Immunoglobulins types

about immunoglobulins

1. Immunoglobulins

2. What are Immunoglobulins?
Glycoprotein moleculesthat are produced by plasma cells in
response to an immunogen and which function as antibodies,
present in the serumand tissue fluidsof all mammals.
Immunoglobulins are the critical ingredients of humoral acquired
immune response.
Basic structure of Ig:
Immunoglobulins –heterogeneous
Myeloma proteins -homogeneous immunoglobulins

3. Two Forms of Immunoglobulin
Membrane-bound receptor Soluble antibody
Igαand Igβinvolve in transducing signals as cytoplasmic tail of Ig is short in BCR

4. General Functions of Immunoglobulins
1.Antigen binding:
Ag binding by Ab is the primary functionof Ab and can result in
protection of the host.
Ig bind specifically to one or a few closely related antigens.
Each Ig actually binds to a specific Ag determinant.
Valency-refers to the number of antigenic determinants that
an individual Ab molecule can bind. The valency of all Ab is at
least two and in some instances more.

5. 2. Effector Functions (Secondary)
•to carry out a particular effector function requires that the Ab bind to
its Ag. Not every Ig will mediate all effector functions.
–1. Fixation of complement-lysis of cells, release of biologically
active molecules
–2. Binding to various cell types-phagocytic cells, lymphocytes,
platelets, mast cells, and basophils have receptors that bind Ig
and the binding can activate the cells to perform some function.
–Neutalization
–Opsonization
–Antibody-dependent cell-mediated cytotoxicity,ADCC
–Mediate hypersensitivity type I
–Some Ig also bind to receptors on placental trophoblasts and
transfer Ig across the placentaand the transferred maternal Ab
provide immunity to the fetus and newborn.

6. Immunoglobulin Structure
•Variable(V) &
Constant (C)
Regions
–V
L& C
L
–V
H& C
H
•Hinge Region
C
H1
V
L
C
L
V
H
C
H2 C
H3
Hinge Region
Carbohydrate
Disulfide bond

7. •Immunoglobulins are composed of four polypeptide chains: two "light" chains (lambda or kappa),
and two "heavy" chains (alpha, delta, gamma, epsilon or mu).
•The type of heavy chain determines the immunoglobulin isotype (IgA, IgD, IgG, IgE, IgM,
respectively).
•Light chains are composed of 220 amino acid residues while heavy chains are composed of 440-
550 amino acids.
•Each chain has "constant" and "variable" regions.
•Variable regions are contained within the amino (NH2) terminal end of the polypeptide chain
(amino acids 1-110).
•
•When comparing one antibody to another, these amino acid sequences are quite distinct.
Constant regions, comprising amino acids 111-220 (or 440-550), are rather uniform, in
comparison, from one antibody to another, within the same isotype.
•"Hypervariable" regions, or "Complementarity Determining Regions" (CDRs) are found within the
variable regions of both the heavy and light chains.
•These regions serve to recognize and bind specifically to antigen. The four polypeptide chains are
held together by covalent disulfide (-S-S-) bonds.

9. Structure of Ig
A. Heavy and Light Chains –
–All Ig have a four chain structure as their basic unit. They are composed of two identical
light chains (23Kd) and two identical heavy chains (50-70Kd)
B. Disulfide bonds
1. Inter-chain -The heavy and light chains and the two heavy chains are held
together by disulfide bonds and by non-covalent interactions. The number of interchain
disulfide bonds varies among different immunoglobulin molecules.
2. Intra-chain -Within each of the polypeptide chains there are intra-chain
disulfide bonds.
C. Variable (V) and Constant (C) Regions-heavy and light chain could be divided into
two regions based on variability in the amino acid sequences.
–1. Light Chain -VL (110 aa) and CL (110 aa)
–2. Heavy Chain -VH (110 aa) and CH (330-440 aa)

10. Hinge Region-The region at which the arms of the antibody molecule forms a Y is
called the hinge region because there is some flexibility in the molecule at this point.
-Rich in proline residues (flexible)
–Hinge found in IgG, IgA and IgD
–Proline residuesare target for proteolytic digestion (papain and pepsin)
–Rich in cysteine residues (disulfide bonds)
–IgM and IgE lackhinge region, they instead have extra C
H4 Domain
E. Domains -it is folded into globular regions each of which contains an intra-chain
disulfide bond. These regions are called domains.
–1. Light Chain Domains -VL and CL
–2. Heavy Chain Domains -VH, CH1 -CH3 (or CH4)
F. Oligosaccharides -Carbohydrates are attached to the CH2 domain in most Ig.
However, in some cases carbohydrates may also be attached at other locations.

11. Functions of the domains on Ig
VH, VL —antigen binding sites
CH1-3, CL —genetic markers of Ig
CH2(IgG), CH3(IgM) —C1q binding sites
CH2-CH3(IgG) —binding to placenta
CH3(IgG) —FcγR binding site
CH4(IgE) —FcεR binding site.

