Adaptive immunity involves both humoral and cellular responses. B-cells produce antibodies that circulate in the blood and lymph to neutralize pathogens and toxins. T-cells recognize intracellular pathogens through antigen presentation and induce cytotoxic killing of infected cells. Antibodies and T-cells are activated through antigen recognition and work together to provide long-lasting adaptive immunity against specific pathogens. Vaccines utilize this immune memory to safely induce immunity against harmful diseases.

1. Adaptive Immunity

2. Immunity: Third Line of Defense
• Red bone Marrow  Stem cells  T and B cells
• Specific reaction to microbial infection
Humoral Immunity Cell Mediated Immunity
B-cells
Recognize
Specific Antigens
Make Antibodies
against them
T-cells
Recognize
Specific Antigens
Make Cytokines
against them

3. Antigens & Antibodies
• Antigens (Antibody generators)
• proteins or large polysaccharides
• Components of invading microbes
• Non-microbial antigens:
• pollen, egg white, serum proteins, blood cells etc
• Epitopes = specific region that interacts with Ab.
• Antibodies
• globulin proteins (immunoglobulins) Y-shaped
• Made in response to antigen; bind specifically to Ag
• At least two identical sites that bind to epitopes
• Bivalent molecule

5. Bivalent antibodies binding epitopes

6. Classes of Immunoglobulin
IgG:
• Y-shaped “Monomer”
• readily cross vessel walls into inflammation site
• ~80% of serum antibodies
• Protects against bacteria and viruses
• Neutralizes toxins
• Enhances phagocytosis
• Triggers complement
• Confers immunity to fetus
AFM of a bivalent
(monomer) antibody

7. Classes of Immunoglobulin
IgM:
• Pentamer (can be monomer too)
– Too big to cross into tissue from blood
• First Antibody response to 1 response
• Dominates ABO blood group response
• Effective in Complement Activation
• Highly effective at Agglutination
– Cross-links several Antigens

8. Classes of Immunoglobulin
IgA:
• Dimer
– Serum IgA (monomer)
– Secretory IgA
• Mucus membranes and secretions
– Mucus, tears, saliva, breast milk
– Prevents pathogen attachment to mucosal surface
– Colustrum
• Decreases infant risk to GI infections
Dimeric IgA antibodies

9. Classes of Immunoglobulin
IgD:
• Monomer
• Blood, lymph, B-cell surface
• No defined function
– 0.002% serum antibodies
IgE:
• Monomer
• Allergic Reactions, Parasitic Infections
• Signals for complement and phagocytes
• Binds mast cells/basophils  histamine  allergy

11. B-cell Activation
• Stem Cells  B-cells
– Each B-cell has surface Igs against specific Ag
• Binding of specific Ag activates THAT B-cell
• Activated B-cell  clonal expansion  Plasma
cells  Antibodies
– Some activated B-cells become Memory cells

13. Antigen-antibody binding
• Antigen-Antibody Complex
– Specific interaction
• Affinity: strength of bond
• Specificity: ability to distinguish minor differences in AA
– Binds at epitope
– Complex formation tags foreign cells
• Destruction by phagocytes and complement

14. Outcomes of Ab-Ag binding
• Agglutination
– Clumping of Antigens
• Opsonization
– Ab coats microbe
– Enhances phagocytosis
• Neutralization
– prevents Ag binding host cell
• Antibody-dependent cell-mediated cytotoxicity
– Ab coats microbe
– Ab binds T-cells/NK cells/other immune cells
– Cytokines released  lyse microbe
• Complement Activation
– IgG, IgM
– Binds C1
– C1 C2, C4  C3  complementation cascade

15. T-cells and cellular immunity
• T-lymphocytes
• Combat pathogens within host cells
– Not exposed to circulating Antibodies
• Two Types
– T-helper Cells (TH: TH1 and TH2)
– Cytotoxic T-cells (Tc)
– Surface Receptors
• Glycoproteins
• CD (clusters of differentiation)

