Transcript Specific Host Defense IMMUNOLOGY

Specific Host Defense
Mechanisms: An Introduction to
Immunology
BY
Prof. DR. Zainalabideen A. Abdulla,
DTM&H., MRCPI, Ph.D., FRCPath. (U.K.)
Learning Objectives/First Lecture
Learning Objectives/Second Lecture
Immunology
Is the scientific study of the immune system and
immune response.
• Immune system: Third line of defense/Specific
• Immune response (IR): Complex interactions
Details given below
Antigens (Ag)
Are molecules that stimulates the immune
system to produce antibodies. They are
commonly proteins (most potent antigens).
Antibodies (Ab)
Are protein molecules that are produced by the
immune system in response to antigens.
Functions of the immune system
1. Differentiate between “self” and “non-self”
(foreign) antigens
2. Destroy the non-self antigens
Arms of the immune system
1. Humoral immunity
2. Cell-mediated immunity (CMI)
N.B: “Danger-Model” is a new theory to explain
IR on the basis of damaged tissues?!
Humoral immunity (Antibody-Mediated
Immunity “AMI”)
• Antibodies (Ab): Play a major role
• Ab: Present in blood/plasma/serum, lymph,
body secretions/extracellular fluid, and on
surface of some lymphocytes (B-cells)
Cell-Mediated Immunity (CMI)
• Involve various types of cells
• Ab play ONLY a minor role
Types of acquired immunity (AI)
1. Active: Ab produced the body, long:
A. Natural: Infections; protective Ab
B. Artificial: Vaccination
Edward Jenner, Cowpox
Vacca = Cow
2. Passive: Ab “received”; short-lasting
A. Natural: Mother to fetus (IgG, IgA; 6 m )
B. Artificial: Preformed Ab to patients,
e.g. HBV exposure
Natural Passive Acquired Immunity
• IgG is the only Ab can cross the placenta
• Colostrum (Milk few days before/after delivery
Rich in secretory IgA)
Artificial Passive Acquired Immunity
• Temporary protection
• Gamma globulin (pooled immune serum
globulin “ISG”) e.g. Measles, Mumps, Polio
• Hyperimmune serum (high level) e.g. HBIG,
tetanus, rabies, botulism
Vaccine
Material that can artificially induce immunity to
infectious disease; injected or ingested.
• Produce Ab and memory cell
• Ideal Vaccine:
- Enough antigenic determinants
- Against all causative strains
- Not cause a disease
Types of vaccines
1. Living organisms (harmless or attenuated)
- Attenuated = Modified/ Weakened
- Most effective
- Some given at birth (Hepatitis A & B,
Rota, DTaP, Hib, Polio, MMR, Chickenpox, Influenza, Pneumococcal, Meningo
- Others: On need, e.g. cholera
- Antigenic variation: e.g. Influenza virus
2. Inactivated (Killed): Weaker/shorter
e.g. Hepatitis A, Rabies, Polio
cont./…
cont./… types of vaccines
3. Subunit vaccines (acellular)
- Part of a microbe , e.g. Pertussis
- Genetically produced part, e.g. HBsAg/yeast
4. Conjugate vaccine, e.g. Hib, Pneumococcal
5. Toxoid (detoxified) e.g. Diphtheria, Tetanus
6. DNA vaccines (still experimental):
Gene
Plasmid
Human
Ag/Ab
7. Autogenous vaccines:
Isolated m.o.
Killed
Injected
Ab
How vaccines work
1. Antibodies:
• Anti-Toxin, e.g. anti-tetanus toxin
• Anti-surface Ag/Pili; Prevent attachment
• Opsonization
• C activation
Lysis
2. Memory cells (lymphocytes)
Cells of the immune system
1. T lymphocytes (T cells)
2. B lymphocytes (B cells)
3. Natural Killer (NK) cells
4. Macrophages
B.M. Lymphoid Stem Cells
Lymphocytes
T- cells
1. T helper (TH ) = CD4
- TH1: Help CMI; produce type 1 cytokines
- TH2: Help B cells (Ab-production),
produce type 2 cytokines
2. T cytotoxic (Tc)- CD8
- Killer: Virally infected cells, foreign cells,
tumor cells
Location of immune response
• Ag in the blood
Spleen
• Ag in tissues
Local L.N.
