Prof M.I.N. Matee

Office: Microbiology and Immunology Room 19Phone: 0713-081162Email: mmatee@muchs.ac.tz

Introduction to Immunology

Immunology stems from L.- immunis = “exempt;” Eng. = protection from disease

*Protective adaptations in higher organisms to rid the body of foreign particles (microbial and otherwise) and abnormal cellsOur Immune system involves the interplay between

our Non-specific and our Specific Immune responses

Non-specific immunities collectively referred to as our Innate immunitySpecific immunities are referred to as our Adaptive immunity

towards modern times…

1718- Lady Montague became aware of a practice, called variolation or inoculation, and introduced it to Britain after first having her own children treated.

1798 –Edward Jenner noticed immunity bestowed to milkmaids – injected fluid from cowpox blister into skin of patient (orphan or prisoner)

1989- WHO announced smallpox was eradicated from the world

Lady Mary Wortley Montague (1689-1762)

War on smallpox…

Louie Louie…

1879- discovered that old bacterial cultures of Pasteurella lost virulence. Referred to injection of weakened culture a “vaccine” in honor of Jenner

1881- He applied the same technique vs. anthrax

….and then rabies

Pasteur inoculating sheep at Msr. Rossignol’s farm – May, 1881

Louis Pasteur

First insights into mechanics of immunity…

1880’s- Metchnikoff discovered phagocytic cells that ingest microbes and particles

∴cells conferred immunity

1890- von Behring and Kitasato discovered blood sera could transfer immunity

∴ liquid of blood conferred immunity

Q: Which confers immunity… cells or serum?

Emil von Behring

S. Kitasato

Elie Metchnikoff

1930’s – early techniques made it easier to study humoral elements [than cellular ones].-discovery of active component of blood –

gamma globulin “protein”

1950’s – discovery of T and B cellsLater discoveries linked lymphocytes to

both cellular and humoral immunity

A: Both cells and serum contribute to immunity!

Understanding specificity of antibody for antigen took years

Early 1900’s- Landsteiner revealed antibody could be produced vs. most any organic compound

Last 20 yrs- Antibody specificity reveals unlimited range of reactivity – also to newly synthesized chemicals!

Karl Landsteiner

Innate Immunity

Cells of the Immune System

Immune System

Myeloid Cells Lymphoid Cells

Granulocytic Monocytic T cells B cells

NeutrophilsBasophils

Eosinophils

MacrophagesKupffer cells

Dendritic cells

Helper cellsSuppressor cellsCytotoxic cells

Plasma cells

NK cells

Innate immunity is the immunity that is immediately available without having to adapt to the specific pathogen that is present.

It is not specific to a particular organism such that identical responses can protect against several organisms.

Innate immunity is mediated by phagocytes (cell that ingest bacteria or other particulate matter) such as macrophages and neutrophils. It is also mediated by chemical compounds and physical barriers that will be described later.

Three Lines of Defense Against Infection

Innate Immunity Adaptive Immunity

Comparison of Innate and Adaptive Immunity

• No memory

• No time lag

• Not antigen specific

• A lag period

• Antigen specific

• Development

of memory

Defensins (epithelium)

Figure 8.6

Progression of Immunity

At least three cell types reside within or beneath the epithelium and induce inflammation in response to trauma or microbial products: Macrophages, Mast Cells, and Langerhan’s cells (a skin dendritic cell)

Figure 8.5

Anatomical Barriers - Mechanical Factors

Flushing action of tears, saliva, mucus, urine

Epithelium (e.g. nasopharynx)

Mucociliary elevator

Ciliated epithelium (e.g. respiratory tract)

PeristalsisNon-ciliated epithelium (e.g. GI tract)

Mucous Membranes

Physical barrierDesquamation

Squamous epitheliumSkin

MechanismCell typeSystem or Organ

Anatomical Barriers - Chemical Factors

OpsoninSurfactants (lung)

AntimicrobialDefensins (respiratory & GI tract)

Low pHLysozyme and phospholipase A

HCl (parietal cells)Tears and saliva

Mucous Membranes

Anti-microbial fatty acids

SweatSkin

MechanismComponentSystem or Organ

Anatomical Barriers - Chemical Factors

OpsoninSufactants (lung)

AntimicrobialDefensins (respiratory & GI tract)

Low pH

Lysozyme and phospholipase A

HCl (parietal cells)