16. Antigen Presenting Cells
• B-cells
• Phagocytes
– Dendritic cells
– Macrophages
• Chew up Microbe/ Antigen
– Present parts of the Antigen on surface
– Presentation involves a phagocytic receptor
• MHC (major histocompatibility antigen)

17. The MHC-antigen complex
MHC = major histocompatibility complex
• Collection of genes that encode proteins found on all
nucleated mammalian cell membranes
• Presence of MHC identifies the host
- Keeps immune system from making antibodies
against host cells
Class II – found on APCs like B-cells
Class I – found on almost any cell of the host
• Makes it possible for cytotoxic T-cells to attack
host cells that have been altered

18. T-Helper Cells (CD4+)
- bind to MHC class II molecules
Activation of TH cells:
1. TH cell recognizes an antigen in complex with MHC class II
presented on the surface of an APC
2. TH cell proliferates and differentiates into TH1 and TH2
cells – secrete cytokines
TH1 = cytokines activate macrophages, enhance complement
TH2 = cytokines stimulate production of antibodies
important for allergic reactions, and eosinophils that protect
against extracellular parasites

19. APC (dendritic cell) and TH cell
Antigen
fragment
Antigen
MHC class II
moleculesMicrobe
T helper cell
TH cell receptor
contacting MHC-
antigen complex

20. Cytotoxic T-cells (CD8+)
• Recognize and kill altered or foreign cells
• bind to MHC class I molecules
- found on all nucleated cells
• Presented in complex with viral/parasitic antigens on
surface of infection-altered cells
Steps in destruction of target cells:
1. Recognize foreign antigen/MHC class I protein
complex on cell
2. Attaches and released perforin  pore
• Allows proteases to enter
3. Apoptosis = programmed cell death

21. Cytotoxic T-cells (CD8+)
1. Virus-infected cell with endogenous viral antigens
(inside cell)
2. Abnormal antigen is presented on cell surface in
complex with MHC class I molecules
- TC cell with receptor for that antigen binds
3. TC cell induces destruction by apoptosis
Antigen
MHC
class I
MHC-antigen
complex
Cytotoxic
T-cell

22. Apoptosis
Blebbing = external
membranes bulge outward
Top: B-cell undergoing apoptosis
Bottom: Normal B-cell for reference

23. Antigen-presenting cells
Dendritic cells = Principle APCs to
induce immune responses by T-cells
• Long extensions = dendrites
• Resemble nerve cell dendrites
1. engulf invading microbes
2. degrade them
3. transfer them to lymph nodes
for display to T-cells located
there

24. Macrophages = (large eaters)
• Innate immunity: important in
phagocytosis of apoptotic cells and
other debris
• Adaptive immunity: become
activated macrophages upon
ingestion of foreign antigen
- Appear larger and “ruffled”
1. Take in antigen
2. migrate to lymph nodes
3. present antigen to T-cells located there
Antigen-presenting cells

25. Extracellular killing
Natural killer cells = granular leukocytes that destroy virus-
infected cells, tumor cells, and parasites
• Part of innate immunity (non-specific)
- Not triggered by antigen
• Remains external to target cell
Mechanism:
1. Contact a target cell
2. Determine if it expresses MHC class I self-antigen
(*tumor cells, viral-infected cells don’t)
3. No expression  induces lysis/apoptosis (similar to
that of cytotoxic T-cell)

26. Antibody-dependent-cell-mediated
cytotoxicity
• Invaders too large to be phagocytized (euks) can
be attacked by immune cells
• Uses antibodies of humoral system
• NK cells, macrophages, neutrophils, and
eosinophils respond and kill targeted cells
Mechanism:
• Target cell coated with antibodies
• Immune cells bind to antibodies
• Target cell is lysed by secretions

27. Antibody-dependent-cell-mediated
cytotoxicity

28. Antibody-dependent-cell-mediated
cytotoxicity
Eosinophils adhering to a parasite for external attack

29. Cytokines
Cytokines = chemical messengers of immune cells
• Soluble proteins/glycoproteins
• Produced by immune cells after a stimulus
• Act only on a cell that has receptors for it
- Interleukins = cytokines that serve as communicators
between leukocytes (WBCs)
- Chemokines = induce migration of leukocytes into
areas of infection/tissue damage
- Interferons = protect cells from viral infection

