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
Predominant in chronic phase of infection and in recovery
IgG
Its subclasses are differentiated in the number of disulfide bonds
IgG
- predominant (67%); 2 disulfide bonds
IgG1
- 22%; 4 disulfide bonds
IgG2
- 7%; 15 disulfide bonds
IgG3
- 4%; 2 disulfide bonds
IgG4
FUNCTIONS OF IgG
Provides immunity to the newborn by crossing thru the placenta (Most Efficient: IgG1)
Fixes or activates complement (Best: IgG3)
Opsonization
Neutralization of toxins and viruses
Participation in agglutination and precipitation reaction
crossing thru the placenta (Most Efficient:)
IgG1
Only Ig to cross the placenta
IgG
First Ab present/found in newborns
IgG
Fixes or activates complement (Best:)
IgG3
FUNCTIONS OF IgM
Complement fixation: Most efficient in triggering the classical complement pathway
Best agglutinin
Opsonization
Neutralization of toxins
FUNCTIONS OF IgD
Responsible for IMMUNOREGULATION
DISEASE ASSOCIATIONS OF IgG
o Infectious diseases, such as hepatitis, rubella, and infectious mononucleosis
o Collagen disorders, such as rheumatoid arthritis and systemic lupus erythematosus
o Hematologic disorders, such as polyclonal gammopathies, monoclonal gammopathies, monocytic leukemia, and Hodgkin’s disease
DISEASE ASSOCIATIONS OF IgM
o Infectious diseases, such as subacute bacterial endocarditis, infectious mononucleosis, leprosy, trypanosomiasis, malaria, and actinomycosis
o Collagen disorders, such as scleroderma
o Hematologic disorders, such as polyclonal gammopathies, monocytic leukemia, and monoclonal gammopathies (e.g., Waldenström’s macroglobulinemia)
DISEASE ASSOCIATIONS OF IgA
o Infectious diseases, such as tuberculosis and actinomycosis
o Collagen disorders, such as rheumatoid arthritis
o Hematologic disorders, such as polyclonal gammopathies,
o Monocytic leukemia, and monoclonal gammopathy (e.g., IgA myeloma)
o Liver disease, such as Laennec’s cirrhosis and chronic active hepatitis
Pentamer in serum; Monomer as a surface marker
IgM
Free state: Star-like appearance
IgM
Combined with Ag: crab-like appearance
IgM
Known as the macroglobulin
IgM
Most primitive
IgM
First to appear in phylogeny and the last to leave in senescence
IgM
First to appear/be made by infants
IgM
FIRST to appear after a primary antigenic stimulus
IgM
IgM GRAM NEGATIVE bacteria Example:
Wasserman antibodies, heterophile antibodies, RF (Rheumatoid factor), cold agglutinins and allohemagglutinins belong under this type of antibody
Formed in response to stimulus by GRAM NEGATIVE bacteria
IgM
Monomeric in (IgA1)
serum
Occurs as a dimer (IgA2) in
secretions
Secretory Component provides:
Mucosal Immunity
Mucosal Immunity
Prevents attachment of pathogen to mucosal surface
Prevent enzymatic degradation of IgA
Found on unstimulated but immunocompetent cell
IgD
Postulated as anti-idiotypic antibody involved in a feedback mechanism to switch off B-CELLS
IgD
Location: on the surface of a B lymphocyte in association with IgM
IgD
Least abundant immunoglobulin in the serum
IgE
Heat-labile antibodies, originally called as Reagin antibody
IgE
Binds strongly to a receptor on mast cells and basophils and together with antigen, mediates the release of histamine and heparin from these cells
IgE
Mediates hypersensitivity reactions, such as allergies, and anaphylaxis, and generally responsible for an individual’s immunity to invading parasites
IgE
Eosinophil recognizes the IgE attached to parasite to release Major Basic protein and Eosinophil Cationic Protein
IgE
Multiple epitopes per
one antigen