12. STRUCTURE OF THE VARIABLE REGION
A. Hypervariable (HVR) or complementarity determining regions (CDR)
–Comparisons of the amino acid sequences of the variable regions of Ig's
show that most of the variability resides in three regions called the
hypervariable regions or the complementarity determining regions.
–Antibodies with different specificities (i.e. different combining sites)
have different CDR's while antibodies of the exact same specificity have
identical CDR's (i.e. CDR --> Ab Combing site).
–CDR's are found in both the H and the L chains.
B. Framework regions
–The regions between the CDR's in the variable region are called the
framework regions (FR)

13. •Hypervariable
region (HVR) also
called
Complementarity
Determining
Regions (CDRs),

14. Proteolytic digestion of Ig
•Ig digestion with papain:
–Fab –(Fragment Ag binding site)
Digestion with papain breaks the Ig
molecule in the hinge region before
the inter-chain disulfide bond. This
results in the formation of two
identical fragments (Fab) that contain
the light chain and the VH and CH1
domains of the heavy chain.
–They contain the antigen binding
sites of the antibody.
–Each Fab fragment is monovalent
whereas the original molecule was
divalent.
–Fc –(Fragment crystaallization) a
fragment that contains the remaining
two heavy chains each containing a
CH2 and CH3 domain.

15. Ig cleavage with pepsin
C. F(ab')2 -Treatment of Ig
with pepsin results in
cleavage of the heavy
chain after the H-H inter-
chain disulfide bonds
resulting in a fragment that
contains both antigen
binding sites.
This fragment is called
F(ab')2 because it was
divalent.
The Fc region of the molecule
is digested into small
peptides by pepsin.

17. HUMAN IMMUNOGLOBULIN CLASSES, SUBCLASSES,
TYPES AND SUBTYPES
5 different classes based on differences in the amino acid sequences in the constant
region of the heavy chains.
•IgG -Gamma (γ) heavy chains
•IgM -Mu (μ) heavy chains
•IgA -Alpha (α) heavy chains
•IgD -Delta (δ) heavy chains
•IgE -Epsilon (ε) heavy chains
Immunoglobulin Subclasses -The classes of immunoglobulins can de divided into
subclasses based on small differences in the amino acid sequences in the constant
region of the heavy chains.
•1. IgG Subclasses
–a) IgG1 -Gamma 1 (γ1) heavy chains
–b) IgG2 -Gamma 2 (γ2) heavy chains
–c) IgG3 -Gamma 3 (γ3) heavy chains
–d) IgG4 -Gamma 4 (γ4) heavy chains
•2. IgA Subclasses
–a) IgA1 -Alpha 1 (α1) heavy chains
–b) IgA2 -Alpha 2 (α2) heavy chains

18. Five Classes of Immunoglobulin

19. Immunoglobulin Types -Ig can also be classified by the type of light
chainthat they have. Light chain types are based on differences in
the amino acid sequence in the constant region of the light chain.
–1. Kappa light chains (κ)
–2. Lambda light chains (λ)
Immunoglobulin Subtypes -The light chains can also be divided into
subtypes based on differences in the amino acid sequences in the
constant region of the light chain.
Lambda subtypes
–a) Lambda 1 (λ1)
–b) Lambda 2 (λ2)
–c) Lambda 3 (λ3)
–d) Lambda 4 (λ4)

20. IgG
Structure –
All IgG's are monomers (7S immunoglobulin).
The subclasses differ in the number of disulfide bonds and length of the hinge region.
Properties –
Most versatile immunoglobulin because it is capable of carrying out all of the functions of
immunoglobulin molecules.
–a) IgG is the major Ig in serum-75% of serum Ig is IgG (~10mg/mL)
–b) IgG is the major Ig in extra vascular spaces
–c) IgG is the only class of Ig that crosses the placenta. Not all subclasses cross equally; IgG2
does not cross well.
–d) Fixes complement-Not all subclasses fix equally well; IgG4 does not fix complement
–e) Binding to cells-Macrophages, monocytes, PMNs and some lymphocytes have Fc
receptors for the Fc region of IgG.
•Not all subclasses bind equally well; IgG2 and IgG4 do not bind to Fc receptors.
Site of action: Blood, Tissue fluid, can cross placenta
Valence: 2
Function: Increase macrophage activity, Antitoxins, Agglutination

