The power-point contains summerised concept on Structures, Functions and Genetics of Immunoglobulins. It is to help my fellow undergraduate students to have a basic understanding on the topic. Kindly contact me for more materials. Thank you.

1. ANTIBODIES
BY MUSOMA JESSE

2. IMMUNOGLOBLINS
STRUCTURE AND FUNCTION

3. DEFINITION
 Immunoglobulin (Ig)
Immunoglobulins are glycoprotein molecules that are
produced by plasma cells in resonse to an immunogen
and which function as antibodies

4. GENERAL FUNCTIONS OF
IMMUNOGLOBLINS
 Antigen binding
 Effector functions:
 Fixation of complement - which
results in lysis of cells and release of biologically active molecules see
 Binding to various cell types
(Phagocytic cells, lymphocytes, platelets, mast cells, and basophils)

5. BASIC STRUCTURE OF IMMUNOGLOBLINS
 Heavy and Light Chains
 Disulfide bonds
Interchain disulfide bonds
Intrachain disulfide binds
 Variable (V) and Constant (C) Region
 Hinge Region- region at which the arms of the antibody molecule forms a Y
 Domains - Light Chain domains VL and CL
- Heavy Chain domains VH, CH1-CH3 or (CH4)
 Oligosaccharides
Carbohydrates are attached to the CH2 domain in most immunoglobulins

6. BASIC STRUCTURE OF IMMUNOGLOBLINS

7. STRUCTURE OF THE VARIABLE REGION
 Hypervariable (HVR) or complementarity determining regions (CDR)
- it is based on the comparison of the amino acids sequences of the variable
regions
- Antibodies with different specificities have different CDR’s
- Antibodies of the exact same specificity have identical CDR’s
- CDR’s are found in both the H and the L chains
 Framework regions - are the regions between the CDR’s in the variable region.
- based on their similarities, Ig VL and VH can be divided into groups and
subgroups.

8. IMMUNOGLOBULIN FRAGMENTS
- The fragments are produced by proteolytic digestion by:
 Papain – gives rise to two fragments: ( Fab and Fc )
 Pepsin – gives rise to ( F(ab)2 )

9. IMMUNOGLOBULIN FRAGMENTS
 Fab
– produced by digestion with papain
- it is due to reaking at the hinge region before H-H inter-chain disulphide
bond
- Contain the light chain and the VH and CH1 domains of heavy chain.
- It is for antigen binding

10. IMMUNOGLOBULIN FRAGMENTS
 Fc
– also is due to papain digestion.
- Contains the remainder of the two heavy chains each containing a CH2 and CH3
domain.
- It is easily Crystallized
- Perfom effector functions

11. IMMUNOGLOBULIN FRAGMENTS
 F(ab)2
– due to cleavage by the pepsin
- The cleavage is for heavy chain after the H-H inter-chain disulphide bonds
- This results in a fragment that contains both antigen bind sites(Fab)
- It is named so because it was divalent
- It binds antigen but it does not mediate the effector functions of antibodies.

12. IMMUNOGLOBULIN FRAGMENTS

13. HUMAN IMMUNOGLOBULIN CLASSES,
SUBCLASSES, TYPES AND SUBTYPES
 Immunoglobulin Classes
- they are 5 classes
- They are based on differences in the amino acid sequences in the CH
- All Ig within a given class have a very similar heavy chain constant regions
- They include:
 IgG - Gamma heavy chains
 IgM - Mu heavy chains
 IgA – Alpha heavy chains
 IgD - Delta heavy chains
 IgE - Epsilon heavy chains

14.  Immunoglobulin Subclasses
– based on the small differences in the amino acid sequences in CH chains.
- Examples include:
- IgG Subclasses Ig amma heavy chains Ig amma heavy chains
Ig amma heavy chains Ig amma heavy chains Ig Subclasses
Ig lha heavy chains Ig lha heavy chains

16. Structure and some properties of IG
clasess and subclasses
1. IgG
- Monomer
- Major serum level
- Major ig in extravascular space
- Placental transfer( except IgG2)
- Fix complement( except IgG4)
- Binding to cells (except IgG2 and IgG4)

17.  2. IgM
- Pentamer
- Extra domain (Ch4)
- Has J chain( involves in polymerisation of the molecules into a pentamer)
- 3rd most common serum Ig
- First to be made by the fetus
- Fix complement
- Good agglutinating Ig
- Binding to cells
- B cell surface Ig

18. 3. IgA
– monomer in serum but dimer in secretions
- Has secretory piece ( T )piece – It helps in transportation across mucosa
- protects the degradation of IgA in the secretion
- J chain present when it exists as a dimer
- 2nd most abundant
- Major Ig in secretions
- Donnot fix complement unless aggregated
- Can bind to some cells ( PMN)

