39Basic concept of Immunology

📚
IMMUNITY
▢ Introduction:
  • •
    Immunity = ability to resist foreign particles
  • •
    Foreign particles → bacteria, viruses, fungi, parasites, toxins
  • •
    Latin immunis = exempt
  • •
    Immunity = protection from infectious disease
  • •
    Immunology = study of immune system / resistance to disease
▢ Major Types:

Table 1: Major Types of Immunity

Type
Also called
Main point
Innate immunity
Non-specific immunity
General defence; first-line + rapid response
Acquired immunity
Specific / adaptive immunity
Antigen-specific; memory present
▢ On Basis of Cells:
  • •
    Antibody-mediated immunity / Humoral immunity
  • •
    Cell-mediated immunity
▢ On Basis of Alertness:
  • •
    Active immunity
  • •
    Passive immunity
📚
INNATE IMMUNITY / NON-SPECIFIC IMMUNITY
▢ Defensive Barriers:

Table 1: Innate Defensive Barriers

Barrier
Main role
Anatomic barriers
Prevent pathogen entry; first line of defence
Physiologic barriers
Temperature, pH, soluble factors
Phagocytic barriers
Phagocytosis of pathogens
Inflammatory barriers
Chemical alarm response after tissue injury / infection
▢ Anatomic Barriers:

Table 1: Anatomic Barriers

Barrier
Protective mechanism
Skin
Physical barrier to microorganism entry
Mucous membrane
Surface barrier to microorganisms
Sebaceous glands
Produce sebum
Sebum
Lactic acid + fatty acids → skin pH 3–5 → inhibits microorganisms
Mucus
Entraps foreign microorganisms
Cilia
Synchronous movement → propels microorganisms out
▢ Physiologic Barriers:

Table 1: Physiologic Barriers

Barrier
Point
Temperature
Normal body temperature may inhibit pathogen growth
Chicken body temperature
Innate immunity to anthrax
Low pH
Gastric acidity destroys / inhibits ingested microorganisms
Chemical mediators
Lysozyme, interferon, complement
▢ Chemical Mediators:

Table 1: Chemical Mediators of Innate Immunity

Mediator
Nature / Source
Function
Lysozyme
Hydrolytic enzyme in mucus + tears
Digests peptidoglycan of bacterial cell wall
Interferon
Glycoproteins from virus-infected cells
Makes nearby cells resistant to viral infection
Complement
>30 inactive serum proteins
Activated complement → membrane pores → pathogen lysis
▢ Phagocytic Barriers:
❖ Definition: Phagocytosis = ingestion of extracellular particulate material / pathogens
❖ Cells:
  • •
    Blood neutrophils
  • •
    Blood monocytes
  • •
    Tissue macrophages
▢ Inflammatory Barriers:
❖ Definition: Inflammatory response = complex sequence after wound / pathogen invasion
❖ Chemical Signals:
  • •
    Histamine
  • •
    Prostaglandins
  • •
    Kinins
❖ Source: Damaged mast cells → histamine + prostaglandins
❖ Effects:
  • •
    ↑ capillary permeability
  • •
    Fluid influx
  • •
    Oedema
❖ Histamine: Principal inflammatory mediator released after tissue injury
❖ Kinins: Small peptides normally present in blood plasma
📚
ACQUIRED IMMUNITY / SPECIFIC IMMUNITY / ADAPTIVE IMMUNITY
▢ Introduction:
  • •
    Recognizes specific microorganisms + molecules
  • •
    Eliminates specific foreign antigens
  • •
    Found only in vertebrates
  • •
    Response directed against specific antigen
▢ Characteristics:

Table 1: Characteristics of Acquired Immunity

Characteristic
Meaning
Antigenic specificity
Distinguishes subtle antigenic differences
Diversity
Recognizes billions of different antigenic structures
Immunologic memory
Second exposure → stronger / faster immune response
Self / non-self recognition
Responds to foreign antigens; avoids self-antigens
📚
CELLS OF IMMUNE SYSTEM
▢ Lymphocytes:
  • •
    B-lymphocytes / B-cells
  • •
    T-lymphocytes / T-cells
▢ Antigen Presenting Cells:
  • •
    Macrophages
  • •
    Dendritic cells
  • •
    B-cells
📚
B-LYMPHOCYTES / B-CELLS
▢ Introduction:
  • •
    Mature in bone marrow
  • •
    Each B-cell expresses unique antigen-binding receptor
  • •
    B-cell receptor = membrane-bound antibody
  • •
    Chemically glycoprotein
  • •
    Antigen binding → rapid B-cell division
  • •
    Progeny → memory B-cells + effector B-cells / plasma cells
▢ Types of B-Cells:

Table 1: B-Cell Types

Type
Feature
Function
Memory B-cells
Long lifespan
Express same membrane-bound antibody
Effector B-cells / Plasma cells
Short lifespan; no membrane-bound antibody
Secrete antibodies
▢ Plasma Cells:
  • •
    Responsible for antibody secretion
  • •
    Live only few days
  • •
    Secrete enormous antibody amount
  • •
    Single plasma cell → >2000 antibody molecules/second
  • •
    Secreted antibodies = major effector molecules of humoral immunity
📚
ANTIBODIES / IMMUNOGLOBULINS
▢ Introduction:
  • •
    Antibodies = protein molecules called immunoglobulins / Ig
  • •
    Produced by lymphocytes
  • •
    Specifically inactivate antigen
  • •
    Y-shaped molecule
  • •
    4 amino acid chains → 2 heavy chains + 2 light chains
  • •
    Chains linked by disulphide + non-covalent bonds
▢ Structure:

Table 1: Antibody Structure

Part
Meaning / Function
Heavy chains
2 long chains
Light chains
2 short chains
Fc / constant fragment
Tail portion of antibody; made by heavy chains
Fab / antigen-binding fragment
Tip of each arm; binds antigen specifically
▢ Major Classes: IgA, IgD, IgE, IgG, IgM
▢ Types of Immunoglobulins:

Table 1: Immunoglobulin Types

Ig
Structure
Key points
IgA / Secretory Ig
2 monomers + secretory piece / J chain
Second largest Ig; secreted in GI tract, respiratory tract, body surface; found in tears, saliva, colostrum
IgD
Single monomer
B-cell surface receptor site for antibody secretion
IgE
Single monomer
Major role in allergic reactions
IgG
Single monomer
Most important Ig; ≈ 80% of total Ig; crosses placenta
IgM
5 monomers
Largest Ig; second important due to huge size; cannot cross placenta; remains in bloodstream
▢ Effector Mechanisms:

Table 1: Antibody Effector Mechanisms

Mechanism
Meaning
Tagging
Antibodies do not directly destroy antigens; they tag them for destruction
Agglutination
Antibodies bind antigens → large insoluble harmless complexes
Opsonization
IgG coats antigen surface → easier phagocyte recognition + digestion
Complement-mediated cell lysis
Complement enzymes form membrane pores in invading cells → lysis
📚
ANTIGENS
▢ Nature:
  • •
    Mostly large proteins
  • •
    Mostly polysaccharides
  • •
    Rarely lipids
  • •
    Rarely nucleic acids
▢ Definition: Cell-surface molecules that induce specific antibody formation
▢ Examples:
  • •
    Parts of microorganisms
  • •
    Pollen
  • •
    Egg white
  • •
    Certain fruits + vegetables
  • •
    Chicken
  • •
    Feathers
  • •
    Blood cells from other persons / animals
  • •
    Tissues
  • •
    Organ transplants
▢ Epitopes: Antigenicity of large molecules depends on epitopes on surface
▢ Haptens:
  • •
    Non-proteinaceous substances
  • •
    Act as antigens by combining with antibody bonding site
  • •
    Do not induce antibody production alone
▢ MHC / Major Histocompatibility Complex:
  • •
    Protein cell-surface markers on plasma membrane
  • •
    Used by immune system to identify self
📚
T-LYMPHOCYTES / T-CELLS
▢ Introduction:
  • •
    Originate from stem cells in bone marrow
  • •
    Migrate to thymus for maturation
  • •
    Mature T-cell expresses unique T-cell receptor
  • •
    T-cell receptor recognizes antigen only when bound to MHC
  • •
    Removal of thymus in newborn → failure to produce T-lymphocytes
  • •
    Transplant rejection → T-cell activity
  • •
    Responsible for cellular immunity
  • •
    T-cell membrane receptor recognizes one particular antigen
▢ Activation: Antigen recognition → multiplication + differentiation
▢ Types:

