This document provides an introduction to immunology. It defines immunology as the study of the immune system and its functions in health and disease. The immune system recognizes, attacks, and remembers pathogens that enter the body using innate and adaptive defenses. Key events in immunology history are described, such as Edward Jenner's discovery of vaccination and the eradication of smallpox. Components of the immune system like antibodies, lymphocytes, and the complement system are introduced. The document also distinguishes between innate immunity, which provides non-specific defenses, and adaptive immunity, which has memory and specificity.

1. Introduction to ImmunologyIntroduction to Immunology
Lecture 1Lecture 1stst
Dr. Humera Kausar
(PhD Molecular Biology)

2. What is immunology?What is immunology?
 Immunology is a branch of biomedicalis a branch of biomedical
science that covers the study of allscience that covers the study of all
aspects of the immune system in allaspects of the immune system in all
organisms. It deals with the physiologicalorganisms. It deals with the physiological
functioning of the immune system in statesfunctioning of the immune system in states
of both health and diseases.of both health and diseases.
 Immunity is the body's ability to fight offImmunity is the body's ability to fight off
harmful micro-organisms –PATHOGENS-harmful micro-organisms –PATHOGENS-
that invade it, e.g.Fungi, protozoans,that invade it, e.g.Fungi, protozoans,
bacteria, and viruses are all potentialbacteria, and viruses are all potential
pathogens.pathogens.

3. Edward Jenner
(1749-1823)
&
The Discovery of
Vaccination (1796)
“Vaccinia (cowpox)”
&
“human smallpox”

4. Eradication of smallpox (1979, WHO)

5. Other historic events & important findings:Other historic events & important findings:
 L. Pasteur (1880s)L. Pasteur (1880s)
– Vaccines against cholera, and rabiesVaccines against cholera, and rabies
 R. Kock (late 19R. Kock (late 19thth
century)century)
– Infections caused by microorganismsInfections caused by microorganisms
 P. Ehrlich et al. (1890s)P. Ehrlich et al. (1890s)
– Serum factors transfer of immunitySerum factors transfer of immunity
 Behring & Kitasato (1890s)Behring & Kitasato (1890s)
– Antibodies in serum bound to pathogensAntibodies in serum bound to pathogens
 Porter & Edelman (1960s)Porter & Edelman (1960s)
– Antibody structureAntibody structure
 J. Gowans (1960s)J. Gowans (1960s)
– Immunological importance of lymphocytesImmunological importance of lymphocytes

7. Koch’s PostulatesKoch’s Postulates
1.1. Pathogen must be found in the host in everyPathogen must be found in the host in every
case.case.
2.2. Pathogen must be isolated from the host andPathogen must be isolated from the host and
grown in pure culture.grown in pure culture.
3.3. When placed in a healthy host, pathogenWhen placed in a healthy host, pathogen
produced in pure culture must cause theproduced in pure culture must cause the
disease in the host.disease in the host.
4.4. Pathogen must be isolated from the new hostPathogen must be isolated from the new host
and shown to be the original pathogen.and shown to be the original pathogen.

8. TheThe immune systemimmune system recognizes, attacks,recognizes, attacks,
destroys, and remembers eachdestroys, and remembers each
pathogen that enters the body.pathogen that enters the body.
The Immune SystemThe Immune System includes all parts of theincludes all parts of the
body that help in the recognition andbody that help in the recognition and
destruction of foreign materials. White blooddestruction of foreign materials. White blood
cells, phagocytes and lymphocytes, bonecells, phagocytes and lymphocytes, bone
marrow, lymph nodes, tonsils, thymus, andmarrow, lymph nodes, tonsils, thymus, and
your spleen are all part of the immuneyour spleen are all part of the immune
system.system.
Immune system

9.
Immune system
Organ of
Immune
System
Cells Of
Immune
System

10. V
Organ of Immune System

11. Cells Of Immune System

12. Types of ImmunityTypes of Immunity
 Innate immunityInnate immunity
– ““Innate” because shared by all animalsInnate” because shared by all animals
(vertebrates and invertebrates)(vertebrates and invertebrates)
– Pre-existingPre-existing
– Non-specificNon-specific
 Adaptive immunityAdaptive immunity
– ResponsiveResponsive
– SpecificSpecific

13. 1313
The immune system protects organisms with
layered defenses of increasing specificity
 Most simply,Most simply, 1. physical barriers1. physical barriers preventprevent
pathogens such as bacteria and viruses frompathogens such as bacteria and viruses from
entering the bodyentering the body
 If a pathogen breaches these barriers, theIf a pathogen breaches these barriers, the 2. innate2. innate
immune systemimmune system provides an immediate, but non-provides an immediate, but non-
specific responsespecific response
– Innate immune systems are found in all plants and animalsInnate immune systems are found in all plants and animals
 If pathogens successfully evade the innate response,If pathogens successfully evade the innate response,
vertebrates possess a third layer of protection, thevertebrates possess a third layer of protection, the 3.3.
adaptive immune systemadaptive immune system

