Immunoglobulins (Igs) or antibodies are proteins produced by plasma cells that recognize and bind to specific antigens. There are five classes of Igs (IgG, IgA, IgM, IgD, IgE) which have different structures and properties. IgG is the most abundant Ig and provides long-term immunity. IgM is the first antibody produced during initial infection and activates the complement system. IgA is found in secretions and provides immunity at mucosal surfaces. B cells produce antibodies through clonal selection in response to antigens. Antibody binding leads to processes like neutralization, opsonization, and complement activation that help clear pathogens.

1. IMMUNOGLOBULINS AND THEIR
FUNCTIONS
PRESENTED BY :
roshni maurya

2. WHAT ARE ANTIBODIES? (Ab)
 Proteins that recognize and bind to a particular
antigen with very high specificity.
 Made in response to exposure to the antigen.
 One virus or microbe may have several antigenic
determinant sites, to which different antibodies may
bind.
 Each antibody has at least two identical sites that
bind antigen: Antigen binding sites.
 Valence of an antibody: Number of antigen binding
sites. Most are bivalent.
 Belong to a group of serum proteins called
immunoglobulins (Igs).

3. WHAT ARE IMMUNOGLOBULINS?(Ig)
 In 1964,endorsed by WHO, the generic term ‘
immunoglobulin’ was internationally accepted for ‘
proteins of animal origin endowed with known
antibody activity and for certain proteins related to
them by chemical structure.’
 Ig are synthesized by plasma cells, to some extent
by lymphocyte.
 Ig provide a structural and chemical concept, while
the term ‘antibody’ is a biological and functional
concept.
 All Ab are igs, but all igs may not be antibodies.

5. WHAT IS THE IMMUNOGLOBULIN
SUPERFAMILY
 Proteins with structural feature first defined in
immunoglobulins
 Characteristic structural feature
◦ Sequence of Domains providing stable conformation
 Domain
◦ Polypeptide (100 to 110 amino acids) chain folded
into sandwich (2 slices of bread) held together by
disulfide bond
 IG superfamily members
◦ Antibodies, B cell receptors, T cell receptors, MHC
molecules and others

6. STRUCTURE OF ANTIBODIES
 Antibodies are glycoproteins composed of
◦ Polypeptide chains and carbohydrate
 Monomeric structure
◦ Polypeptide chains
 2 identical heavy chains
 2 identical light chains
◦ Polypeptide chains joined by disulfide bonds
◦ Carbohydrate

7. STRUCTURE OF ANTIBODIES
 Polypeptide chains have variable and
constant regions
◦ Variable
 N (amino)-terminal of polypeptide chain
 Antigen binding site
◦ Constant
 C (carboxyl)-terminal of polypeptide chain
 Binding sites for cell surface receptors and complement
 Structure represented by the letter “Y”
 Y shaped molecule cleaved by protease
papain
◦ Fragment antigen binding (Fab)
◦ Fragment crystallizable (Fc)

10. H chains are distinct for each of the five Ig
classes or isotypes and are designated γ α μ δ
ε for the respective classes of Ig, namely IgG,
IgA ,IgM ,
IgD IgE.
L chains are one of two types designated κ and
λ and only one type is found in Ig.
Human Immunoglobulin
Light Chain Types
Kappa
Lambda

11. L and H chains are subdivided into
variable and constant regions. The regions
are composed of three-dimensionally folded,
repeating segments called domains. An L
chain consists of one variable (VL) and one
constant (CL) domain. Most H chains
c o n s i s t
of one variable (VH) and three constant(CH)
domains.(IgG and IgA have three CH
domains,whereas IgM and IgE have four.)

12. The variable regions are
responsible for antigenbinding,whereas the
constant regions are responsible for
various biologic functions eg, complement
activation and binding to cell surface
receptors.
The variable regions of L have three
extremely variable (“hypervariable / hot
spots”) amino acid sequence at the
amino-terminal end that form the antigen-
binding site .H chain have 4 such region.

