Immunoglobulins, also known as antibodies, are glycoprotein molecules produced by B cells and plasma cells. They function to bind pathogens tightly and target the immune system's destructive components against extracellular pathogens. Antibodies have a Y-shaped structure consisting of two heavy chains and two light chains that give them regions for antigen binding and effector functions. The five major classes of antibodies - IgG, IgM, IgA, IgD, and IgE - have distinct structures, concentrations, and roles in the immune response. Antibodies provide protection through neutralization, opsonization, complement activation, and more.

1. IMMUNOGLOBULINS
STRUCTURE AND FUNCTION

2. IMMUNOGLOBULINS
Definition
Glycoprotein molecules that
are present on B cells (BCR) or
produced by plasma cells
(usually referred to as
antibodies) in response to an
immunogen

3.  Antibodies production is the sole function
of the B cells
 Not toxic or destructive, bind the
pathogen tightly and target destructive
components of the immune system
 Antibodies are useful in the defense
against extracellular pathogens
 Antibodies are secreted in the secondary
lymphoid organs and in bone marrow and
find their way to the extracellular spaces
 During the course of an infection
antibody effectiveness improves steadily

4. PHASES OF B CELL RESPONSE !

5. IMMUNOGLOBULIN STRUCTURE
• 2x Heavy chain (light blue)
• 2x light chain (dark blue)
• Variable regions  antigen binding
• Constant regions
hinge region
carbohydrate
disulfide bond
CH
1
VL
CL
VH
CH2 CH3
!

6. Ribbon structure of IgG

7. Antibody
BCR (B cell receptor)
!!
MEMBRANE BOUND!
Associated chains
for signaling
Transmembrane
domain
Cytoplasmic
domain
Antigen recognition and B cell
activation
SOLUBLE (freely circulating)
Antigen recognition and effector
functions.
Produced by plasma cells

8. s
s
s
s
s
s
s
s
s s
s s
CH2
CH3
s
s
s
s
s
s
s
s
s
s
VL
VH
CL
CH1
s
s
s
s
s
s
s
s
s
s
effektor funkciók
konstans domének
antigénkötés
variábilis dom ének
ANTIBODY DOMAINS AND THEIR FUNCTIONS
!
!
Constant domain
Effector functions
Antigen recognition
Variable domain

9. mIg = BCR
Associated chains providing
signaling capacity
!

10. B cell
B CELL ACTIVATION
BCR oligomerization results in B cell
activation, proliferation and differentiation
!

11. FLEXIBILITY OF ANTIBODIES

12. FEATURES OF ANTIBODY-ANTIGEN INTERACTION
Valency: numbers of antigen
epitopes an antibody binds
Affinity: the strength of
interaction between a specific
antigen and one binding site
of the antibody
Avidity: The overall strength
of binding at multiple sites in
an antibody

13. ANTIGEN BINDING
Antigen Binding
Fragment (Fab)
Complement binding site
Placental transfer
Constant fragment (Fc)
Binding to Fc receptors
on phagocytic cells

14. Sequence variability of H/L-
chain constant regions
VARIABILITY IN DIFFERENT REGIONS OF THE Ig
DETERMINES Ig SPECIFICITY OR CLASS
isotype
Sequence variability of H/L-
chain variable regions
Idiotype

15. DIFFERENT VARIABLE REGIONS 
DIFFERENT ANTIGEN-BINDING SITES 
DIFFERENT SPECIFICITIES

16. ANTIGEN BINDING FRAGMENT (Fab)
CONTAINS HYPERVARIABLE REGIONS
DNA recombination of gene
segments encoding these
regions (variable heavy and
light polypeptide chains) gives
a huge number of variability
during B cell development in
the bone marrow.
Aka. Somatic recombination

17. COMPLEMENTARY DETERMINING REGIONS (CDR)
Epitope
CDR1
CDR2
CDR3
CDR1
CDR2
CDR3
Light
chain
Heavy
chain

18. Sequence variability of H/L-
chain constant regions
VARIABILITY IN DIFFERENT REGIONS OF THE Ig
DETERMINES Ig SPECIFICITY OR CLASS
Sequence variability of H/L-
chain constant regions
Isotype

19. • 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
HUMAN IMMUNOGLOBULIN CLASSES
ENCODED BY DIFFERENT STRUCTURAL GENE SEGMENTS (ISOTYPES)
• kappa (κ)
• lambda (λ)
Heavy chain types:
Light chain types:
!