Table 1: Types of T-Cells

Type
Function
Cytotoxic / Killer T-cells
Secrete perforins → holes in attacked cell membrane
Helper T-cells
Most numerous; help immune functions; stimulate B-cells + other T-cells
Suppressor T-cells
Reduce activity of B-cells + T-cells; immune tolerance
▢ Helper T-Cells:
  • •
    ≈ 75% of T-cells
  • •
    Destroyed / inactivated by AIDS virus
  • •
    Stimulate B-cells → antibody production
  • •
    Facilitate action of other T-cells
  • •
    Some secrete lymphokines
▢ Lymphokines Secreted by Helper T-Cells:
  • •
    Interleukin 2, 3, 4, 5, 6
  • •
    Granulocyte-monocyte colony-stimulating factor
  • •
    Interferon
▢ Suppressor T-Cells:
  • •
    Make B-cells + other T-cells less active
  • •
    Protect body's own cells from immune attack
  • •
    Cause immune tolerance
  • •
    Helper + suppressor T-cells = regulator T-cells
  • •
    Some suppressor T-cells become memory cells
  • •
    Memory cells stored in spleen + lymph nodes
📚
INTERFERONS
▢ Discovery: Alick Isaacs + Jean Lindermann, 1957
▢ Nature:
  • •
    Antiviral proteins
  • •
    Produced by animal cells after viral stimulation
  • •
    Small proteins
  • •
    Molecular weight → 15,000–30,000
  • •
    Stable at low pH
  • •
    Fairly heat-resistant
▢ Types in Humans:

Table 1: Human Interferons

Type
Produced by
Alpha interferon / α-INF
Leucocytes
Beta interferon / β-INF
Fibroblasts
Gamma interferon / γ-INF
Lymphocytes
▢ Mechanism:
  • •
    Cannot stop viral replication in already infected cell
  • •
    Released to adjacent cells
  • •
    Stimulates antiviral protein / AVP production
  • •
    AVPs block viral protein synthesis
  • •
    Interfere with viral multiplication
▢ Production: Produced by genetic engineering techniques
📚
PROCESSES RELATED TO IMMUNITY
▢ Inflammation:
❖ Definition: Tissue damage triggers defensive response
❖ Symptoms:
  • •
    Redness
  • •
    Pain
  • •
    Heat
  • •
    Swelling
  • •
    Loss of function may occur
❖ Causes:
  • •
    Microbial infection
  • •
    Physical agents → heat, radiant energy, electricity, sharp objects
❖ Functions:
  1. Destroy injurious agent
  2. Limit effects by confining / walling off
  3. Repair / replace damaged tissue
❖ Pyrogen:
  • •
    Substance causing fever
  • •
    Released by WBCs
  • •
    Sets body thermostat at higher temperature
❖ Antipyretic: Aspirin → lowers fever / pyrogenic response
▢ Allergy / Hypersensitivity:
❖ Definition: Inappropriate overreaction of immune system
❖ Nature: Non-infectious, unnatural, unusual reaction to allergen
❖ Allergen: Generally weak antigen
❖ Common Allergies:
  • •
    Anaphylaxis
  • •
    Urticaria
  • •
    Hay fever
  • •
    Asthma
  • •
    Eczema
❖ Mechanism:
  1. IgE combines with antigen on mast cell surface
  2. Mast cells release histamine
  3. Histamine causes allergy symptoms
❖ Histamine Effects:
  • •
    Capillary dilation
  • •
    ↑ permeability
  • •
    Bronchial tube closure
  • •
    Mucus secretion
  • •
    Pain
  • •
    Swelling
❖ Anaphylactic Shock:
  • •
    Severe allergic reaction
  • •
    Large histamine release
  • •
    Peripheral arteries dilate
  • •
    Very low blood pressure / shock
  • •
    Fatal if not treated immediately
❖ Treatment:

Table 1: Allergy Treatment

Condition
Drug
Normal allergic reaction
Antihistamines
Anaphylactic shock
Epinephrine
📚
AUTOIMMUNE DISEASES
▢ Definition: Immune response against self-antigens → damage to own organs / tissues
▢ Cause: Loss of self-tolerance
▢ Mechanism:
  • •
    Autoantibody production
  • •
    Sensitized T-cell response against own tissue antigens
▢ Examples:

Table 1: Autoimmune Diseases

Disease
Main point
Graves' disease
Antibodies called long-acting thyroid stimulators
Myasthenia gravis
Progressive muscle weakness
Rheumatoid arthritis
IgG + IgM + complement immune complexes deposited in joints
Hashimoto's thyroiditis
Thyroid destruction mainly by T-cells
Insulin-dependent diabetes mellitus
Immune destruction of insulin-secreting pancreatic cells
Glomerulonephritis
Inflammatory damage to kidney glomeruli
📚
IMMUNE DISORDERS

Table 1: Immune Deficiency Disorders

Disorder
Defect
Thymic aplasia / DiGeorge syndrome
Defective thymus → T-cell deficiency
X-linked infantile / Bruton agammaglobulinemia
Failure to form B-cells → decreased immunoglobulins
Severe Combined Immunodeficiency Disease / SCID
Absence of both B-cells + T-cells
Chediak-Higashi disease
Phagocyte lysosomes fail to unite with microorganisms
AIDS
Acquired immunodeficiency syndrome
📚
STRENGTHENING OF IMMUNITY
▢ Vaccination:
❖ Terms:
  • •
    Vaccine + vaccination terms coined by Louis Pasteur
  • •
    Latin vacca = cow
  • •
    Vaccine = killed / inactivated / attenuated microorganisms or toxoids inducing immunity
  • •
    Vaccination = conferring immunity by vaccine administration
❖ History:
  • •
    Edward Jenner, 1796 → first vaccination against smallpox
  • •
    Louis Pasteur, 1880 → first true vaccine with weakened microorganisms against chicken cholera
❖ Toxoid:
  • •
    Inactivated exotoxin
  • •
    Induces active immunity against toxin-caused diseases
❖ Toxoid Vaccines Used Against:
  • •
    Tetanus
  • •
    Botulism
  • •
    Diphtheria
  • •
    Other diseases
❖ Attenuated Germs Used Against:
  • •
    Poliomyelitis
  • •
    Yellow fever
  • •
    Measles
  • •
    Smallpox
  • •
    Many viral diseases
❖ Types of Vaccines:

Table 1: Types of Vaccines

Type
Main point
Attenuated whole-agent vaccine
Living but weakened microbes
Inactivated whole-agent vaccine
Killed microbes; usually by formalin or phenol
Toxoid
Inactivated toxin vaccine
Subunit vaccine
Only antigenic fragments that best stimulate immune response
Conjugated vaccine
Polysaccharide combined with protein
Nucleic acid / DNA vaccine
Newest type; naked DNA
📚
TRANSPLANTATION
▢ Definition: Removal of damaged / injured tissue or organ + replacement by similar donor tissue / organ
▢ Types by Donor–Recipient Relation:

