This document discusses antibodies, including their definition, history, structure, classes, and theories of production. Some key points: - Antibodies are proteins called immunoglobulins that are produced by plasma cells to identify and neutralize pathogens like bacteria and viruses. - The basic antibody structure consists of two heavy chains and two light chains that form sites for antigen binding. There are five classes of antibodies (IgG, IgM, IgA, IgD, IgE) that differ in structure and function. - Early theories on antibody production included the instructive theory (direct/indirect template theories) and selective theory (side chain, natural selection). The clonal selection theory, introduced by Burnet

1. ANTIBODIES
by
Dr. Priti D.Diwan
Assistant Professor
Department of Zoology
J.D.Patil Sangludkar Mahavidyalay Daryapur

2. Definition
 Antibody is a large protein ,constitiutes γ-gloublin
produced by plasma cells
 It is used by the immune system to identify and
nutralize pathogens such as bacteria and viruses
 Antibodies are also called Immunogloublins
 The antibody recognizes a unique molecule of the
harmful agent called ANTIGEN,via the variable
region

3. History
 In 1940s some facts are recognised :
 Antibodies is genrally bivalent
 Antibodies contains hapten ,it is a heterogenous
with respect to affinity
 Antibodies are different classes based on Ultra
Centrifugation,Electrophorosis

4. STRUCTURE
 All antibodies share a basic structure
 Antibodies are heavy globular plasma
proteins[or]glycoproteins
 The attached glycans are critically important to
the structure and function of the antibody
 Each antibody is heterodiamer with a molecular
weight of approximately 150KD

5. Basic structure of Antibody

6. IMMUNOGLOBULIN
DOMAINS
 Antibody is composed of two identical heavy
polypeptide chains and two identical light
chains,bonded via interchain disulphide[s-s]
linkages
 Each chain is composed of structural domains
called Immunoglobulin domains
 These domains contains about 70-110
aminoacids

7. HEAVY CHAINS
 Five types of heavy chains are present
 They are;1)alpha(α) 2)gamma(γ) 3)delta(Δ)
 4)epsilon 5)mu(μ)
 Each heavy chain has two regions,one constant
region and one variable region
 Alpha and gamma chains contains approximately
450 aminoacids, where as mu and epsilon chains
have approximately 550 aminoacids

8. LIGHT CHAINS
 Two types of light chains are present
 They are;1)kappa 2)lambda
 All antibodies have one of the two kinds of light
chains
 A light chain has two successive domains,one
constant domain and one variable domain
 The approximate length of a light chain is 211-217
aminoacids

9. Sites of Immunogloublin

10. DIFFERENT CLASSES OF
ANTIBODIES
 There are five classes of antibodies are present
 They are;1)IgG 2)IgM 3)IgA
 4)IgD 5)IgE
 The antibody classes are named as correspond
to their heavy chain types

11. 1)IgG
 They makes up approximately 80% of the serum
antibodies
 They has a half-life of 7-23 days
 IgG is a monomer and has 2-epitope binding sites
 This is the only class of antibodies that can cross
the placenta and enter the fetal circulation

12. Functions
 Immunity to new born
 Neutralisation of Toxins
 IgG3 binds to Fc receptor by Phagocytosis

13. 2)IgM
 They makes up approximately 13% of the serum
antibodies
 They has a half-life of about 5 days
 Most of the IgM are pentamer and has 10 -
epitope binding sites.some are momomer
 It is the first immunoglobulin class produced in a
primary response to antigen

14. functions
 Activation of classical pathway
 Defence against multivalent antigens
 Act as Opsonin

15. 3)IgA
 They makes up approximately 6% of the serum
antibodies
 They has a half-life of approximately 5 days
 IgA is a dimer and has 4-epitope binding sites
 They found mainly in body secretions such as
saliva,mucous,tears,colostrum and milk

16. Functions
 It as a Seceratory antibody
 Effective against virus that causing Influnza
 Production to Infant gut

17. 4)IgD
 They makes up approximately 0.2% of the serum
antibodies
 IgD is a monomer and has 2-epitope binding sites
 This class antibodies are found on the surface of
B-lymphocytes

18. Function
 B cell activation.
 Act a receptor for antigen binding

19. 5)IgE
 It was discovered by KandT Ishizaka
 It is very low concentration in blood(17-450ng/ml)
 It contain small percentage of Lympocytes

20. Functions
 Responsible for Immediate hypersensitivity
 Binds to Fc receptor on basophils and mast cells
 Release of substance like histamine ,vasoactive
mediators

21. Structures of Antibodies

23. THEORIES OF ANTIBODY PRODUCTION
INSTRUCTIVE THEORY
Direct template theory
• Indirecttemplate theory
SELECTIVETHEORY
• Sidechaintheory
• Natural selectiontheory
Clonalselectibntheory

24. Side chain theory
• Ehrlich (1900)
• Cells have surface receptors which have
capability to react with substances having
complementary side chains
• This theory is abandoned when Landsteiner
explained
Antibodies could be formed against
not only natural antigens but also against various
synthetic chemicals (riboflavin, estradiol & L-
thyroxine)

26. Direct template theory
• Breinl & haurowitz
• Alexander
• Mudd
• The antigen enters antibody forming cells and
acts as a template so that antibodies are formed
with complimentary combining sites to antigen
• Pauling 1940 specificity was determined by
folding of the antibody to form tertiary structure
fitting antigen molecule

28. Indirect template theory
• Burnet fenner 1949
• A genocopy of antigenic
determinant was in corporated in
antibody producing cell genome
and transmitted to progeny cells

29. Natural selection theory
• Jerne 1955
• Million globulin molecules are formed in
embryonic life with full range of antigenic
specificities ( natural antibodies)
• Antigen when enters it combines with nearly
matching
• This move on to the antibody producing cells
they get activated and produce same kind of
antibody

31. What clonal selection explains..?
• It explains how the cells of immune
system will react with a specific antigen
that enters body

32. Who introduced it..?
• Australian doctor Frank Macfarlane
Burnet in 1957
• Widely accepted model

33. Postulates
1. Each lymphocyte bears a single type of receptor
with a unique specificity (by V(D)J
recombination).
2. Receptor occupation is required for cell
activation.
3. The clone cells derived from an activated
lymphocyte will bear receptors of identical
specificity as the parental cell.
4. Forbidden cells will be deleted at an early stage.

34. Reference