13. Immunoglobulin Fragments:
Structure/Function Relationships
Ag
Binding
Complement Binding Site
Placental
Transfer
Binding to Fc
Receptors

14. Structure of the Variable Region
 Hypervariable (HVR) or complementarity
determining regions (CDR)
FR1 FR2 FR3 FR4
HVR1
HVR2
HVR3
VariabilityIndex
25 7
5
50 10
0Amino acid
residue
15
0
10
0
5
0
0
Framework regions

15. A. Immunoglobulin classes - The immunoglobulins can be divided
into 5 different classes based on differences in the amino acid
sequences in the constant region of the heavy chains. All
immunoglobulins within a given class will have very similar heavy chain
constant regions. These differences can be detected by sequence
studies or more commonly by serological means (i.e. by the use of
antibodies directed to these differences).
1. IgG - Gamma heavy chains
2. IgM - Mu heavy chains
3. IgA - Alpha heavy chains
4. IgD - Delta heavy chains
5. IgE - Epsilon heavy chains

16. . 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. All
immunoglobulins within a subclass will have very similar heavy chain
constant region amino acid sequences. Again these differences are
most commonly detected by serological means.
1. IgG Subclasses
a) IgG1 - Gamma 1 heavy chains
b) IgG2 - Gamma 2 heavy chains
c) IgG3 - Gamma 3 heavy chains
d) IgG4 - Gamma 4 heavy chains
2. IgA Subclasses
a) IgA1 - Alpha 1 heavy chains
b) IgA2 - Alpha 2 heavy chains

17. CLASSES, SUBCLASSES AND
PHYSICAL PROPERTIES OF
IMMUNOGLOBULINS
Subclasses are numbered according to plasma
concentration
Classes Subclasses
IgG IgG1, IgG2, IgG3, IgG4
IgA IgA1, IgA2
IgM
IgD
IgE

18. C. Immunoglobulin Types - Immunoglobulins can also be classified by the type of
light chain that they have. Light chain types are based on differences in the amino
acid sequence in the constant region of the light chain. These differences are
detected by serological means.
1. Kappa light chains
2. Lambda light chains
D. 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.
1. Lambda subtypes
a) Lambda 1
b) Lambda 2
c) Lambda 3
d) Lambda 4
E. Nomenclature - Immunoglobulins are named based on the class, or subclass of
the heavy chain and type or subtype of light chain. Unless it is stated precisely you
are to assume that all subclass, types and subtypes are present. IgG means that
all subclasses and types are present.
F. Heterogeneity - Immunoglobulins considered as a population of molecules are
normally very heterogeneous because they are composed of different classes and
subclasses each of which has different types and subtypes of light chains. In
addition, different immunoglobulin molecules can have different antigen binding
properties because of different VH and VL regions.

19. FUNCTIONS AND
PROPERTIES OF ANTIBODY
 Neutralization
◦ Direct inactivation of pathogen or toxin thereby
preventing its interaction with human cells
 Opsonization
◦ Coating of pathogens for more efficient
phagocytosis
 Activation of complement
◦ More efficient phagocytosis
◦ Direct killing

21. IgG
 Structure
◦ Monomer (7S)
IgG1, IgG2 and
IgG4
IgG3

22. IgG
 Properties
◦ Major serum Ig
◦ Major Ig in extravascular spaces
◦ The only antibody to cross the placenta
◦ Fixes complement
◦ Binds to Fc receptors
 Phagocytes - opsonization
 NK cells – ADCC

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BIOLOGICAL & CHEMICAL PROPERTIES OF Igs
 IgG. Is the major immunoglobulin in human serum,
accounting for approximately 80%. Concentration of
approximately 12 mg/ml
 IgG is a monomer consisting of identical pairs of H and L
chains linked by disulfide bridges.
 Four subclasses of IgG have been identified, based on H chain
differences: IgG1, IgG2, IgG3, and IgG4.
 IgG is the only immunoglobulin that can cross the placenta in
humans and protect the infant during the first months of life.
 IgG molecules are capable of binding complement by the
classical pathway (except for the IgG4, which activate by the
alternative pathway).

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BIOLOGICAL AND CHEMICAL PROPERTIES
OF IMMUNOGLOBULINS
 IgG is the major antibody produced in the
secondary immune response
 IgG has a half-life of approximately 23 days
 Effective antitoxic immunity is exclusively IgG.
 IgG is the major opsonizing immunoglobulin in
phagocytosis; neutrophils have receptors for the Fc
fragments of IgGI and IgG3.
 IgG appears late but persists for longer period. It
appears after initial response which is IgM in
nature.