19. 4. IgD
– monomer
- Found in low levels in the serum
- Primarily found in B cell surface
- Donnnot fix the complement

20. 5. IgE
– Monomer
- Extra domain in constant region
- Least common serum IgG ( bcoz it tightly bind to Fc receptors of mast cell even
interacting with the Ag)
- Involved in allergic reactions
- Plays a role in Parasitic helmith disease
- Don't fix the complement

21. ISOTYPES
- It is an antigenic determinant that x-sterize classes and subclasses of heavy chain
and types and subtypes of light chain
- Location - Fc portion in heavy portion
- constant region of light chain
- Importances :
 Quantifying Ig classes and subclasses in various diseases ( anti-Isotypes)
 Characterisation of B cell leukemia
 Dx of various immunodefiency disease

22. ALLOTYPES
- Are antigenic determinant specificied by allelic forms of the leg genes
- Rep structural difference in the constant region
- All are not founf in all members of the species
- Location – Constant region of heavy and light chain
- Examples: GIm (3), GIm ( 17) Km (1) and Km(3)
- Importance:
 Monitoring bone marrow grafts
 Forensic medicine
 Paternity testing

23. IDIOTYPES
- Are antigenic determinant created br hypervariable regions ( combining site) of the
antibody.
- Location – Fab fragment(near HVR of heavy and light chain)
- Importances:
 V- region marker
 Regulation of immune response
 Vaccines ( by use of anti- idiotypes antibodies that stimulate B cell to release Ab
used as vaccine)
 Rx of B cell tumors ( use of Ab directed to idiotype on malignant Bcell)

24. GENETICS OF
IMMUNOGLOBULINS

25. LIGHT CHAIN GENE FAMILIES
Germ line gene organization

26. LIGHT CHAIN GENE FAMILIES
- Each of the V region genes is composed of two exons :
 L – codes for Leader region
 V – codes for the most of variable region
- C gene has also additional exon J (joining)
- L, V, J and C exons are separated by introns. i.e ( Promoter (P) and Enhancer (E) )

27. LIGHT CHAIN GENE FAMILIES
Gene rearrangement and expression
- A cell commits to become a B cell making a light chain
- Rearrangement of the genes ( exons)
- one of V genes are brought near next to one of J region…due to removal of introns
between V and J
- Promoter (P) is brought to an Enhancer(E)
- Gene becomes transcriptionally active
- Transcription initiates making a Pre- mRNA ( L, V J and C and introns)
- Slicing of introns – results to L, V, J and C)
- Translation of mRNA in the cytoplasm to remove L region
- Protein is transported into the lumen of ER
- Light chain is assembled with heavy chain and Ig is secreted.

28. LIGHT CHAIN GENE FAMILIES
Gene rearrangement and expression

29. HEAVY CHAIN GENE FAMILY
Germ line gene organization
 C genes
 V region
 L region
 J region
 D region ( diversity)
 introns

30. HEAVY CHAIN GENE FAMILY
Gene rearrangements and expression
- The cell commits to become B cell making a heavy chain
- Rearrangements of DNA at 2 levels due to removal of introns:
 one of the D region is brought next to one of J region
 One of the V genes is brought next to the rearranged DJ region
- Promoter is brought closer to enhancer
- The gene becomes transcriptically active
- Initiation of transcription and mRNA is formed ( L, V, D,J Cmu and Cdelta and
intons)

31. HEAVY CHAIN GENE FAMILY
Gene rearrangements and expression

32. HEAVY CHAIN GENE FAMILY
Gene rearrangements and expression
- Splicing of introns found between C genes
- Processing of pre-mRNA by 2 ways:
 to bring the VDJ next to the Cmu gene
 to bring the VDJ next to the Cdelta gene
- The resulting mRNAs have the L, V, D, J and Cmu or Cdelta exons
- Translation in the cytoplasm where L is removed
- Protein is transported to ER
- Assembling of heavy chain with light chain and Ig is secreted.
- V gene codes for V region
- D, J and C code for sequences in the C gene.

33. HEAVY CHAIN GENE FAMILY
Gene rearrangements and expression

34. MECHANISM OF DNA REARRANGEMENT

35. MECHANISM OF DNA REARRANGEMENT
- RSS are unique sequences flanking the V,J and D exons which function in
recombination
- Each RSS consist of : nonamer and heptamer separated by either 12 or 23 base
pairs
- Spaces btn the base pairs corresponds to 2 turns of DNA helix
- Recombination occurs only btn 1 and 2 turns signal
- Lambda Light chain – 1 turn signal at J exon, 2 turn signal at Vlambda
- Kappa Light Chain – 1 turn at Vkappa gene and 2 turn at J exon
- Heavy chain – 1 turn on each D side and 2 turn at both V and Jexons.