14. Overview of the Immune SystemOverview of the Immune System
Immune System
Innate
(Nonspecific)
Adaptive
(Specific)
Cellular
Components
Humoral
Components
Cell-Mediated
Humoral
(Ab)

15. Innate & adaptive mechanisms work together in a
cohesive fashion

16. Innate ImmunityInnate Immunity
 Protection against infection that relies onProtection against infection that relies on
mechanisms that exist before infectionmechanisms that exist before infection
– First line of defenseFirst line of defense
 BarriersBarriers
– Skin (epidermis and dermis)Skin (epidermis and dermis)
– Mucous membranes: respiratory, GI,Mucous membranes: respiratory, GI,
genitourinary tractsgenitourinary tracts
– Lacrimal apparatus: tearsLacrimal apparatus: tears
– SalivaSaliva
 ChemicalChemical
– Sebum: acidsSebum: acids
– Perspiration: lysozymePerspiration: lysozyme
– Gastric juiceGastric juice
– UrineUrine

17. Innate ImmunityInnate Immunity
 Protection against infection that relies onProtection against infection that relies on
mechanisms that exist before infectionmechanisms that exist before infection
– Second line of defenseSecond line of defense
 PhagocytosisPhagocytosis
 InflammationInflammation
 ComplementComplement
 IntererronIntererron

18. First line of defenseFirst line of defense

19. The SkinThe Skin
Serves both as mechanical and
Chemical barrier.
Microorganisms normally
Associated with skin prevent
Potential pathogens from
Colonizing.
Sebaceous glands secrete
Fatty acids and lactic acid
Which lower the skin pH
(pH 4-6).
Unbroken skin is a contiguous
Barrier.

20. Mucosal membranesMucosal membranes
Mucosal membrane consist of epithelial layerand under lying
connective tissue layer.
Mm of respiratory tract contains hair like projections called celia.that
remove microbes inhaled through the nose and mouth.
Mucus secreted by Goblet cells prevent the microbes from associating
Too closely with the cells
Mucous membrane’s microbicidal activity is owed due to the precence
of Lysozyme ,Mucopeptide and Secretary immunoglobulins A.
.

21. Lacrimal apparatus; TearLacrimal apparatus; Tear
Lacrimal apparatus is the physiologic system containing the
orbital structures for tear production and drainage.

22. Lacrimal apparatusLacrimal apparatus
Tear mechanically remove the foreign partical and also
contains,
Lysozyme which constantly baths surface of the eye.
(also found with egg whites and the female urogenital
tract, and saliva)
Lysozyme breaks the glycosidic bonds between the
NAG and NAM that make up the backbone of
peptidoglycan—causing bacteria to lyse.

23. Saliva
Saliva mechanically washes pathogens off your teeth,
and reduces the # of pathogens.
Saliva contain an antibody called secretory
immunoglobulin A, or “SIgA” which coats and protects
every tooth from harmful bacteria that may cause
decay.

24. Second line of defenseSecond line of defense

25. Phagocytosis

26. Phagocytosis

28.  Inflamation causescauses
 Redness - due to capillary dilation- due to capillary dilation
resulting in increased blood flowresulting in increased blood flow
 Heat - due to capillary dilation resulting in- due to capillary dilation resulting in
increased blood flowincreased blood flow
 Swelling – due to passage of plasma– due to passage of plasma
from the blood stream into the damagedfrom the blood stream into the damaged
tissuetissue
 Pain – due mainly to tissue destruction– due mainly to tissue destruction
and, to a lesser extent, swelling.and, to a lesser extent, swelling.

29. Complement system
 ~20 different proteins that work together to destroy~20 different proteins that work together to destroy
invaders and recruit immune cellsinvaders and recruit immune cells
 Activated three different waysActivated three different ways
– ““Classical” pathway: by antibodies bound to pathogenClassical” pathway: by antibodies bound to pathogen
(vertebrates only)(vertebrates only)
– ““Alternative” pathway: by bacterial surfacesAlternative” pathway: by bacterial surfaces
– Lectin activation pathway: by binding of mannose-Lectin activation pathway: by binding of mannose-
binding lectin (MBL) to yeast, bacteria, parasites orbinding lectin (MBL) to yeast, bacteria, parasites or
viruses (e.g., HIV)viruses (e.g., HIV)
 Activation of complement system is tightlyActivation of complement system is tightly
regulated because end results can be dangerousregulated because end results can be dangerous