30. Cytokines
- Tumor necrosis factor (TNF) = cytokines that act in
inflammatory reactions; also target tumor cells
- Hematopoietic cytokines = control development of
stem cells into red or white blood cells
Ex) Granulocyte-colony stimulating factor
• Granulocyte precursors  neutrophils
Cytokine storm = overproduction of cytokines
- Damage to host tissues

31. Extracellular antigens
A B cell binds to the
antigen for which it is
specific. A T-dependent B
cell requires cooperation
with a T helper (TH) cell.
The B cell, often with
stimulation by cytokines
from a TH cell, differentiates
into a plasma cell. Some B
cells become memory cells.
Plasma cells
proliferate and
produce antibodies
against the antigen.
Intracellular antigens are
expressed on the surface of an
APC, a cell infected by a virus, a
bacterium, or a parasite.
A T cell binds to
MHC–antigen
complexes on the
surface of the
infected cell,
activating the T cell
(with its cytokine
receptors).
Activation of
macrophage
(enhanced
phagocytic activity).
The CD8+T cell
becomes a cytotoxic
T lymphocyte (CTL)
able to induce
apoptosis of the
target cell.
B cell
Plasma cell
T cell
TH cell
Cytotoxic T
lymphocyte
CytokinesCytokines
Lysed target cell
Cytokines activate
macrophage.
Cytokines from the TH
cell transform B cells
into antibody-producing
plasma cells.
Cytokines activate T
helper (TH) cell.
Memory cell
Some T and B cells differentiate
into memory cells that respond
rapidly to any secondary
encounter with an antigen.
Humoral (antibody-mediated) immune system Cellular (cell-mediated) immune system
Control of freely circulating pathogens Control of intracellular pathogens
Figure 17.20 The dual nature of the adaptive immune system.

32. Vaccines
• suspension of organisms/ parts of organism
used to INDUCE immunity
• Artificial Active Immunity

33. Vaccine: Types
• Live attenuated whole-agent
• Inactivated whole-agent
• Toxoids
• Subunit Vaccines
– Recombinant subunit vaccines
• Nucleic acid Vaccines

34. Live attentuated Whole agent
• living but attenuated (weakened) microbes
– Mutated virus
– Related virus
• Attenuated viruses replicate in the body
– Cell and humoral immunity
• Lifelong immunity
• Counterindicated
– immune compromised
– Attenuated microbes: from mutated strains  can back-mutate to virulent
form
• Viral vaccines: MMR, Sabin polio, Smallpox, Flumist (influenza)
• Bacterial vaccines: tuberculosis

35. Inactivated “Dead” Whole-agent
• Killed by formalin or phenol
• Immunity not life-long
– Boosters may be required
– Primarily humoral response
• Examples:
– Viral: Salk (polio, IPV), Rabies, Flu
– Bacterial: Pneumococcal, Cholera

36. Subunit Vaccines
• Highly immunogenic fragments
– Cannot replicate in host
– Less side-effects/ dangers
• Recombinant vaccines
– Desired Ag fragment expressed by unrelated, non-pathogenic microbe
– Ex. HepB virion protein in GM yeast
– Rabies glycoprotein in Vaccinia virus (V-RG)
• Toxoids
– Tetanus, diphtheria
– Several injections required for full immunity
– Boosters every 10 years
• Conjugated Vaccines
– Capsular polysaccharides: poor immunogens; T-independent Ags
– Conjugate with Toxoid for maximal immunity
– Ex. Hib

37. Nucleic Acid Vaccines (DNA vaccines)
• Newest “promising” vaccines
• Plasmid DNA
– Containing gene for immunogen of interest
– Injected intramuscularly
• Gene gun
• Conventional needle
– Expressed Protein Ag  Red Bone Marrow humoral
and cellular immunity
• Long lasting immunity
• West Nile vaccine (horses)
• Human trials underway