• Ag via mm
Mucosal-associated
lymphoid tissues
Examples:
• Intranasal/inhaled Ag
Tonsils/Adenoids
• Ingested Ag
Microfold (M) cells
Peyer’s
patches of the intestine
Humoral Immunity
Antigens
• Antibody-generating substances are called
antigenic or immunogenic.
• Proteins (> 10,000 Da), Polysaccharides
(> 60,000 Da), or larger DNA or RNA and
combinations: glycoproteins, lipoproteins,
nucleoproteins
• Best antigen: Proteins (more immunogenic)
Antigenic determinants (AD)
Are the surface molecules that stimulate the
antibody production (> AD // > Immunogenicity)
Haptens
Are antigens that can bind antibodies, but can
not stimulate their production unless coupled to
a larger carrier molecule such as protein.
Example:
Penicillin (hapten) + Serum albumin (carrier)
Allergy (Type-I Hypersensitivity) in some individuals
T-dependent antigens
Are antigens that depend on TH-cells in their
processing (involve also macrophages & B cells)
T-independent antigen
Are antigens which require only B cells (do not
require TH-cells) in their processing
Processing: Stimulation of B-cells to become
plasma cells that produce antibodies
Immune response (IR)
1. Primary response:
• 10-14 days after Ag stimulation
• IgM mainly
• Memory cells: B and T cells
2. Secondary response (Anamnestic/Memory):
• Rapid, larger Ab quantities
• IgG mainly
• Memory cells also generated
. Booster Ag dose: Stronger
Antibodies
• Microbial Ag/AD: Capsule, cell wall, cell
membrane, pili, flagella, etc.
• Ab: - Each specific to one AD (Lock & Key)
- Cross-reacting Ab to similar Ag (AD)
• Proteins “glycoprotein” (immunoglobulin)
• Resembled = Y
Antibody structure
Monomer
• Two identical Heavy chains (H) +
Two identical Light chains (L)
• H chain heaver & more a. a. than L chain
• Chains connected by disulfide –S-S- bonds
• L chain located at the top of the Y
• The tops of both H & L are the Antigenbinding sites (Fab) - Bivalent in which a.a.
sequences are variable (VH, VL)
• The sequences of the rest: Constant (Fc)
Fc receptors
• Neutrophils, macrophages, basophils, mast
cells AND NK cells (for ADCC)
Classes of immunoglobulins
• IgA, IgD, IgE, IgG, IgM
• IgA and IgG: Subclasses
. IgG & IgM = Complement-Fixing Ab
(+ and +++ respectively); Why?