Table 1: Types of Transplantation

Type
Donor–recipient relation
Example / Note
Autograft
Same person
Skin graft for burns / plastic surgery; most successful
Isograft
Genetically identical individuals
Twin brother / sister
Allograft
Same species but genetically different
Moderate success; often temporary
Xenograft
Different species
Used as physiological dressing over serious burns
▢ Corneal Graft:
  • •
    Used when visual potential good but cornea scarred / clouded
  • •
    Higher success than many other transplants
  • •
    Healthy cornea has no blood supply
  • •
    Less WBC access → less rejection
▢ Tissue Rejection:
  • •
    Immune system recognizes donor tissue proteins as foreign
  • •
    Cellular immunity initiated
  • •
    Transplanted organ may be rejected
▢ Immunosuppressive Drugs:

Table 1: Immunosuppression

Drug / Point
Function
Immunosuppressive drugs
Given to recipient to prevent rejection
Cyclosporin
Derived from fungus; prevents kidney, heart, liver transplant rejection
Cyclosporin mechanism
Inhibits Helper T-cell activity
📚
HIGH-YIELD RECALL

Table 1: Disease & Immunity One-Liners

Fact
Answer
Health definition
Physical + mental + social well-being
Biological agents
Viruses, bacteria, mycoplasma, fungi, protozoans, helminthes
Koch anthrax organism
Bacillus anthracis
Koch TB organism
Mycobacterium tuberculosis
Syphilis organism
Treponema pallidum
Leprosy organism
Mycobacterium leprae
Immunity Latin root
immunis = exempt
Immunology
Study of immune system / resistance to disease
Innate immunity
Non-specific immunity
Acquired immunity
Specific / adaptive immunity
Acquired immunity found in
Vertebrates
Skin pH by sebum
3–5
Sebum contains
Lactic acid + fatty acids
Lysozyme acts on
Peptidoglycan
Complement proteins
>30 serum proteins
Main phagocytes
Neutrophils, monocytes, macrophages
Inflammatory mediators
Histamine, prostaglandins, kinins
B-cell maturation
Bone marrow
T-cell maturation
Thymus
Humoral immunity
B-cells + antibodies
Cellular immunity
T-cells
Plasma cell secretion
>2000 antibodies/second
Antibody structure
2 heavy chains + 2 light chains
Antigen-binding fragment
Fab
Constant fragment
Fc
Secretory antibody
IgA
Most abundant Ig
IgG
Placenta-crossing Ig
IgG
Largest Ig
IgM
Allergy Ig
IgE
B-cell receptor Ig
IgD
Opsonization Ig
IgG
Cell-surface self marker
MHC
Hole-forming protein
Perforin
Most numerous T-cell
Helper T-cell
AIDS virus affects
Helper T-cells
Regulator T-cells
Helper + suppressor T-cells
Interferon discovery
Alick Isaacs + Jean Lindermann, 1957
α-interferon source
Leucocytes
β-interferon source
Fibroblasts
γ-interferon source
Lymphocytes
Inflammation signs
Redness, pain, heat, swelling
Fever-causing substance
Pyrogen
Antipyretic example
Aspirin
Allergy mediator
Histamine
Anaphylactic shock drug
Epinephrine
Normal allergy drug
Antihistamine
Graves' disease
Long-acting thyroid stimulators
Myasthenia gravis
Progressive muscle weakness
SCID
Absence of B + T cells
Vaccination term coined by
Louis Pasteur
First vaccination
Edward Jenner, 1796
First true vaccine
Louis Pasteur, 1880
Most successful graft
Autograft
Twin graft
Isograft
Same species different genetics graft
Allograft
Different species graft
Xenograft
Anti-rejection drug
Cyclosporin
Cyclosporin action
Inhibits Helper T-cells
Q1.
Immunity means ability of body to
Q2.
The Latin word immunis means
Q3.
Study of immune system is called
Q4.
Innate immunity is also called
Q5.
Acquired immunity is characterized by
Q6.
Acquired immunity is found only in
Q7.
Which is an anatomic barrier of innate immunity?
Q8.
Sebum inhibits microorganisms because it contains
Q9.
Skin pH due to sebum is approximately