36. MECHANISM OF DNA REARRANGEMENT
- Recombination results in removal of introns between V and J( for light chain) or V,
D and J ( for heavy chain)
- Enzymes involved: RAG-1 and RAG-2
- Mutations in the gene result in severe immunodeficiency disease( both T and B
are deficient)

37. ORDER OF GENE EXPRESSION IN
IMMUNOGLOBULIN GENE FAMILIES

38. ORDER OF GENE EXPRESSION IN
IMMUNOGLOBULIN GENE FAMILIES

39. TEST QUESTIONS
1. Antibodies are
a) proteins
b) glycoproteins
c) carbohydrates
d) nucleic acid
2. Antibodies consists of
a) 2 light chains and 2 heavy chains arranged in a Yshaped configuration
b) A light chain and 2 heavy chains arranged in a Yshaped configuration
c) 2 light chains and a heavy chain arranged in a Yshaped configuration
d) all of these

40. 3. Light chains and heavy chains are joined by
a) covalent bond
b) hydrogen bond
c) disulphide bond
d) ionic bond
4. The antigen binding site on an antibody is called
a) antitope
b) epitope

41. c) paratope
d) endotope
5. An antibody has
a) 2 Fab regions and an Fc region
b) an Fab region and an Fc region
c) 2 Fab regions and 2 Fc regions
d) many Fab regions and many Fc regions

42. 6. The hypervariable region resides in the
a) N terminal region of light chain
b) Nterminal region of light and heavy chain
c) Cterminal region of light chain
d) Cterminal region of light chain and heavy chain
7. Fab stands for
a) fragment antibody binding
b) fragment antigen binding
c) fragment antibody or antigen binding
d) fragment affinity binding

43. 8. Which of the following statement is true regarding Fc region
a) fragment crystalisation and is the constant region
b) fragment constant and is the variable region
c) fragment crystalisation and is the variable region
d) fragment crystalisation and has both variable and constant region
9. Fab region
a) has a hypervariable region that binds with antibody
b) has a hypervariable region that binds with antigen
c) has a hypervariable region that binds with other immune cells
d) all of these

44. 10. Fc region is involved in
a) cell surface receptor binding
b) complement activation
c) determining diffusivity of antibody molecule
d) all of these
11. The ability of antigen to stimulate antibody production is called
a) affinity
b) Antigenicity
c) elicitation
d) none of these

45. 12. Light chains and heavy chains of antibodies are joined by
a) hydrogen bond
b) hydrophobic bond
c) disulphide bond
d) ionic bond
13. Clearance of antigens by antibodies involve
a) neutralization and agglutination
b) opsonisation and complement activation
c) precipitation
d) all of these

46. 14. The two identical light chains of an antibody belongs to
a) kappa only
b) lambda only
c) lambda or kappa
d) none of these
15. The hypervariable region of antibody consists of
a) 510 aminoacids that form antigen binding site
b) 50100 aminoacids that form antigen binding site
c) 5-10 aminoacids that forms the antibody binding site
d) a part of constant region of heavy and light chain

47. 16. Which of the following is the most abundant immunoglobulin g)
a) IgM
b) IgG
c) IgA
d) IgE
17. . Which of the following g is targeted against polysaccharides of encapsulated bacteria
a) IgG1
b) IgG2
c) IgG3
d) IgG4

48. 18.. g consists of
a) 2 light chains and two heavy chains joined by disulphide bond (H2L2)
b) 2 light chains and two heavy chains joined by hydrogen bond (H2L2)
c) 2 light chains and a heavy chain joined by disulphide bond (H1L2)
d) a light chain and two heavy chains joined by disulphide bond (H2L1)
19. Which is the g that can cross placenta and provide passive immunity to new born
a) IgM
b) IgG
c) IgA
d) IgE

49. 20. Which is the g that first reaches the site of infection
a) IgM
b) IgG
c) IgA
d) IgE
21. Which is the largest g
a) IgM
b) IgG
c) IgA
d) IgE

50. 22. Which of the following statements are true regarding gM
a) IgM is a pentamer and is the largest Ig and called as natural antibody
b) IgM exists as monomer on Bcell surface
c) IgM is involved in early primary immune response
d) all of these
23. Which of the following statements are true
a) IgM is involved in primary immune response
b) IgG is involved in primary immune response
c) Both IgM and IgG are involved in primary immune response
d) IgG is involved only in secondary immune response

51. 24. The antibody present in secretions like tears saliva colostrum is
a) IgM
b) IgG
c) IgA
d) IgE
25. The primary g of eocrine secretions is
a) IgM
b) IgG
c) IgA
d) IgE

52. THANK YOU