31. InterferonInterferon
 Interferons are proteins, immunologist prefer toInterferons are proteins, immunologist prefer to
call them cytokinescall them cytokines
– They are glycosylatedThey are glycosylated
 The name originates from the fact that theyThe name originates from the fact that they
interfere with viral infectioninterfere with viral infection
 Cells producing IFNsCells producing IFNs
– Plasmacytoid DCs (major producers of IFN-Plasmacytoid DCs (major producers of IFN- αα
and IFN-and IFN- ββ))
– Fibroblasts and epithelial cellsFibroblasts and epithelial cells
– Macrophages and Th1 CellsMacrophages and Th1 Cells

32. Interferon Antiviral ActivityInterferon Antiviral Activity

33. Adaptive Immunity:
Characteristics
 SpecificitySpecificity: directed at specific targets: directed at specific targets
 SystemicSystemic: not restricted to initial site of infection /: not restricted to initial site of infection /
invasioninvasion
 MemoryMemory: after initial exposure & activation, a: after initial exposure & activation, a
more rapid & more vigorous response is made tomore rapid & more vigorous response is made to
subsequent exposures to pathogenssubsequent exposures to pathogens

34. Adaptive Defenses: Components
 Humoral ImmunityHumoral Immunity:: (antibody mediated immunity)(antibody mediated immunity)
provided by antibodies floating free in body fluidsprovided by antibodies floating free in body fluids
 Cell mediated immunity:Cell mediated immunity:
– lymphocytes directly attack specific invaders bylymphocytes directly attack specific invaders by
lysis or indirect attack by initiating inflammationlysis or indirect attack by initiating inflammation
and/or activating other lymphocytes &and/or activating other lymphocytes &
macrophagesmacrophages

37. Antigens vs AntibodiesAntigens vs Antibodies
 AntigensAntigens areare macromolecules that elicit an
immune response in the body and can
specifically bind with antibody. The most
common antigens are proteins and
polysaccharides.
 AnAn antibodyantibody is a “Y” shaped proteinis a “Y” shaped protein
produced in response to an antigen.produced in response to an antigen.

38. Antigens vs ImmunogenAntigens vs Immunogen
An immunogen refers to a molecule that is
capable of eliciting an immune response, whereas
an antigen refers to a molecule that is capable of
binding to the product of that immune response
(Ab). So, an immunogen is necessarily an antigen,
but an antigen may not necessarily be an
immunogen - The terms immunogen and antigen
are often used interchangeably but the later is
more common.

39.  AntigensAntigens can enter the body from the environment.can enter the body from the environment.
These includeThese include
1) inhaled macromolecules (e.g., proteins on cat hairs1) inhaled macromolecules (e.g., proteins on cat hairs
that can trigger an attack ofthat can trigger an attack of asthmaasthma in susceptiblein susceptible
people)people)
2) ingested macromolecules (e.g., shellfish proteins that2) ingested macromolecules (e.g., shellfish proteins that
trigger antrigger an allergic responseallergic response in susceptible people)in susceptible people)
3) molecules that are introduced beneath the skin (e.g.,3) molecules that are introduced beneath the skin (e.g.,
on a splinter or in an injectedon a splinter or in an injected vaccinevaccine))
AntigensAntigens

40. Properties of AntigenProperties of Antigen
1. Antigenic Determinant
2. Foreignness
3. Complexity
4. Molecular Size
5. Charge
6. Solubility
7. Accessibility
8. Valency

41. Properties of AntigenProperties of Antigen
1) Antigenic Determinant:
A site on an antigen
molecule to which an
antibody molecule binds.
Also called epitope.

42. Properties of AntigenProperties of Antigen
1. Antigenic Determinant:

43. Properties of AntigenProperties of Antigen
2. Foreignness
An antigen must be foreign or alien to the host with
which it makes contact.
The greater the phylogenetic difference, the more
Foreign something becomes.

45. Properties of AntigenProperties of Antigen
2) Foreignness
a. Autologous antigens are found within the same individual; that is,
they are not foreign to that individual. For example, a skin graft from an
individual's thigh to his chest is an auto graft, and is not foreign.
b. Syngeneic antigens are found in genetically identical individuals
(e.g., individuals from an inbred strain of mice of identical twins). A graft
between members of an inbred strain is a syngeneic graft or an isograft,
and is not foreign.
c. Allogeneic antigens (alloantigens) are found in genetically
dissimilar members of the same species. For example, a kidney transplant
from mother to daughter is called an allograft or a homograft, and it is
foreign.