• See details in the Table
Antigen-Antibody Complexes
• Ab + Ag
= Immune complexes (IC)
• IC can activate the complement (activation
of leukocytes, lysis, opsonization)
• Acute extracellular infections: AMI
• IC
Type III Hypersensitivity
Role of antibodies in protection
I. Microbial toxin
Neutralizing anti-toxin
II. Viral adhesin
(vaccine)
Anti-adhesin prevent
attachment of virus
III. Bacterial Pili
Anti-Pili antibodies
prevent attachment
IV. Bacterial capsule
(polysaccharides)
Anti-capsule Ab
Opsonization ( phagocytosis)
Monoclonal antibodies
• Single plasma cell
Single antibody
• Tumor cells (e.g. myeloma)
Life long
• Plasma cell + Myeloma
Hybridoma
• 1 cell
divide
1 clone daughter of cells
• Applications:
- Immunodiagnostic Procedures (IDPs)
- Killing tumors
- Boost immune system
- Prevent organ rejection
- Fight diseases, e.g. autoimmune/infectious
Cell-Mediated Immunity (CMI)
• Intracellular organisms
• Cells: TH, Tc, NK, macrophages, granulocytes
• Step 1: Macrophages/phagocytosis/ APC
• Step 2: TH bind one AD on macrophages
Cytokines
Tc and NK (Effector)
• Step 3: Effector cells
bind target cell
• Step 4: Effector cells
Vesicular factors
(perforin, enzymes, TNF, NK cytotoxic factor)
• Step 5: Effector cell Toxins
DNA, Cell dies
AMI and CMI
• Viral infection (e.g., herpes infections)
• Ab & C
Neutralize & destroy virus
• CMI
Destroy virus infected cells
• Latent (e.g. Shingles)
Not destroyed
• Tc and NK cells
Killer (cytotoxic)
e.g. infected liver cells killed in viral hepatitis
• AIDS (HIV): Destroy TH cells
AMI/CMI
Susceptible to infections/malignancy
Natural Killer cells (NK cells)
• Large granular lymphocytes
• Lack B and T cell markers
• Not involved in antigen-specific recognition
• Kill: Foreign, virus-infected, tumor cells
• Have receptor for Fc region of IgG
Kill
(Antibody-Dependent Cell Mediated Cytotoxicity “ADCC”)
• How?: Perforin (pores)
Granzymes
(Cytotoxic granules inserted)
• Involve in immune surveillance system to
destroy tumor/mutated cells
Hypersensitivity
Overly sensitive or overly immune system
causing irritation or damage to cells or tissues
Types of hypersensitivity
1. Immediate Hypersensitivity (Types I, II, III)
- Antibody-mediated reactions
2. Delayed-Type Hypersensitivity (Type IV)
- Cell mediated reaction
Type I Hypersensitivity/Anaphylactic
• Allery: Hay fever, asthma, hives, food
allergy, insect stings, drug allergy,
anaphylactic shock.
• IgE antibody +
(Reagin antibody)
chemical mediators from
basophils/mast cells
• Atopic patient = Allergic patient with IgE
• Allergen = Antigen causing allergy
• Basophil/mast cells contain IgE Fc receptors
cont./… allergic reactions
• First exposure
Reagin antibody
• Second exposure
Degranulation of
basophil/mast cells
• Basophils: Anaphylaxis, Mast: Local Allergy
• Release of mediators:
Histamine, PG, serotonin, bradykinin, SRS-A,
Leukotrienes, ECF
• Allergens: e.g. Pollens, dust, fungal spores
• Anti-histamine blocks histamine binding
Systemic anaphylaxis
• Anaphylactic shock: Fatal
• Allergens: Drugs, insect venom
Example: Penicillin (hapten) + Blood protein
(carrier)
IgE
• Reaction occurs within 20 minutes (immediate)
• Treatment: Epinephrine (adrenaline) +
Anti-histamine
Latex Allergy
1. Irritant contact dermatitis
Dry, itchy, irritated hand skin, Not allergy
most common reaction to latex
2. Allergic contact dermatitis
Chemicals added to latex and poison ivy
This is DTH
3. Latex allergy
Latex, more severe, mild to severe, type-I
Allergy skin testing
• Scratch or intradermal
• Wheal and Flare (cutaneous anaphylaxis)
Hyposensitization (immunotherapy)
• Injection of small doses of allergens
• Blocking IgG antibodies; prevent attachment