Tears and saliva

Mucous Membranes

Anti-microbial fatty acids

SweatSkin

MechanismComponentSystem or Organ

Anatomical Barriers - Biological Factors

Antimicrobial substancesCompetition for nutrients and colonization

Normal floraSkin and mucous membranes

MechanismComponentSystem or Organ

Humoral Components

Compete with bacteria for ironLactoferrin and transferrin

Increase vascular permeabilityRecruitment of phagocytic cellsΒ-lysin from platelets – a cationic detergent

Coagulation system

Lysis of bacteria and some virusesOpsoninIncrease in vascular permeabilityRecruitment and activation of phagocytic cells

Complement

Various effectsCytokines

Breaks down bacterial cell wallsLysozyme

MechanismComponent

Cellular Components

Killing of virus-infected and altered self targetsNK and LAK cells

Killing of certain parasitesEosinophils

Phagocytosis and intracellular killingExtracellular killing of infected or altered self targetsTissue repairAntigen presentation for specific immune response

Macrophages

Phagocytosis and intracellular killingInflammation and tissue damage

Neutrophils

FunctionsCell

• Characteristic nucleus, cytoplasm

• Granules

• CD 66 membrane marker

Phagocytes - Neutrophils (PNMs)

primary granules

contain cationic proteins, lysozyme, defensins, elastase and myeloperoxidase

secondary granules

contain lysozyme, NADPH oxidase components, lactoferrin and B12-binding protein

azurophilic; characteristic of young neutrophils;

specific for mature neutrophils

Characteristics of Neutrophil Granules

Receptors on Macrophages:

LPS receptor-CD14

Toll-like receptors

Fc receptors

Mannose receptor

Complement receptors

IFNγ receptor

Chemokine receptors

Figure 1.13Macrophages phagocytose and degrade foreign particles,bacteria and dead (and dying) host cells.

Attachment via Receptors:

IgG FcR

ScavengerR

Complement R

Toll-like R

Initiation of Phagocytosis

Phagocytosis

• Attachment

•Pseudopod extension

•Phagosome formation

•Granule fusion

•Phagolysosome formation

Toxic compounds – Superoxide anion (O2 -), Hydrogen peroxide (H2O2), Singlet oxygen (1O2) and Hydroxyl radical (OH*)

Respiratory Burst

Oxygen-Dependent Myeloperoxidase-Independent Reactions

Pentose-P + NADPHG-6-P-dehydrogenase

Glucose +NADP+

NADPH oxidaseCytochrome b558

NADP++ O2

-NADPH + O2

Superoxide dismutase H2O2 + 1O22O2

- + 2H+

2O2

- + H2O2

OH* + OH- + 1O2

Respiratory Burst

Oxygen-Dependent Myeloperoxidase-Dependent Reactions

myeloperoxidaseOCl- + H2OH2O2 + Cl-

2OCl- + H2O1O2 + Cl-+ H2O

Toxic compounds – Hypochlorous acid (OCl-), and Singlet oxygen (1O2)

Respiratory Burst

Detoxification Reactions

H2O2 + O2

Superoxide dismutase

H2O + O2

Catalase

2O2

- + 2H+

2 H2O2

Effector Molecule Function

Oxygen-Independent Killing in the Phagolysosome

Cationic proteins (cathepsin) Damage to microbial membranes

Lysozyme Hydrolyses mucopeptides in the cell wall

Lactoferrin Deprives pathogens of iron

Hydrolytic enzymes (proteases) Digests killed organisms

Summary of Intracellular Killing Pathways

Intracellular Killing

OxygenDependent

OxygenIndependent

MyleoperoxidaseDependent

MyleoperoxidaseIndependent

Nitric Oxide Dependent KillingIFNγ

γ

TNF

TNF

Nitric OxideNitric Oxide

Non-specific Killer Cells

NK and LAK cells

ADCC (K) cell

Activated macrophages

Eosinophils

They all kill foreign and altered self

targets

Natural Killer (NK) cells

◆ also known as large

granular lymphocytes

(LGL)

◆ kill virus-infected or

malignant cells

◆ identified by the presence

of CD56 & CD16 and

absence of CD3◆ activated by IL2 and IFN-

γ to become LAK cells

Lymphokine Activated Killer (LAK) cell

IL2

IFNIFN

IL2

kills malignant

cells

kills transformed

and malignant cells

K Cells

◆ morphologically undefined

◆ mediate ADCC

◆ have Fc receptor

◆ recognize antibody coated

targets

◆ could be NK cells (IgG),

macrophages (IgG),

eosinophils (IgE) or other

cells (IgG)