25. IgM
 Structure
◦ Pentamer
(19S)
composed
5 H2L2 units
plus one
molecule of
J chain
◦ Extra domain
(CH4)
◦ J chain
C4
J Chain

26. IgM
 Properties
◦ 3rd highest serum Ig
◦ First Ig made by fetus
and B cells
◦ Produced early in the
primary response
◦ The most efficient Ig
◦ Fixes complement
Tail
Piec
e
Agglutinating Ig
Binds to Fc receptors
B cell surface Ig

27. IgM ANTIBODY OF THE
IMMUNE RESPONSE
 First isotype produced in primary response
◦ May or may not be produced in secondary response
◦ Produced before B cells undergo somatic
hypermutation
 Occurs as pentamer with J chain
◦ Found primarily in blood and lymph
 Multiple binding sites confers high avidity and
compensates for low affinity of monomers
 Highly effective in complement activation
 Functions as rheumatoid factor.
 Represents about 8% to 10% of the total serum Igs .
Concentration of ≈ I.2 mg/ml., half life is 5 days

28. Fixation of C1 by IgG and IgM
Abs
No activation Activation

29. IgA
◦ Structure
 Serum – monomer
 Secretions (sIgA)
 Dimer (11S), sIgA molecule consists of two H2L2 units
plus one molecule each of J chain and secretory
component(SC or SP)
J
Chain
Secretory
Piece

30. IgA ANTIBODY OF THE
IMMUNE RESPONSE
 Two subclasses (IgA1 and IgA2) and two
forms (monomeric and dimeric)
 Monomeric
◦ Located in blood and extracellular spaces
◦ Predominately IgA1
 Ratio of IgA1 to IgA2 is 10:1
◦ Functions as rheumatoid factor
 Dimeric
◦ Located in mucous membranes and secretions
◦ Predominately IgA2
◦ Ratio of IgA2 to IgA1 is 3:2
◦ J chain like IgM

31. •Origin of sIgA: The SP is a polypeptide synthesized
by epithelial cells that provides for IgA passage to the
mucosal surface. It also protests IgA from being
degraded in the intestinal tract.

32. IgA
 Properties
◦ 2nd highest serum Ig
◦ Major secretory Ig ( saliva, tears,
respiratory, intestinal, and genital
tract secretions.)
◦ Does not fix complement unless
aggregated
◦ Binds to Fc receptors on some cells

33. IgD
 Structure
◦ Monomer
◦ Tail piece
Tail
Piece

34. IgD
Properties
◦ 4th highest serum Ig
◦ B cell surface Ig
◦ Does not bind complement

35. IgE
 Structure
Monomer
Extra domain (CH4)
C4

36. IgE
 Structure
 Properties
◦ Least common serum Ig
◦ Allergic reactions
◦ Parasitic infections
◦ Does not fix complement

37. IgG IgA IgM IgD IgE
Sedimentation coefficient
(S)
7 7 19 7 8
Molecular weight 150,000 160,000 900,000 180,000 190,000
Serum
concentration(mg/l)
12 2 1.2 0.03 0.00004
Half life (days) 23 6 5 2-8 1-5
Daily production (mg/kg) 34 24 3.3 0.4 0.0023
Intravascular
distribution(%)
45 42 80 75 50
Carbohydrate (%) 3 8 12 13 12
Complement fixation
Classical ++ - +++ - -
Alternative - + - - -
Placental transport + - - - -
Present in milk + + - - -
Selective secretion by - + - - -

38. ABNORMAL
IMMUNOGLOBULINS The earliest description of an abnormal immunoglobulins was
the discovery Bence Jones (1847) of the protein that bears
his name . Bence Jones protein is found typically in multiple
myeloma.
 It can be identified in urine by its characteristics property of
coagulation when heated to 50°C but redissolving at 70°C.
Bence Jones are light chain immunoglobulins and so may
occur as kappa or lambda forms.
 Multiple myeloma may affect plasma synthesising IgG , IgA,
IgD or IgE. Similarly involvement of IgM producing cells is
known as Waldenstrom’s macrolobulinemia. In this condition
, there occurs excessive production of the respective
myeloma protein (M protein) and of their chains (Bence
Jones protein).
 Cryoglobulinemia is a condition in which there is the
formation of a gel or a precipitate on cooling the serum,