Q10.
Mucus protects by
Q11.
Cilia of mucous membrane help by
Q12.
Chicken shows innate immunity to anthrax mainly due to
Q13.
Lysozyme is found in
Q14.
Lysozyme digests
Q15.
Interferons are mainly produced by
Q16.
Complement system consists of
Q17.
Activated complement destroys pathogens mainly by
Q18.
Main phagocytic cells include
Q19.
Inflammatory response is triggered after
Q20.
Principal inflammatory mediator released after tissue injury is
Q21.
Histamine increases
Q22.
Which of the following is a characteristic of acquired immunity?
Q23.
Immunologic memory means
Q24.
B-lymphocytes mature in
Q25.
T-lymphocytes mature in
Q26.
Antigen presenting cells include
Q27.
B-cell receptor is chemically a
Q28.
After antigen binding, B-cell progeny form
Q29.
Plasma cells mainly secrete
Q30.
A single plasma cell can secrete more than how many antibody molecules per second?
Q31.
Antibodies are also called
Q32.
Basic antibody structure contains
Q33.
Antigen-binding region of antibody is called
Q34.
The tail portion of antibody formed by heavy chains is
Q35.
Secretory immunoglobulin is
Q36.
Which immunoglobulin crosses placenta?
Q37.
Largest immunoglobulin is
Q38.
Which immunoglobulin is mainly involved in allergic reactions?
Q39.
Which immunoglobulin acts as B-cell surface receptor site for antibody secretion?
Q40.
Opsonization mainly means
Q41.
Agglutination by antibody means
Q42.
Antigenicity of large molecules depends on
Q43.
Haptens are
Q44.
MHC molecules help immune system to identify
Q45.
T-cell receptor recognizes antigen only when it is bound to
Q46.
Removal of thymus in newborn leads to failure of production of
Q47.
Cellular immunity is mainly due to
Q48.
Humoral immunity is mainly due to
Q49.
Cytotoxic T-cells destroy target cells by secreting
Q50.
Most numerous T-cells are
Q51.
AIDS virus mainly destroys
Q52.
Helper T-cells stimulate
Q53.
Helper and suppressor T-cells together are called
Q54.
Memory cells are stored mainly in
Q55.
Interferons were discovered by
Q56.
Alpha interferon is produced by
Q57.
Beta interferon is produced by
Q58.
Gamma interferon is produced by
Q59.
Interferons protect nearby cells by stimulating production of
Q60.
Substance causing fever is called
Q61.
Which of the following is an antipyretic example?
Q62.
Allergy is mainly
Q63.
Allergen is generally a
Q64.
In allergy, IgE binds antigen on
Q65.
Normal allergic reactions are treated by
Q66.
Anaphylactic shock is treated immediately with
Q67.
Autoimmune disease occurs due to
Q68.
Graves' disease involves
Q69.
Myasthenia gravis is characterized by
Q70.
Rheumatoid arthritis involves deposition of immune complexes in
Q71.
Hashimoto's thyroiditis causes destruction mainly by
Q72.
Insulin-dependent diabetes mellitus may result from immune destruction of
Q73.
DiGeorge syndrome is due to
Q74.
Bruton agammaglobulinemia is due to
Q75.
SCID is characterized by
Q76.
Chediak-Higashi disease involves failure of
Q77.
The terms vaccine and vaccination were coined by
Q78.
First vaccination against smallpox was done by
Q79.
First true vaccine with weakened microorganisms was produced by Pasteur against
Q80.
Toxoid is
Q81.
Toxoid vaccines are used against
Q82.
Attenuated whole-agent vaccine contains
Q83.
Inactivated whole-agent vaccine contains
Q84.
Newest type of vaccine mentioned is
Q85.
Transplantation means
Q86.
Autograft is transplantation from
Q87.
Isograft occurs between
Q88.
Allograft is transplantation between
Q89.
Xenograft is transplantation between
Q90.
Corneal graft has high success because healthy cornea
Q91.
Tissue rejection is mainly initiated by
Q92.
Cyclosporin is used to
Q93.
Cyclosporin acts mainly by inhibiting