-15%

IgA comprises approximately ?

IgA1 / Monomeric IgA

found mainly in the serum

MW : 160,000 D

exists as a single immunoglobulin molecule

responsible for antigenic clearance and immune regulation

IgA2 / Dimeric IgA

predominant form in secretions

also appears in breast milk, colostrum, saliva, tears, and sweat

has a secretory component in the middle which makes the dimer more resistant in proteolytic digestion

Secretory component

a protein derived from epithelial cells found in close proximity to the plasma cells

act to facilitate transport to IgA to mucosal surfaces

makes the dimer more resistant to proteolytic damage by masking the sites that would be susceptible to protease cleavage

IgD

first discovered in 1965

is extremely susceptible to proteolysis because of its very long hinge region

mostly found on the surface of immunocompetent but unstimulated B lymphocytes

less than 0.001%

IgD comprises approximately ?

IgE

least abundant in the immunoglobulin pool

most heal labile / sensitive to heat

does not participate in typical immunoglobulin reactions like complement fixation, agglutination, or opsonization

mediates hypersensitivity reactions, allergies, and anaphylaxis

0.0005%

IgE comprises approximately ?

150,000

molecular weight of IgG

900,000

Molecular weight of IgM

160,000

molecular weight of IgA

180,000

Molecular weight of IgD

190,000

Molecular weight of IgE

Isotypes

unique amino acid sequences that are common to all immunoglobulin molecules of a given class or subclass

refer to variations between light and heavy chains defined by constant regions of all antibodies and kappa and lambda light chains

Allotypes

refers to the differences in the constant regions of both the heavy and light chains

occur in the four IgG subclasses, in one IgA subclass and in the light chain

minor variations of amino acids sequences that are present in some individuals of the same species but not others

Idiotypes

variations in the variable region that give each immunoglobulin molecule its specificity

contained in the amino-terminal ends of both L and H chains

Primary antibody response

occurs when an antigen comes in contact with the immune system for the first time

Antibody is IgM

Lag phase

no antibody is detectable yet because the body is still learning how to recognize the antigen

Log phase

there is an increase in antibody titer

antibody has a logarithmic increase

Plateau phase

the antibody titer is stable

Decline phase

the antibody is catabolized and the titer starts to decrease

Antibody titer

a measurement of how much antibody an organism has produced that is able to recognize a particular epitope

expressed as the inverse of the greatest dilution that shows a positive result

Secondary antibody response

the immune system can eliminate the antigen which has been encountered by the individual during primary response more rapidly and efficiently

this phase is already the subsequent exposure to the same antigenic stimulus

antibody is IgG

Affinity

measure of the binding strength of a single antibody-antigen interaction

Avidity

measure of the total binding strength

Hydrophobic bonds

Hydrogen bonds

Electrostatic forces

Van der Waals Forces

4 TYPES OF BONDS

Hydrophobic bonds

when an antigen and antibody molecules come together, these sidechains interact and exclude water molecules from the area of interaction

Hydrogen bonds

formation of hydrogen bridges between two electronegative atoms

Electrostatic forces

results from the attraction of oppositely charged amino acids located on the side chains of two amino acid residues

Van der Waals forces

nonspecific, attractive forces generated by the interaction between electron clouds and hydrophobic bonds

Georges Kohler and Cesar Milstein

discovered a technique to produce antibodies arising from a single clone or a single B-cell

Monoclonal antibody

defined as identical antibodies that are produced from a single clone of plasma cells

Hybridomas

fusion of two different type of cells: Myeloma cells, Activated B-cell

Pregnancy testing

Detection of tumor antigens

Measurement of hormone levels

Therapeutic agents for autoimmune diseases

Clinical application of monoclonal antibodies