of allergen to mast/basophils
• Used for: plants, insect venom, cat dander
Type II Hypersensitivity (Cytotoxic)
• IgG and IgM antibodies involved
• Complement may/may not involved
• Three mechanisms:
1. C- activation
2. Opsonization
3. NK cells (ADCC)
• Examples: ABO/Rh incompatibility
Myasthenia gravis (Anti-Ach Ab)
Drugs (bind
Anti-drug Ab
C- activation
Lysis)
Type III Hypersensitivity (IC hypersensitivity)
• IgG and IgM antibody, C, and N
• Serum Sickness: Anti-sera (e.g. horse antiClostridium botulinum toxin) “foreign”
Anti-horse Ab (IC)
Deposited in joints,
skin, kidney, Choroid plexus (brain)
• Similar in SLE, Rheumatic fever (Anti- M
protein of S. pyogenes
cross react with
cardiac muscles/valves, glomerulonephritis,
arthritis
Type IV Hypersensitivity/CMI
• DTH (24 – 48 hours or longer)
• Examples: Tuberculin (Mantoux) & fungal
skin tests, contact dermatitis, transplant
rejection, intracellular microbes
• Contact dermatitis
To metals, cosmetics, topical medication
Mantoux test
- PPT = Purified Protein Derivative used
- Steps:
1. PPD
PMN influx in 2-3 h
2. L & M; PMN disperse
3. Erythematous & edematous area 12-18 h
4. Increased intensity 24-48 h
5. Cells and manifestations disperse
Positive Mantoux (TB skin) test
• Active TB
• Past/recovered TB
• Cured TB (no live m.o.); isoniazid for 6 m
• Latent TB (no actual TB, but harbor m.o.);
isoniazid 6 m
• Bacillus Calmette-Guerin (BCG) vaccine =
attenuated strain of Mycobacterium bovis
(gives 50% protection)
N.B.: Gamma-Interferon Releasing Tests
(IGRA) are new alternatives to TB skin test
Autoimmune diseases (AID)
• Immune system reacts against self antigens
• > 80 diseases
• 1. Organ-specific: e.g. Thyrotoxicosis, DM-1
pernicious anemia, Addison’s disease
2. Organ-nonspecific: e.g. RA, SLE,
myasthenia gravis, scleroderma
• Multiple mechanisms Hypersensitivity I, II, III
• Sequestered tissues: Eye lens, brain, spinal
cord, sperms. Exposed
AID
IgM and IgG against tissues
Immunosuppression
• Immunosuppressed, immuno-depressed,
immunocompromised = Immune system
• Acquired, or inherited
• Acquired: Drugs, irradiation, HIV, aging
• Inherited: Ab production, C activity, NK/
phagocytic functions
Examples: DiGeorge syndrome (No thymus
and no parathyroid glands)
Hypo- or Agammaglobulinemia
The Immunology Laboratory
• With CML or separate
• Functions:
- Diagnosis of infectious diseases
- Immune system disorders
- Tissue compatibility for transplantation
- Immunochemical procedures
Immunodiagnostic Procedures (IDP)
• Rapid tests to detect Ag or Ab in infectious
diseases (vs culture: takes a long time)
• Serological procedures: When serum used
• Detection of Ag: Direct evidence of microbes
(Best Proof)
Detection of Ab: Indirect evidence:
- Currently infected
- Past infection
- Vaccination
- Cross reactivity (reaction)
IDPs general rules and tests
• IgM: Current infection (why?)
• Paired sera: To detect or
in Ab titer
(1st: Acute serum ; 2nd: Convalescent serum)
• Detect Ag by Ab (specific) & Vice Versa
• Tests: See Figure
- Agglutination (clumping)
- Precipitation
- Immunofluorescence (IF)
- ELISA
Antigen detection procedures
• Ab used to detect Ag
e.g. H. influenza (Ag) in CSF + Ab: Meningitis
Blood typing
• Major blood groups (ABO) & Rh factor
• Agglutination test
Antibody detection procedures
• Ag used to detect Ab
e.g. Ab (serum of patient) + Ag (bacteria): Dx
Allergy tests
• Radio-allergosorbent test (RAST) to detect
specific IgE against allergens
• Intradermal skin test to allergy to allergens
Skin testing/diagnostic tool
• Subcutaneous or intradermal tests
• Example: TB diagnosis by Mantoux skin test
Diagnosis of immunodeficiency disorders
• B, T, Phagocytic cells, Complement