20. ISOTYPE SWITCHING

21. PHASES OF B CELL RESPONSE !

22. Ig isotype Serum
concentration
Characteristics, functions
12-14 mg/ml
 Major isotype of secondary
(memory) immune response
 Complexed with antigen activates
effector functions (Fc-receptor
binding, complement activation
Trace
amounts
 The first isotype in B-lymphocyte
membrane
 Function in serum is not known
Trace
amounts
 Major isotype in protection against
parasites
 Mediator of allergic reactions (binds
to basophils and mast cells)
3-3,5 mg/ml
 Major isotype of secretions (saliva,
tear, milk)
 Protection of mucosal surfaces
1-2 mg/ml
 Major isotype of primary immune
responses
 Complexed with antigen activates
complement
 Agglutinates microbes
 The monomeric form is expressed in
B-lymphocyte membrane as antigen
binding receptor
MAIN CHARACTERISTICS OF ANTIBODY ISOTYPES

23. MAIN CHARACTERISTICS OF ANTIBODY ISOTYPES

24. Ig. Concentration
napok
primer response
„A
” antig n
é
IgM
IgG
IgA
IgE
Szekunder ’lasyecondary respo
„A
” és
antigén
„B
”
5 10 15 20 25 30
IgM
secondary response against
antigen A
Primary response
against antigen A
Level of antibodies
napok
primary response
against antigen B
Antigen A
Days
Antigen A and B
ANTIBODY PRODUCTION DURING THE
PRIMARY AND THE SECONDARY IMMUNE RESPONSES

25. ANTIBODY PRODUCTION DURING THE
PRIMARY AND THE SECONDARY IMMUNE RESPONSE !

26. EFFECTOR FUNCTIONS OF ANTIBODIES
Antibody-mediated immune responses
• NEUTRALIZATION
• OPSONIZATION
ADCC
MAST CELL DEGRANULATION
• COMPLEMENT FIXATION
!
!

27. NEUTRALIZATION
Covering of the pathogen’s surface
prevents replication and growth

28. Antigen binding
Complement binding site
Placental transfer
Binding to Fc receptors

29. OPSONIZATION
Flagging a pathogen
Antigen binding portion (Fab)
binds the pathogen, the Fc
region binds phagocytic cells
Fc-receptors speeding up the
process of phagocytosis

30. Antibody Dependent Cellular Cytotoxicity
(ADCC)

31. (A) High-affinity FcRs on the surface of the cell bind monomeric
Ig before it binds to antigen. (mast cell)
(B) Low-affinity FcRs bind multiple Igs that have already bound to
a multivalent antigen. (macrophage, NK cell)
MAST CELL DEGRANULATION
FcεRI
+
IgEs

32. Antigen binding
Complement binding site
Placental transfer
Binding to Fc receptors

33. COMPLEMENT FIXATION
IgM and IgGs activate the classical pathway of
the complement system

34. Bacterium
Complement receptor
Macrophage
OPSONIZATION BY C3b
C3b

35. IMMUNOGLOBULIN ISOTYPES HAVE EACH
THEIR SPECIFIC CAPABILITIES

36. Antigen binding
Complement binding site
Placental transfer
Binding to Fc receptors
FcRn on the placenta
facilitate the transfer of
maternal IgG to the fetus’s
circulation

37. IgG
IgM
IgA
AFTER BIRTH
breast milk
IgA
0
100%
( adult)
3 3
year
2 5
4
6 adult
9 1
month
maternal IgG
BEFORE BIRTH
PRODUCTION OF IMMUNOGLOBULINS
 IgG transport is so efficient that at birth babies have as high a level of IgG in
their plasma as their mothers
 These transfers are a form of passive immunization. The babies protection by
IgG and IgA is against those pathogen that the mother has mounted
 At the first year (esp.3-12m) maternal IgGs are catabolized and breast feeding
diminishes so babies become most susceptible/vulnerable to infections

38. Pathological consequences of placental
transport of IgG
(hemolytic disease of the newborn)
Passive anti-D IgG
anti-Rh
IgM

39. DIMERIC IgA
IgA dimers are in the highly vulnerable mucosal epithelia lining the
GI, respiratory, urinary and genital tracts, the eyes, nose and throat
(Transcytosis)