Complement system Immunoglobulin

1. Complement system
Immunoglobulin
Dept of Urology
Govt Royapettah Hospital and Kilpauk Medical College
Chennai
Slides
before 1st
Section
Divider
complement
system
IMMUNOGLOBULIN
S
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2. Moderators:
Professors:
• Prof. Dr. G. Sivasankar, M.S., M.Ch.,
• Prof. Dr. A. Senthilvel, M.S., M.Ch.,
Asst Professors:
• Dr. J. Sivabalan, M.S., M.Ch.,
• Dr. R. Bhargavi, M.S., M.Ch.,
• Dr. S. Raju, M.S., M.Ch.,
• Dr. K. Muthurathinam, M.S., M.Ch.,
• Dr. D. Tamilselvan, M.S., M.Ch.,
• Dr. K. Senthilkumar, M.S., M.Ch.
Dept of Urology, GRH and KMC, Chennai. 2

3. The complement system plays an essential role in
host defense against infectious agents and in the
inflammatory process.
Nomenclature:
a. the first component of complement is named
C1 (etc.) other components are designated by
capital letters and names: Factor B, Properidin
b. when cleaved: fragments of complement
components are designated by small letters
(e.g. C3a and C3b)
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Dept of Urology, GRH and KMC, Chennai.

4. C3
C3a
C3b
Factor B Ba + Bb
Factor H
Factor I
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Dept of Urology, GRH and KMC, Chennai.

5. Complement System
Activation
Amplification
Biologic Function
Regulation
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Dept of Urology, GRH and KMC, Chennai.

6. Complement Pathways
3 pathways for activation:
1. classical: most specific (antibody
dependent activation, binds C1)
2. lectin binding: some specificity
(mannose binding protein, binds C4)
3. alternative: most primitive (non-
specific, auto-activation of C3)
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Dept of Urology, GRH and KMC, Chennai.

7. Activators
Classical pathway Alternate
pathway
1.Ag-Ab complex
2.Aggregated Ig
3.DNA
4.CRP
5.Trypsin
1.Bacterial
endotoxins
2.IgA, IgD
3.CobraVenom
4.Nephritic Factor
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Dept of Urology, GRH and KMC, Chennai.

8. Cascade:
Many of the components are enzymes that
become activated when cleaved into
two peptides
One peptide binds to the immune complex
and becomes a functional part of it
The other peptide diffuses away and can
become an inflammatory mediator
(binds to a receptor)
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Dept of Urology, GRH and KMC, Chennai.

9. 10
Dept of Urology, GRH and KMC, Chennai.

10. Lectin pathway:
➢ Lectin: protein that binds to carbohydrate
➢ MBL binds to mannose (on many bacterial
cells)
➢ MBL is produced by liver in acute-phase
inflammatory reactions
➢ Once MBL binds to target cell, a serine
protease (MASP) binds to it
➢ Acts like C1
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Dept of Urology, GRH and KMC, Chennai.

11. C3a
C3a increases the inflammatory response by
binding to mast cells and causing them to release
histamine
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Dept of Urology, GRH and KMC, Chennai.

12. Building the C3 convertase or C5
activation complex
 After enough C3b is cleaved, the surface
of the bacteria begins to become
saturated with it.
 C2b and C4b which make up the C3
activation complex has a slight affinity for
C3b and C3b binds to them
 When C3b binds to C2b and C4b it
forms a new complex referred to as the
C5 activation complex
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Dept of Urology, GRH and KMC, Chennai.

13. The C5 activation complex
 The C5 activation complex (C2b, C4b,
C3b) activates C5 proteins by cleaving
them into C5a and C5b
 Many C5b proteins are produced by the
C5activation complex. These C5b begin
to coat the surface of the bacteria.
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Dept of Urology, GRH and KMC, Chennai.

14. The function of C5a
 C5a disperses away from the bacteria.
◦ Binds to mast cells and increases inflammation.
◦ Most powerful chemotactic factor known for leukocytes
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Dept of Urology, GRH and KMC, Chennai.

15. Building the Membrane Attack complex
 C5b on the surface of bacteria binds to
C6
 The binding of C6 to C5b activates C6 so
that it can bind to C7
 C7 binds to C8 which in turn binds to
many C9’s
 Together these proteins form a circular
complex called the Membrane attack
complex (MAC)
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16. Membrane Attack complex
 The MAC causes Cytolysis.
◦ The circular membrane attack
complex acts as a channel in which
cytoplasm can rush out of and
water rushes in.
 The cells inner integrity is
compromised and it dies
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17. Functions of the complement system
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18. Amplification: many C3 molecules are hydrolyzed
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19. Alternative
pathway
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20. C3b
 Many C3b molecules are produced by the C3
activation complex.
 The C3b bind to and coat the surface of the
bacteria.
 C3b is an opsonin
◦ Opsonins are molecules that bind both to
bacteria and phagocytes
◦ Opsonization increases phagocytosis by
1,000 fold.
Opsonins
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Dept of Urology, GRH and KMC, Chennai.