46. Properties of AntigenProperties of Antigen
3. Complexity
Just because a molecule is large, if its a polymer of a single
amino acid or sugar it tends to lack immunogenicity.
complexity of a molecule increses its immunogenicity

47. Properties of AntigenProperties of Antigen
4. Molecular Size
Molecular weight greater than 10,000 daltons are excellent Antigens
Insulin(5700 daltons) and (3600 daltons) are immunogenic
BUT
Gelatin with molecular weight of 10,000 is poor immunogen.Why?
5. Charge
Net surface charge of antigen has no effect. But a significant
Property b/c net surface charge of antigen determines the net
surface charge of an Antibodies.

48. Properties of AntigenProperties of Antigen
6. Solubility
A chemical compound exhibit a high class of antigenesity if it is
highly degradable and soluble. e.g natural antigens. Synthetic
polymers fail to initiate an immune response.

49. Properties of AntigenProperties of Antigen
7. Accessibility
More accessible the antigenic determinants to the immune
cells more power full immune response will developed.

50. Properties of AntigenProperties of Antigen
8. Valency
The combining capacity of an antigen with specific
antigen binding sites of an antibody molecule is the
antigenic valency.

51. Chemical and physical classes ofChemical and physical classes of
AntigenAntigen
(2) Chemical composition and structure(2) Chemical composition and structure
Protein>polysaccharides, nucleic acids, lipidsProtein>polysaccharides, nucleic acids, lipids
(Protein containing aromatic amino acid,such as(Protein containing aromatic amino acid,such as
tyrosine)tyrosine)other examplesother examples ??
(3) Physical nature(3) Physical nature
Polymer > MonomerPolymer > Monomer
Cycle molecule >linear moleculeCycle molecule >linear molecule
Particulate Ag> soluble AgParticulate Ag> soluble Ag
ExamplesExamples??

52. 1. Haptens are partial antigens. That is:
a.Haptens are antigenic: they can react with immune
lymphocytes or antibodies.
b. However, haptens are not immunogenic: they can not
by themselves cause the production of immune
lymphocytes or antibodies.
HaptensHaptens::

53. Haptens:
2.Haptens are usually molecules which are too small to
be immunogenic.
a.Examples?
b.if a hapten of coupled to a larger carrier molecule,
however, it becomes immunogenic.
Immunogens :possess both characteristics
Hapten + carrier = complete antigen (immunogens)

54. SuperantigensSuperantigens
Conventional Antigen
Monoclonal T cell
response
Superantigen
Polyclonal T cell response
• Definition?

55. SuperantigensSuperantigens
ExamplesExamples
– Staphylococcal enterotoxinsStaphylococcal enterotoxins
– Staphylococcal toxic shock toxinStaphylococcal toxic shock toxin
– Staphylococcal exfoliating toxinStaphylococcal exfoliating toxin
– Streptococcal pyrogenic exotoxinsStreptococcal pyrogenic exotoxins

56. TD-Ag (thymus dependent Ag )
TD-AgTD-Ag stimulate B cell to produce Ab withstimulate B cell to produce Ab with
thethe help of T cellhelp of T cell
 Most of TD-Ag are proteinMost of TD-Ag are protein
 Have many kinds of determinantsHave many kinds of determinants
 Can induce HI and CMICan induce HI and CMI
 Stimulate B cell to produce :Stimulate B cell to produce :IgGIgG, IgM,, IgM, IgAIgA
 Have immune memoryHave immune memory
 ExamplesExamples
– Microbial proteinsMicrobial proteins
– Non-self or altered-self proteinsNon-self or altered-self proteins

57. TI-Ag (thymus independent Ag)
TI-AgTI-Ag can stimulate B cells to produce Abcan stimulate B cells to produce Ab withoutwithout thethe
help of T cellhelp of T cell
 Most are polysaccharideMost are polysaccharide
 Have more same or repeat determinantsHave more same or repeat determinants
 Only induce B cell to produce IgMOnly induce B cell to produce IgM
 Can not induce CMICan not induce CMI
 No immune memoryNo immune memory
• ExamplesExamples
– Pneumococcal polysaccharide, LPSPneumococcal polysaccharide, LPS
– FlagellaFlagella

58. Factors Influencing ImmunogenicityFactors Influencing Immunogenicity
Method of AdministrationMethod of Administration
 DoseDose
 RouteRoute
– Subcutaneous > Intravenous > IntragastricSubcutaneous > Intravenous > Intragastric
 AdjuvantAdjuvant
– Substances that enhance an immuneSubstances that enhance an immune
response to an Agresponse to an Ag

59. ThanksThanks