CHAPTER III – ANTIBODIES Flashcards
Glycoproteins that recognize and bind to a particular antigen with very high specificity.
ANTIBODIES
Made in response to exposure to the antigen.
ANTIBODIES
One virus or microbe may have several (?), to which different antibodies may bind.
antigenic determinant sites
Each antibody has at least two identical sites that bind
antigen: Antigen binding sites.
Belong to a group of serum proteins called
Immunoglobulins (Igs).
Electrophoresis at pH 8.6, immunoglobulins appear primarily in the
gamma band
GENERAL FUNCTIONS OF IMMUNOGLOBULINS
Neutralize toxic substances
Facilitate phagocytosis and kill microbes
Combine with antigens on cellular surfaces and thereby cause the destruction of these cells either extravascular (outside of the blood vessels within the mononuclear-phagocyte system or reticuloendothelial system) or intravascularly (within blood vessels though the action of complement)
postulated that certain cells had specific surface receptors for antigen
Paul Ehrlich
Occurred once antigen was introduced, it would select the cell with proper receptor, combination would take place and receptors would break off and enter the circulation as antibody molecules
EHRLICH’S SIDE-CHAIN THEORY
New receptors would form in place of those broken off and enter the circulation as antibody molecules
EHRLICH’S SIDE-CHAIN THEORY
Receptors are located on the surface of the Ab-producing cell
EHRLICH’S SIDE-CHAIN THEORY
Felix Haurowitz
TEMPLATE THEORY
Antibody producing cells are capable of synthesizing a generalized type of antibody, and when contact with an antigen occurs, the antigen serves as a mold or template and alters protein synthesis so that antibody with a specific fits is made
TEMPLATE THEORY
This now specific antibody enters the circulation, while the antigen remains behind to direct further synthesis
TEMPLATE THEORY
MOST ACCEPTED
CLONAL SELECTION
Niels Jerne and Macfarlane Burnet independently supported the idea of clonal selection process for antibody formation
CLONAL SELECTION
The key premise is that individual lymphocytes are genetically programmed to produce one type of immunoglobulin and that a specific antigen finds or selects those particular cells capable of responding to it, causing to proliferate
CLONAL SELECTION
A flexible Y-shaped molecule with four protein chains
Monomer
Monomer four protein chains
2 identical light chains
2 identical heavy chains
1 LC, 2 HC = 4 Protein Chains
Two sections at the end of Y’s arms – Antigen binding sites (Fab).
Variable Regions
Identical on the same antibody, but vary from one antibody to another.
Variable Regions
Stem of monomer and lower parts of Y arms.
Constant Regions
For Complement fixation, Skin Fixation and Placental transfer
Fc region
first approximately 110 amino acids at the amino-terminal end the remaining amino acids can typically be divided up into three or more constant regions with very similar sequences, designated CH1, CH2, and CH3.
Variable domain of the H chain
are unique to each class and give each immunoglobulin
Constant regions of the H chain
: IgG
: IgA
: IgE
: IgD
: IgM
gamma H chain: IgG
alpha H chain: IgA
epsilon H chain: IgE
delta H chain: IgD
mu H chain : IgM
ANTIBODY VARIATIONS
ISOTYPE
ALLOTYPES
IDIOTYPE
Refers to the heavy chain that determine the Ig class
ISOTYPE
most common type
ISOTYPE
Minor variations of in the constant region
ALLOTYPES
E.g occur in the four IgG subclasses, in one IgA subclass, and in the kappa light chain.
Allotypes
Variations in variable regions
IDIOTYPE:
The aminoterminal ends of both L and H chains contain these regions, which are essential to the formation of the antigen-binding site.
IDIOTYPE
Possess both constant and variable regions
LIGHT CHAINS
o Kappa (65%)
o Lambda (35%)
o 2:1
LIGHT CHAINS
discovered through Bence Jones Proteins which are light chains produced by a malignant plasma cell from the urine of Multiple Myeloma pts
LIGHT CHAINS
Connect heavy and light chains
Connect light chains and light chains
Connect heavy chains and heavy chains
DISULFIDE BONDS
Between CH1 and CH2
HINGE REGION
Flexible region
HINGE REGION
Amino acid: PROLINE
HINGE REGION
Regions or sections in an Ig molecule
DOMAINS
A. 1 Light Chain
B. 1 Heavy Chain
C. IgM and IgE: with Extra CH4
1 Light Chain
2 domains: 1 VL and 1 CL
1 Heavy Chain
4 domains: 1 VH and 3 CH
: with Extra CH4
IgM and IgE
cleaves the Ig above the hinge region
Papain digestion
3 fragments
2 Fab + 1 FC
Papain digestion
cleaves Ig below the hinge region
Pepsin digestion
2 fragments
F(ab)2 + Fc
Pepsin digestion
BASIC Ig Structure
MONOMER
IgG, IgD, IgE, IgA (most)
MONOMER
2 binding site (2 valence)
MONOMER
Secretory component or piece of IgA2
DIMER
prevents the enzymatic degeneration of enzyme among secretions
DIMER
4 valence
DIMER
With J chain
DIMER
POLYMER
> 2 monomer
POLYMER
IgM
POLYMER
10 valence
POLYMER
Predominant type of immunoglobulin in humans
IgG
Greatest in serum concentration
IgG
(followed by IgM, IgA, IgD, IgE)
Longest half-life of any immunoglobulin class
IgG