39. How Do B Cells Produce Antibodies?
◦ B cells develop from stem cells in the bone
marrow of adults (liver of fetuses).
◦ After maturation B cells migrate to lymphoid
organs (lymph node or spleen).
◦ Clonal Selection: When a B cell encounters
an antigen it recognizes, it is stimulated and
divides into many clones called plasma cells,
which actively secrete antibodies.
◦ Each B cell produces antibodies that will
recognize only one antigenic determinant.

40. Clonal Selection of B Cells is Caused
by Antigenic Stimulation

41. Consequences of Antigen-Antibody
Binding
Antigen-Antibody Complex: Formed when an
antibody binds to an antigen it recognizes.
Affinity: A measure of binding strength.
1. Agglutination: Antibodies cause antigens
(microbes) to clump together.
 IgM (decavalent) is more effective that IgG
(bivalent).
 Hemagglutination: Agglutination of red blood
cells. Used to determine ABO blood types and to
detect influenza and measles viruses.
2. Opsonization: Antigen (microbe) is covered
with antibodies that enhances its ingestion
and lysis by phagocytic cells.

42. Consequences of Antibody Binding

43. Humoral Immunity (Continued)
3. Neutralization: IgG inactivates viruses by
binding to their surface and neutralize toxins
by blocking their active sites.
4. Antibody-dependent cell-mediated
cytotoxicity: Used to destroy large
organisms (e.g.: worms). Target organism is
coated with antibodies and bombarded with
chemicals from nonspecific immune cells.
5. Complement Activation: Both IgG and IgM
trigger the complement system which results
in cell lysis and inflammation.

44. Consequences of Antibody Binding

45. Immunological Memory
Antibody Titer: The amount of antibody in the
serum.
Pattern of Antibody Levels During Infection
Primary Response:
◦ After initial exposure to antigen, no
antibodies are found in serum for several
days.
◦ A gradual increase in titer, first of IgM and
then of IgG is observed.
◦ Most B cells become plasma cells, but some
B cells become long living memory cells.
◦ Gradual decline of antibodies follows.

46. Immunological Memory (Continued)
Secondary Response:
◦ Subsequent exposure to the same antigen
displays a faster and more intense antibody
response.
◦ Increased antibody response is due to the
existence of memory cells, which rapidly
produce plasma cells upon antigen
stimulation.

47. Antibody Response After Exposure to
Antigen

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Allo-antibodies & Auto-antibodies
 Antigens that initiate the immune cascades
results in the formation of either allo-abs or
auto-abs.
 Allo-antibodies are produced after exposure
to genetically different or non-self, antigens
of the same species.
 Auto-antibodies are produced in response
to self antigens.

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Laboratory Examination of Reaction
between Ags and Abs
 In vitro testing for the detection of Ags or Abs may be
accomplished by a variety of immunologic techniques.
Such techniques as agglutination, precipitation,
agglutination inhibition, and hemolysis are the most
commonly used methods to detect the presence of blood
group Ags or Abs.
 In blood bank testing, agglutination reactions are the
major manifestation of the blood group Ag-Ab response.
Typing for ABO, Rh, and other blood group Ags is
accomplished by agglutination reaction.

50. drmsaiem
Laboratory Examination of Reaction between
Ags and Abs
 There are two stages for agglutination to develop;
 Stage 1: known as sensitization, Ab binding occurs.
Antigenic determinants on the red cell membrane combine
with the antigen combining site (Fab region) on the
variable regions of the immunoglobulin heavy and light
chains.
 Stage 2: a lattice structure composed of multiple Ag-Ab
bridges between Abs and red cell Ags is formed visible
agglutination is present during this stage.

51. CONCLUSION
 In general ,IgG protects the body
fluids, IgA protects body surfaces
and IgM the blood stream, while
IgE mediates reaginic
hypersensitivity. IgD is a
recognition molecule on the
surface of B lymphocytes.

52. thank u!