38. Types of Vaccine
Gene gun = DNA coated with gold or tungsten
nanoparticles are “shot” into dermal cell cytosol
• Inserted with glass micropipette
- Diameter smaller than cell
- Punctures plasma membrane
• Eliminates
• syringes/needles
• refrigeration
• lower costs

39. Recommended Immunization Schedule

40. Vaccine Development
• Whole-agent vaccine
– Grow in large amounts for use
• Early days
– Smallpox scarified onto shaved calf bellies
• Cow “junk”
– Flu, Polio: grown in Eggs
• Egg protein: allergen
– Human cells required
• First HepB vaccine used Ags from chronically
infected as source
• Tissue culture Yolk sac
Allantoic
cavity
Amniotic
cavity
Chorioallantoic
membrane

41. Current Vaccine Development
• Tissue Culture
– Tissue slice
– Digest with enzymes (trypsin)
• Breaks down tissue into single cells
– Nutritive growth media
• Cells adhere and divide to from a “monolayer”
– Infect with virus
• CPE (cytopathic effect) caused by virus infection

42. Vaccine Development
Advancement in cultivation: cell culture
Viruses may be grown in:
Primary cell lines = derived from tissue slices; die out
after a few generations
Diploid cell lines = develop from human embryos;
maintained for ~100 generations
Continuous cell lines = (aka immortal cell lines)
Cancerous cells; can be maintained indefinitely
Ex) HeLa cell line
• tend to have:
- Less round shape
- Chromosomal abnormalities

43. Vaccine Safety: Risks v/s benefits
• Disease caused by vaccine
– Smallpox
• Variolation
– Incidence of disease decreased from 25% to 1%
– OPV (Sabin)
• Poliovirus mutated
• Reversion to wt
– Poliomyelitis
• Risk v/s Benefits
– Public reaction
• Low perceived risk of contracting disease
– Polio, measles
• Reports/ rumors of harmful effects
– MMR  autism
– Flu  Guillain Barre syndrome
• Herd immunity

44. Immune Disorders

45. Hypersensitivity
• Abnormal reaction to Antigen
– Allergy
– Sensitization to previous exposure to Allergen
– Higher exposure to Antigen
• Sensitized
• Immune response to low levels of Ag
– Genetic predisposition

46. Hypersensitivity
Hygiene hypothesis = sterile environments don’t provide
enough stimulation for immune system
• Higher incidence in developed
countries
• Eczema and hay fever less likely
in children from larger families
• Allergies linked to antibiotic use
in 1st year of life
• Asthma linked to use of
household antibacterials

47. Hypersensitivity Reactions
• Type I: Anaphylaxis
– Sytemic anaphylaxis (Anaphylactic shock)
– IgE response
• Type II: Cytotoxic Reactions
– IgM, IgG, complement response
• Type III: Immune complex reactions
– IgG response against soluble Antigen
• Type IV: Delayed Hypersensitivity Reaction
– Cell mediated response (CTL or ADCC)

48. Type I: Anaphylactic Reactions
• Rapid
– 2-30 mins after exposure
– Systemic
• Shock, breathlessness, can be fatal
– Localized
• Hives
• IgE response
– Binds basophils/ mast cells
– Degranulation: release mediators
• Histamine
• Leukotrienes
• Prostaglandins
– Swelling, inflammation, runny nose, contraction of smooth
muscles

49. Anaphylactic Reactions
Mediators: attract neutrophils and eosinophils to site of
degranulated cell; and:
Histamine
• Increase vessel permeability
Swelling, redness
• Smooth muscle contraction
Breathing difficulty
Leukotrienes & Prostaglandins
• Not preformed in granules
• Leukotrienes: prolonged smooth muscle contraction
asthmatic bronchial spasms
• Prostaglandins: vasodilation, fever, pain