Depends on the (?) to which an epitope is more specific
antibody
Apply electricity in the serum to check for migration at pH 8.6 (alkaline)
Electrophoresis
Electrophoresis proteins
- Albumin – primary
- Alpha-proteins
- Beta-proteins
- Gamma-proteins – Immunoglobulins
Once Ab binds with Ag, Ag cannot create a toxic effect
Neutralize toxic substances
Some Ig can act as an opsonin
Facilitate phagocytosis and kill microbes
extravascular (outside of the blood vessels within the)
mononuclear-phagocyte system or reticuloendothelial system
intravascularly (within blood vessels though the)
action of complement
– antigen-binding site
Fab
fragment crystallizable or fragment constant
Fc
not capable of antigen-binding but can bind to cells (immune cells – B and T cells)
Fc
capable of binding or fixing the complement
Fc
each Ag has an Ab which alerts the immune system
Fc
T cell attaches to Ab → reticuloendothelial system
Extravascular
organs under RES:
o spleen – primary cell Apoptosis
o liver
Toxic and immediate destruction of the Ag
Intravascular
Stimulation of complement attaches to Fc portion leading to lysis
Intravascular
Receptors are located on the surface of the Ab-producing cell
EHRLICH’S SIDE-CHAIN THEORY
Different studies, the same idea
CLONAL SELECTION
Example: Hematopoiesis – formation of blood cells
CLONAL SELECTION
HSC – able to produce different CFUs
CLONAL SELECTION
Erythroid – rbc
Myeloid – granulocytes, monocytes, platelets
Lymphoid – B and T lymphocytes (B cell matures into a plasma cell once Ag is encountered; plasma cell produces Ab)
CLONAL SELECTION
1 LC, 2 HC =
4 Protein Chains
can filter urine
Bence Jones Proteins
Bence Jones Proteins
heated at 50-60oC →
heated at 100oC →
precipitates
dissolves
2 mols of sulfide
DISULFIDE BONDS
Complete antibody =
12 domains (2 LC [2x2] x 2 HC [4x2])
IgE =
14 domains (+2)
Cutting parts of Igs through enzyme treatment
FRAGMENTATION
Ags and Ig are monomer in nature
MONOMER
can bind 10 Ags at the same time
POLYMER
– larger complexes; particulate ag and ab
Agglutination
– smaller complexes, soluble ag, best precipitin or best Ab
Precipitation
Monomer
Too small to cause an agglutination rx
Participates with the use of an additional reagent – incomplete antibody
IgG
– smaller complexes, soluble ag, best precipitin or best Ab
Precipitation
↑ WBCs – abnormal in function
monocytic leukemia
Counterpart: Neutrophil
IgM
(counterpart: mast cells and basophils)
IgE Allergic reactions
(counterpart: eosinophils)
IgE Parasitic infections
Early onset or acute phase infection
IgM
More efficient than IgG3
IgM
Has a large structure – only needs 1 molecule of IgM to activate the complement (2 mols for IgG)
IgM
Best agglutinin – larger complexes
IgM
() – predominant type of IgA
IgA1
Additional Ig for newborns and infants
IgA
Breastfeeding mother can transfer (?) thru breastmilk to the baby (placenta for IgG)
IgA
Unknown function at first
IgD
control of immune response between lymphocyte and macrophages; has something to do with maturation of T cells
IgD
has surface markers of IgM and IgD
mature T cell
did not encountered and Ag
unstimulated cell
can interact w/ an Ag
immunocompetent B cell
To maintain homeostasis or balance
Excess = autoimmune disorder (attacking of own cells, hyperactive, oversensitive)
Postulated as anti-idiotypic antibody involved in a feedback mechanism to switch off B-CELLS
2nd to greatest conc in serum
IgD
easily destroyed by heat
Heat-labile
mast cells and basophils granules
histamine and heparin
Eosinophil granules
Major Basic protein and Eosinophil Cationic Protein