21. Regulation of complement system
➢ Because it is nonspecific, several
regulatory mechanisms are involved
(otherwise there would be a lot of
“collateral damage”)
➢ Many components are very labile
➢ Many regulatory proteins block activity
through binding to target
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Dept of Urology, GRH and KMC, Chennai.

22. Regulatory proteins
Complement
components
Complement
inhibitors
Complement
inactivators
•Opsonin- C3b
•MAC C5-C9
•Anaphylotoxin
s-C5a, C3a
• C1 esterase
inhibitor(C1s
INH)
• S Protein
• Factor I,
• Factor H
• Anaphylotoxi
n inativator
• C4 Binding
Protein
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Dept of Urology, GRH and KMC, Chennai.

23. Regulatory proteins
Proteins Functions
C1INH dissociates C1r2-C1s2 tetramer from
C1q and stops activation of the
classical pathway.
C4BP binds to C4b and blocks binding of
C2b
Decay-accelerating factor (DAF) bind to C4b to block C4b/C2b
complex formation
displaces Bb from C3b
accelerates decay of C3/C5
convertase.
Factor I cleaves cell membrane–associated C3b
into iC3b, C3d, and C3dg
Factor H displaces Bb from the alternate
pathway C3 convertase (C3bBb)
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Dept of Urology, GRH and KMC, Chennai.

24. • CD59
• Membrane cofactor protein:This is a cofactor for factor I–
mediated cleavage of C3b and C4b.
• CR1:This is the receptor for C3b/C4b and has an inhibitory
profile similar to DAF.
• Properdin:This stabilizes AP convertases.
• Clusterin:This blocks fluid phase MAC.
• S protein:This blocks fluid phase MAC.
• Anaphylatoxin inactivator:This inactivates C3a, C4a, and C5a.
Regulatory proteins
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Dept of Urology, GRH and KMC, Chennai.

25. Deficiency disorders
Deficiency Disease
DAF Paroxysmal Nocturnal
hemoglobinuria
C1 esterase deficiency Hereditary Angionerotic
edema
C1C2C4 SLE and collagen vascular
disease
C5 to C8 Gram negative diplococci
infections, toxoplasmosis
properdin, factor B, factor D Neisserial infections
Factor H Hemolytic uremic syndrome
C3 deficiency membranoproliferative
glomerulonephritis
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Dept of Urology, GRH and KMC, Chennai.

26. Summary:
➢The complement system comprises a group
of serum proteins which, when activated, plays
an important role in antigen clearance.
➢Elaborate regulatory mechanisms are
required to prevent damage to normal cells.
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27. Antibody Structure
 Antibodies are globular
proteins called
Immunoglobulins (Ig)
 “Y”-shaped
 Made up of 4
polypeptide chains
◦ 2 identical heavy
◦ 2 identical light
◦ connected by disulfide
bonds (-S-S-)
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Dept of Urology, GRH and KMC, Chennai.

28. Antibody Structure
 Antibodies can also be
divided into two regions
based on their function
◦ Fab (fragment, antigen
binding) region.
 Tip of the antibody
 Binds the antigen
◦ Fc (fragment, crystallizable)
region
 Base of the antibody
 Can bind cell receptors,
complement proteins and
other molecules 30
Dept of Urology, GRH and KMC, Chennai.

29. Immunoglobulin domains
• 4 (or 5) in heavy chain,
• 2 in light chain.
• Both heavy and light chains have
one variable domain at the N-
terminus
chains held together by
• disulfide bonds
• noncovalent interactions
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Dept of Urology, GRH and KMC, Chennai.

30. Variable regions are Site of antigen interaction
Hypervariable (CDR; complementarity-determining
region) site of antigen binding
Rest of domain- framework
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31. Constant-region domains
CH1 and CL
• stabilizeV regions
• contribute to antibody diversity
Hinge
• flexibility
• Fab and Fc can move around it
• present in IgG, IgA, IgD
• IgE and IgM have no hinge, instead
• a fourth C domain
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Dept of Urology, GRH and KMC, Chennai.

32. Antibody Isotype
 IgM – 1st class of circulating antibody
- found in pentameric form
 IgG - most abundant antibody
 IgA - located in the mucous membranes
- found in dimeric form
 IgD - found on surface of B-cells
- probably involved in memory cell formation
 IgE - involved in allergies, i.e. trigger release of
histamine
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Dept of Urology, GRH and KMC, Chennai.

33. Ig isotypes differ in size, protein sequence and function 35
Dept of Urology, GRH and KMC, Chennai.

34. 36
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35. IgG- most common in serum; monomeric
four subclasses
Slight differences in structure; significant
differences in function
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Dept of Urology, GRH and KMC, Chennai.

36. IgG1 and IgG3 are most active
Fix complement
Bind to Fc receptors on phagocytes
opsonization
IgG4 binds to Fc receptors; does not fix
complement
IgG2 fixes complement moderately; has
low affinity for Fc rceptors
IgG
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Dept of Urology, GRH and KMC, Chennai.

37. IgM
pentamer (or hexamer),
so 10 antigen- binding sites
produced in primary response
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Dept of Urology, GRH and KMC, Chennai.

