Antigen and antibdy

1. Antibody
Dr. Rupali Mali
MBBS,MD (Microbiology)
Lecturer , Department of Microbiology
SKNMC & GH
Narhe, Pune.

2. Antigen
Any substance which ,when introduced
parentrally into the body, stimulates
the production of antibody with which
it reacts specifically & in observable
manner.
Either humoral or cell mediated
immunity

4. Specificity – Ag introduced in body
react with those particular
immunocytes which carry specific
marker for that antigen
Ab produced will react with that
particular Ag

5. Epitope
Smallest unit of antigenicity, antigenic
determinant
Small area on Ag capable of combining
complementary site on Ab or T
lymphocyte.

6. Paratope
Corresponding area on antibody which
combines with epitope is called as
paratope.

7. Epitope

8. Determinants of antigenicity
Size of Ag
Chemical nature of Ag
Susceptibility to tissue enzymes

9. Most are proteins or large polysaccharides from
a foreign organism.
– Microbes: Capsules, cell walls, toxins, viral
capsids, flagella, etc.
– Nonmicrobes: Pollen, egg white , red blood
cell surface molecules, serum proteins, and
surface molecules from transplanted tissue.
Lipids and nucleic acids are only antigenic
when combined with proteins or
polysaccharides.

10. Antibody
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.
Valency of an antibody: Number of antigen
binding sites. Most are bivalent.
Belong to a group of serum proteins called
immunoglobulins (Igs).

11. Function of Ab
Elimination of foreign antigen
Recruitment& enhancement of host
effector mechanism
 antibody levels in diagnosis
Passive administration -therapy

12. Antibody structure

13. Papain digestion

14. Pepsin digestion

15. Antibody structure
Monomer: A flexible Y-shaped molecule with
four protein chains:
– 2 identical light chains
– 2 identical heavy chains
Variable Regions: Two sections at the end of Y’s
arms. Contain the antigen binding sites (Fab).
Identical on the same antibody, but vary from
one antibody to another.
Constant Regions: Stem of monomer and lower
parts of Y arms.
Fc region: Stem of monomer only. Important
because they can bind to complement or cells.

16. Lock and Key Concept
concept of antigen-antibody reactions
is one of a key (i.e. the antigen) which
fits into a lock (i.e. the antibody).
Ab
Ag

17. Types of Abs or Immunoglobulines

18. Immunoglobulin –proteins of
animal origin
Chemically antibodies are
globulines and hence they are
called as immunoglobulines
Synthesised by plasma cells & B
lymphocytes
All antibodies are Ig. But not true
vice-versa

19. Types of Ig
IgG (Gammaglobulin)
IgM (Mu)
IgD (Delta)
IgE (Epsilon)
IgA (Alpha)

20. IgG -Monomer

21. IgG
Structure: Monomer
Percentage serum antibodies:
80%Most common
Location: Blood(12mg/ml), lymph, intestine
Molecular weight150 kDa
Half-life in serum: 23 days

22. IgG
Complement Fixation, Neutralisation,
precipitation : Yes
Diffuses easily IV & EV compartments
Placental Transfer: Yes
Known Functions: Enhances
phagocytosis, neutralizes toxins and
viruses, protects fetus and newborn.

23. IgG
Catabolic rate depends directly on
conc. Of IgG.
Passive immunisation suppresses
homologus Ab producion used in
Anti RhiD isoimmunisation
 IgG1, IgG2,IgG3,IgG4
IgG1, IgG3 activators of classical
complement pathway

24. IgM -pentamer

25. IgM
Structure: Pentamer
Percentage serum antibodies: 5-10%
Location: Blood(0.5-2mg/100ml), lymph, B
cell surface (monomer)
Half-life in serum: 5 days
Complement Fixation: Yes
Placental Transfer: No
Known Functions: First antibodies
produced during an infection. Effective
against microbes and agglutinating
antigens.

26. Pentamer, 5 H & L chains, One
molecule of J Chain
Can not spread from blood to
tissues

27. Functions of IgM
Protection against bacteraemia
Pramotes phagocytosis &
bacteriolysis by complement
activation
Primary immune response
infection
Can not cross placenta- presence
in new borne  IU infection
Major component of rheumatoid
factor

28. Agglutination,Complement fixation,
cytolytic actions.

29. IgA -Dimer

30. IgA
Structure: Dimer
Percentage serum antibodies: 10-15%
Location: Secretions (tears, saliva,
intestine, milk), blood and lymph.
Half-life in serum: 6 days
Complement Fixation: No
Placental Transfer: No
Known Functions: Localized protection of
mucosal surfaces. Provides immunity to
infant digestive tract.

31. Serum IgA & Secretory IgA
Covers microorganisms and
prevents adhesion to mucosal
surface

32. IgD - Monomer

33. IgD
Structure: Monomer
Percentage serum antibodies: 0.2%
Location: B-cell surface, blood, and lymph
Half-life in serum: 3 days
Complement Fixation: No
Placental Transfer: No
Known Functions: In serum function is
unknown. On B cell surface, initiate
immune response.

34. IgE – attaches to basophil

35. IgE
Structure: Monomer
Percentage serum antibodies:
0.002%
Location: Bound to mast cells and
basophils throughout body. Blood.
Half-life in serum: 2 days
Complement Fixation: No
Placental Transfer: No
Known Functions: Allergic reactions.
Possibly lysis of worms.

36. It is mostly distributed in
extravascular space.
IgE + mast cell serves as receptor
for allergens and parasitic antigens
Mast cells degranulated with
release of vasoactive amines
Increased IgE parasitic infection

37. Abnormal immunoglobulines
Bence Jones protein – multiple
myelome
Waldenstrom’s macroglobulinemia
– myeloma, IgM producing cell

38. Multiple myeloma
Plasma cell tumor in bone marrow
Producing excess of single class
of immunoglobulin (M proteins)
All 5 classes
 Myeloma with IgM producing cells
is called as Waldenstrom’s
macroglobulinemia

39. Bence Jones protein
Light chains of immunoglobulins
Present in urine of myeloma
patients
Either kappa or lambda
Coagulates when heated at 600
C
redisolves at 800
C

40. Cryoglobulinaemia
Presence of cryoglobulin in blood
Precipitate in microvasculature on
exposure to cold
Associated with SLE, myeloma,
macroglobulinaemia.
Made up of IgG, IgM or mixture