definition of immunity, classification , examples, antibody & antigen, antibody mediated immunity

1. IMMUNITY
Dr. F.B Irani

2. Objective
Definition
Types of immunity
Concept of Ag and Ab
Humoral immunity- B lymphocytes
The complement system

3. § Immunity – it is the resistance of the body
against pathogenic agents.
§ Immune response – two ways:
1.Humoral or antibody-mediated immunity (AMI)
2.Cell-mediated immunity (CMI)
§ Autoimmunity – response to self-antigen.
§ Hypersensitivity – abnormal immune response
which produces damage in the host.

4. Cytokines-
hormone-like molecules that act in paracrine
fashion to regulate immune response.
They are secreted lymphocytes, macrophages,
endothelial cells, neuroglial cell.
Types= Interleukins(IL 1-13), CSF,
tumor necrosis factors(TNFα, β ),
interferon's(IFN α, β γ).

5. classification
Innate immunity acquired immunity
Non-specific specific Active Passive
. Species .Natural . Natural
. Racial . Artificial . Artificial
. individual

6. INNATE IMMUNITY
It is inborn capacity due to genetic and constitutional
make up of individual.
Mechanisms – 1. intact skin, mucosa, hairs, cilia, urine.
2. saliva, acidic gastric juice and tears.
3. substances in body fluid like lysozyme, polypeptides,
complements, interferons.
4. Phagocytic cells (neutrophilis, monocytes) , natural
killer cells(lymphoctes), Eosinophils, macrophages.

7. Acquired immunity
- resistance that is acquired during life time.
Two types:- 1) Active immunity- Ab and
immunocompetent cells are produced by
individual’s own immune system.
a) Natural active immunity- result from a
subclinical or clinical infection. e.g. immunity for
poliomyelitis.

8. b) Artificial active immunity – induced by
introducing antigen in the body in form of
vaccines (active immunisations).
e.g. -BCG, TAB
– Tetanus, Diphtheria toxoid,
- MMR, vaccines for yellow fever,
poliomyelitis, rabies.

9. 2) Passive immunity – immunity that is
transferred to a recipient in a ready-made form.
- No role of individual’s immune system.
Natural passive immunity – transfer of ready made
antibodies from the mother as:-
- IgG to fetus through the placenta,
- IgA are passed in colostrum after birth.

10. b) Artificial passive immunity – transferred
to the recipients by injecting ready made
antibodies.
- Injection of ATS , ADS,AGS.

11. ANTIGENS
-These are the substances that can stimulate an
immune response in the body.
Ag may be micro-organism or part of it like capsule,
flagella, cell wall, transplanted tissue, Pollen, eggs
white, blood cells.
- Nature- protein, some are nucleoproteins,
Glycoproteins and polysaccharides.
- T cells respond to protein Ag,
- B cell to proteins & non proteins.

12. Ag has two properties -
Immunogenicity :- to provoke an immune response.
Reactivity :- react with an antibody or a cell or both.
Hapten or incomplete antigen –
- Ag that has reactivity but lack immunogenicity
- When combined with larger molecules (proteins)
show response.

13. Determinant site
(epitopes)
Structure of an antigen

14. Major histocompatibility complex (MHC)-
- Are self antigens, help in identifying & reject the
foreign antigens, & present to T cell for cellular
immunity.
-Also called HLA(human leucocytes associated
antigens).
- They are encoded by genes.
- No two persons can have same MHC proteins.

15. Two subclasses of MHC genes
MHC classⅠ- found on all cells of body except RBCs.
MHC Ⅰ picks up peptide fragments with 8-10 AA.
MHC class Ⅱ- found on APCs(Ag presenting cells),
activated T cells and thymus cells.
-MHC Ⅱ picks up peptide fragments with13- 17 AA.