22. IgM
Structure –
IgM exists as a pentamer (19S immunoglobulin) but it can also exist as a monomer.
IgM has an extra domain on the μ chain (CH4)and it has another proteincovalently bound via a S-S
bond called the J chain. This chain functions in polymerization of the molecule into a pentamer.
Properties
–a) IgM is the 3rd most common serum Ig (5-10 % of serum Ig and ranges 1.5mg/mL)
–First Ig of primary immune response and has high valence
–b) IgM is the first Ig to be made by the fetusand the first Ig to be made by a virgin B cellswhen
it is stimulated by antigen.
–c) IgM is a good complement fixing Ig.
–d) IgM is also a good agglutinating Ig .Thus, IgM antibodies are very good in clumping
microorganisms for eventual elimination from the body.
–e) IgM binds to some cellsvia Fc receptors.
–f) B cell surface Ig-Surface IgM exists as a monomer and lacks J chainbut it has an extra 20
amino acids at the C-terminal end to anchor it into the membrane. Cell surface IgM functions as
a receptor for antigen on B cells.
•Surface IgM is noncovalently associated with two additional proteins in the membrane of
the B cell called Ig-α and Ig-β. These additional proteins act as signal transducing
molecules since the cytoplasmic tail of the Ig molecule itself is too short to transduce a
signal.
Site of action: Blood, Tissue fluid
Valence: 10
Function: Agglutination

23. IgM

24. IgA
1.Structure
-Serum IgA is a monomer but IgA found in secretions is a dimer
-10-15% of serum Ig
-When IgA exists as a dimer, a J chain is associated with it.
-IgA is sometimes referred to as 11S immunoglobulin.
-Unlike the remainder of the IgA which is made in the plasma cell, the secretory piece is
made in epithelial cells.
-The secretory piece helps IgA to be transported across mucosa and also protects it
from degradation in the secretions.
2. Properties
a) IgA is the2nd most common serum Ig.
b) IgA is themajor class of Ig in secretions -tears, saliva, colostrum, mucus. It is
important in local (mucosal) immunity.
c) Normally IgA does not fix complement, unless aggregated.
d) IgA can binding to some cells-PMNs and some lymphocytes.
Valence: 2 or 4, Functions: Stop bacteria adhering to host cells, Prevents bacteria forming
colonies on mucous membranes

25. IgA Antibody Transport Across Cell
(Transcytosis)
Transcytosisis the
process by which various
macromolecules are
transported across the
interior of a cell.
Macromolecules are
captured in vesicles on
one side of the cell, drawn
across the cell, and
ejected on the other side.

26. IgA
J ChainSecretory Piece

27. IgD
1.Structure -IgD exists only as a monomer.
2. Properties
•a) IgD is found in low levels in serum; its role in serum
uncertain.
•b) IgD is primarily found on B cell surfaceswhere it
functions as a receptor for antigen. IgD on the surface of B
cells has extra amino acids at C-terminal end for anchoring
to the membrane. It also associates with the Ig-α and Ig-β
chains.
•c) IgD does not bind complement.

28. IgD

29. IgE
•Structure -IgE exists as a monomer and has an extra domain in the
constant region.
•Properties
–a) IgE is the least common serum Igsince it binds very tightly to Fc
receptors on basophils and mast cells. Does not require Ag binding.
–b) Involved in allergic reactions–binding to basophils and mast cells,
IgE is involved in allergic reactions.
–c) IgE also plays a role in parasitic helminth diseases. Since serum IgE
levels rise in parasitic diseases, measuring IgE levels is helpful in
diagnosing parasitic infections.
–Eosinophils have Fc receptors for IgEand binding of eosinophils to IgE-
coated helminths results in killing of the parasite.
–d) IgE does not fix complement.
•Site of action: Tissue, Valence: 2,
•Functions: Activate mast cells HISTAMINE, Worm response

30. IgE

31. Isotypes, Allotypes, and Idiotypes
of Immunoglobulins

32. Isotype
An isotype is determined by the primary sequence of amino acids in
the constant region of the heavy chain.
All the heavy chainconstant region structures which give rise to
classesand subclassesare expressed together in the serum of a
normal subject are called Isotypic variants.
Each of those is called Isotype.
The type of heavy chain an immunoglobulin possesses determines the
immunoglobulin "isotype".
Eg. IgA, IgD, IgG, IgE and IgM

33. Allotypes
Amino acid sequences of immunoglobulins differ from each other in
a same species, and this is called inherited sequence variation.
The variations in heavy chain genesare called Allotypes.
Like isotypes, allotypes are determined by the amino acid sequence
and corresponding three-dimensional structure of the constant
region of the immunoglobulin molecule.
Unlike isotypes, allotypes reflect genetic differences between
members of the same species.This means that not all members of
the species will possess any particular allotype.

34. Idiotypes
The variations of amino acid sequences within the variation
domainson light and heavy chains are called Idiotypes.
Unlike isotypes and allotypes, idiotypes are determined by the
amino acid sequence and corresponding three-dimensional
structure of the variable region of the immunoglobulin molecule.
In this regard, idiotypes reflect the antigen binding specificity of any
particular antibody molecule.
Idiotypes are so unique that an individual person is probably
capable of generating antibodies directed against their own
idiotypic determinants.