38. IgA
• most common antibody in body- not serum,
but in secretions.
• Monomer in serum, multimer elsewhere
• helps protect portals of entry in body
• main protective antibody in breast milk
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Dept of Urology, GRH and KMC, Chennai.

39. 41
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40. IgE
•Very low concentration in serum
•Binds to Fc receptors on basophils and
mast cells
•induces hypersensitivity response
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Dept of Urology, GRH and KMC, Chennai.

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42. IgD
•Very low concentration in serum
•Function of serum IgD is not known
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43. Cytoplasmic part of membrane Ig is very short.
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44. Humoral Immunodeficiency (B cells)
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Dept of Urology, GRH and KMC, Chennai.

45. Primary B cell Deficiencies
 Genetic disorders of the B lymphocytes
 Approximately 70% of primary immunodeficiencies
Not enough Ig or too much Ig
 X-Linked Agammaglobulinemia (XLA)
 Hyper IgM Syndrome
 Selective IgA deficiency
◦ Occurs in 1:600-1:800 people
 Development of anti-IgA antibodies may lead to
severe anaphylactic reactions with blood
transfusions
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Dept of Urology, GRH and KMC, Chennai.

46. Humoral Immunodeficiency (B cells)
 Transient hypogammaglobulinemia of infancy
◦ Slow to develop normal levels of antibody
◦ Asymptomatic, minor infections
◦ Low levels of IgG, IgA (IgM usually normal)
◦ Resolves by 3-6 years
 IgA deficiency
◦ Most common humoral antibody deficiency
◦ 50-80% asymptomatic
◦ Recurrent sinopulmonary infections most frequent manifestation
◦ May have severe malabsorption (chronic diarrhea)
◦ Isolated low IgA level
◦ Increased risk of autoimmune disorders
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Dept of Urology, GRH and KMC, Chennai.

47. Bruton’s X-linked Agammaglobulinemia
 No B cells
 Child clinically well for first 6 months of life
 Recurrent upper/lower respiratory tract
infections with encapsulated bacteria (S. pneumo,
H.flu)
◦ Bronchiectasis → chronic cough/increased sputum
 Sepsis, meningitis, skin infections
 Paucity of lymphoid tissue (tonsils, adenoids)
 Markedly decreased IgG, IgA, IgM
 Treatment: IVIG, antibiotic therapy
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Dept of Urology, GRH and KMC, Chennai.

48. CommonVariable Immunodeficiency
 B lymphs don’t differentiate into plasma
cells
 Recurrent sinopulmonary infections
 Low IgG, IgA, IgM
 Treatment: IVIG
 Associated with autoimmune disease,
lymphoma
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Dept of Urology, GRH and KMC, Chennai.

49. Combined Immunodeficiency
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Dept of Urology, GRH and KMC, Chennai.

50. SCID
 Defects in stem cell maturation
 Adenosine deaminase deficiency (toxic insult to T
and B cells)
 Manifestations seen in first 3 months of life
◦ Recurrent, severe bacterial, viral, fungal, and protozoan
infections (usually respiratory infections)
◦ Failure to thrive, diarrhea, dermatitis, candidiasis
 Most have lymphopenia, decreased IgG, IgA, and IgM
◦ Diagnosis made by analysis ofT, B, and NK cell subsets
 Treatment: isolation, treat underlying infections,
bone marrow transplant
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Dept of Urology, GRH and KMC, Chennai.

51. Wiskott-Aldrich Syndrome
 X-linked recessive
 Symptoms in infancy
◦ Recurrent, severe infections
◦ Eczema
◦ Thrombocytopenia (petechiae)
 Low levels of IgM
 Increased risk for hematologic malignancy
 Treatment: manage bleeding/infections,
BMT
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Dept of Urology, GRH and KMC, Chennai.

52. Ataxia Telangiectasia
 Autosomal recessive deficiency in DNA
repair affectingT and B cells
 Progressive ataxia, telangiectasia,
variable immunodeficiency (recurrent
sinopulmonary infections common)
 Increased risk of malignancy (leukemia,
lymphoma)
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Dept of Urology, GRH and KMC, Chennai.

53. Hyper IgE (Job) syndrome
 Autosomal recessive
 Symptoms/signs
◦ Coarse facial features/skeletal abnormalities
◦ Recurrent staph infections
 Impetigo (resistant)
 Pneumonia with pneumatocele formation
◦ 3 E’s: Elevated IgE, Eosinophilia, Eczema
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Dept of Urology, GRH and KMC, Chennai.

54. Hyper IgM Syndrome
 T cell abnormality preventing IgM → IgG
 X-linked recessive (males 6 mo-1 year)
 Frequent sinopulmonary infections,
diarrhea, opportunistic infections (PCP)
 Low levels of IgG/IgA, high levels of IgM
 Treatment: Ig replacement
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Dept of Urology, GRH and KMC, Chennai.

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56. Summary of antibody features
Basic structure: two identical heavy chains,
two identical light chains
Antigen-binding and effector functions
Membrane-bound and secreted forms
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Dept of Urology, GRH and KMC, Chennai.

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Dept of Urology, GRH and KMC, Chennai.