16. ANTIBODIES
Antibodies – (immunoglobulin) are gamma
globulins which are produced in response to
Ag stimulation.
- Igs are divided into five classes or isotypes -
IgG, IgA, IgM, IgD and IgE

17. Basic Antibody Structure

18. IgG
 -It is most abundant present in intra and extra
vascular pool.
 It can cross placenta.
 It provides natural passive immunity.
 They serve as opsonins and promotes
phagocytosis of bacteria.

19. IgA
 It is formed by mucosal and submucosal
aggregates of lymphoid tissue. Then transferred to
epithelial cells.
 Provides defense mechanism in mucosa of GIT,
Lungs, UT.

20. IgM
 It is earliest to be synthesized
 It activates complement system.
 They are produced in primary immune response.
 They form Ab of ABO blood group

21. IgD
 Present on surface of B lymphocytes.
 It is involved in antigen recognition.
IgE
They mediate allergy, hypersensitivity and
anaphylaxis.
Produced in lining cells of respiratory and GIT.
They releases histamine from basophils and
mast cells.

22. DEVELOPMENT OF IMMUNE RESPONSE
B-lymphocytes T-lymphocytes
Humoral immunity
Defence against
bacterial & virus
that infect
respiratory &
intestinal tract
Cellular immunity
Defence against
fungi, viruses,
bacteria, & tumors.
aa
During foetal development
‘Lymphocyte precursors’ from
bone marrow

23. TYPES OF IMMUNE RESPONSES
Two types-
Primary response-
- introduced into the body for the first time.
- Always latent period from 4 days to 4 weeks.
Secondary response-
- introduced into the body on a second occasion. It
occurs more quickly and more intensely.

24. ROLE OF HUMORAL IMMUNITY
1. Defence against extracellular bacterial pathogens
and viruses.
2. Participates in immediate hypersensitivity
reactions of typeⅠ,Ⅱand Ⅲ
3.Associated with autoimmune diseases.

25. STAGES OF HUMORAL IMMUNE RESPONSE
1. Antigen processing and presentation
2. Recognition of antigen by lymphocytes
3. Lymphocyte activation(both T and B)
4. Differentiation of B cell into plasma cell
5. Production of antibodies by plasma cells
6.Inactivation of antigen
7. Formation of memory B cells

26. v
Antigen(bacterium)
Macrophage MHCⅡ
Antigen presenting cell
Antigen processing
TCR
Sensitized T cell
Processed antigen Slgs
mlgs
Sensitized B cell
Receptors
Blast cell
Helper Plasma cell
Memory cell
Humoral immunity

27. Antigen
Macrophages (MHC Ⅱ)
Blast transformation
B lymphocytes T lymphocytes
(CD4 ) helper T cells
T-B co-operation
Plasma cells 1. interleukins 2 (IL2)
Memory B cells 2. B cell growth factor

28. Plasma cells Memory B cells
2000 Mol/sec
IgG IgA IgM IgD Ig E
Direct attack Attack through complement system
Agglutination CLASSICAL ALTERNATIVE
Precipitation (C1 to C9, B and D) (properdin pathway)
Neutralization Neutralization activate C3 and C5
Cytolysis Agglutination
Cytolysis
Chemotaxis
Opsonization

29. THE COMPLEMENT SYSTEM
These are group of plasma proteins which complement
the effects of antibodies in destroying antigen.
They are designated as C1-C9. C1 into C1q, C1r, C1s.
(Total is 11)
Mechanism of complement activation:-
The classical pathway-
The alternative pathway-
The Mannose-Binding Lectin pathway-

30. SAQ:-
1.Active immunity, 2. Passive immunity
3. Innate immunity, 4.Cellular immunity,
5. Acquired immunity, 6. Immunoglobins,
7. Functional lymphoctes,
8. Humoral immunity 9. Autoimmunity,
LAQ:-
1. Describe role of T lymphocytes in immunity.
2. Describe role of B lymphocytes in immunity.
3. Describe innate immunity.
4. Describe different types of immunoglobins.

31. Thank you