50. Systemic & Localized Anaphylaxis
• Systemic
– Shock
– Second or subsequent exposure to allergen
• Mediators  vasodilation  BP drop (shock)
• Injected antigens (insect bites)
– Epinephrine
• Constricts blood vessels
• Localized
– Ingested or inhaled allergen
• Pollen
– Inhalation
• Itchy eyes, runny nose, congestion, coughing, sneezing
– Antihistamine (blocks histamine receptors)
– Ingestion
• Food allergies
• Hives, systemic anaphylaxis

51. Systemic & Localized Anaphylaxis
SEM of pollen grains, dust mite
• common inhaled triggers of localized anaphylaxis
Ingestion: 8 foods = 97% food allergies
• Eggs, peanuts, tree nuts, milk, soy, fish, wheat, peas
- 200 food allergy deaths per year in U.S.

52. Type II:Cytotoxic Reactions
• complement activation by IgG/ IgM with an
antigenic cell
Ex) Transfusion reactions
• RBCs destroyed by circulating antibodies

53. Type III: Immune Complex Reactions
• IgG/ IgM against soluble antigens circulating in serum
Immune complexes:
• [Ag] > [Ab]
• Complexes evade phagocytes
• Soluble, circulating
• “stuck” on capillaries, joints, organ tissues
• Activate complement:
 Transient Inflammation
 Attract neutrophils  enzymes
- tissue destruction
Glumerulonephritis = inflammatory
damage to kidney glomeruli

54. Type IV: Delayed Cell-Mediated
Reactions
• T-cell activation
• Development time: longer
– Days
– T-cell and macrophage migration/ accumulation
• Sensitization
– Macrophage phagocytoses Ag
– Presents to T-cells
– T-memory cells formed
• Subsequent exposure
– Memory cells activated
– Cytokines releases
• Attract and activate macrophages

55. Delayed Cell-Mediated Reactions
Ex) Allergic contact dermatitis =
exposure to substances to which you
have become extra sensitive
• Fragrances
• Metals
• Plant oils (poison ivy)
• Latex
Graft rejection Poison ivy plant
Catechols = oils secreted by poison ivy plant
• Combine with skin proteins, become antigenic 
immune response
• First contact: sensitization
• Second exposure: contact dermatitis

56. Comparison of the four types of
hypersensitivity

57. Autoimmune Diseases
• Hosts immune response against self
– Loss of discrimination between self v/s non-self
– Thymic selection
– >40 known ds., 75% women
• Autoimmune hepatitis
– Hepatocytes display MHC-II to APCs
• Viral infections (HepC, EBV)
• Medications
• Genetic predisposition

58. Autoimmune Diseases
• Immune complex reactions
– Rheumatoid arthritis
• Immune complexes (IgG/ IgM) deposits in joint
• Chronic inflammation
• Damage to bone/ joint cartilage
– SLE (systemic lupus erythematosus)
• Abs against cell components
– DNA
– Tissue breakdown
• Cytotoxic autoimmune reactions
– Graves Disease
• Abs that mimic TSH bind TSH-receptors
• Increased production of thyroid hormones
– Hyperthyroidism
– Goiter, bulging eyes

59. Immunodeficiencies
• Absence/ deficient immune response
• Congenital
– DiGeorge’s syndrome (22q11.2)
• Chromosome 22
• Defective/ missing thymus
– No CMI
– Frequent/ severe infections
• Acquired: drugs, cancer, infectious agents
– AIDS
• Final stage of HIV
• Destruction of T-helper (CD4+) cells
– cancer, bacterial, viral, fungal, and protozoan diseases
» Pneumocystis pneumonia, Kaposi’s sarcoma
• Diagnosis: CD4+ T-cell count below 200 cells/μl
• Chemotherapy: inhibit viral enzymes
reverse transcriptase inhibitors

60. Types of Acquired Immunity:
Active & Passive Immunity
Active immunity = acquired from an immune response to
exposure of foreign antigens
• Naturally acquired = exposure to antigens leads to
illness, recovery
• Artificially acquired = vaccination
Passive immunity = acquired from transfer of antibodies
from one person to another
• Naturally acquired = mother to infant
- Transplacental, breast milk
• Artificially acquired = injection of antibodies