Cells, tissues and organs I. Cells

B. mononuclear cells: monocytes, macrophages monocytes – in blood macrophages – larger, more organelles

receptors for antibody and complementtwo populations – fixed and wandering

Cells, tissues and organs I. Cells

C. granulocytes PMN irregular nucleus, 2-5 lobes many granules, differ in staining properties 1. basophils – granules stain with basic dyes

two-lobed nucleusnon-phagocyticsecrete vasoactive agents (histamine, serotonin, prostaglandin)affinity for IgE – coats surface of the cell triggers cell to secrete vasoactive agents hayfever, asthma, exzema

Cells, tissues and organs I. Cells

C. granulocytes PMN 2. eosinophils – granules stain with acidic dyes

two-lobed nucleus, connected by thin strandmigrate to tissuesdefend against protozoa and helminths release cationic proteins & oxygen metabolites damage parasite’s membrane

3. neutrophils – granules stain at neutral pH3-5 lobed nucleusreceptors for antibody & complementmigrate to site of tissue damage/infectionmajor phagocytes many hydrolytic enzymes – digestion O2-dependent & O2-independent paths

Cells, tissues and organs I. Cells

C. granulocytes PMN 4. mast cells

in connective tissuegranules of histamine, pharmacological agentscontribute to inflammatory responseallergies and hypersensitivities

Chemical barriers (below skin & mucous membranes)fibronectin – glycoprotein binds bacteria to block attachment, enhance removalβ-lysin – cationic polypeptide from platelets disrupts Gram-positive cell’s membraneinterferon – family of glycoproteins block viral mRNA transcription enhance destruction of ‘infected cells’

intracellular parasites (Rickettsia & Chlamydia)tumor necrosis factor alpha (TNF-α) secreted by phagocytes & some T cells in response to

LPS, M. tuberculosis, etc. activates macrophages involved in inflammatory responsecomplement – later

Barriers – Chemical Chemical barriers (below skin & mucous membranes) complement – heat-labile component of blood

family of serum proteinsparticipate in immune response, specific and non-specific mediate inflammation enhance cytolysis, on antibody-coated cells activate phagocytosiscomplement cascade activation of one factor activates others

three pathwaysclassical – specific immune response (later)lectin pathwayalternative pathway

Inflammation or inflammatory response generalized response to tissue damage (scrape, bite) mediators: histamine, kinins, 5-hydroxytryptamine four signs/symptoms

erythema (rubror)edema (tumor)– IgG, complement, etc., to tissuespain (dolor) – tissue distensionwarmth (calor) – slight temperature elevation (LOCAL)

clot to wall off area

inflammatory mediators: histamine, leukotrienes,bradykinin, prostaglandin

capillary endothelium activated attract/catch neutrophils dilate to increase permeability, blood supply

Chronic inflammation

two weeks or longer duration dense infiltration by lymphocytes and macrophages

cause tissue damage granuloma forms, due to continual presence of pathogens or

large antigen-antibody compleses new connective tissue formed

Phagocytosis opsonin-dependent – mediated by antibodies or C3b

recognized by phagocytes

Phagocytosis opsonin-independent

variety of non-specific & specific receptors on phagocytes lectin – carbohydrate binding protein protein-protein binding

Cytokines immunoregulators – soluble proteins/glycoproteins

intercellular mediators, intracellular meditors

monokines – from mononuclear phagocytes lymphokines – from T lymphocytes interleukins – from leukocytes, act on other leukocytes colony-stimulating factors (CSF) – stimulate immature

leukocytes in bone marrow

Interferon family of glycoproteins

block viral mRNA transcriptionenhance destruction of ‘infected cells’ intracellular parasites (Rickettsia & Chlamydia)

Fever

elevation of body temperature

prostaglandin targets hypothalamusheat conservation mode – decrease circulation to skinheat generation mode – shivering

heat dissipation mode – increase circulation to skin sweating

aspirin inhibits prostaglandin release

Figure 8.10

**

Figure 8.14

Natural killer (NK) cells are lymphocytes the can kill host cells (e.g., virus infected cells) without making their own antigen-specific receptor (do not require ab or TCR)(innate immunity)

Once referred to as large grauular lymphocytes or LGLs

Natural killer cells (NK) large, non-phagocytic granular lymphocytes non-T, non-B lymphocytesnon-T, non-B lymphocytes lack target cell specificitylack target cell specificity 1. antibody-dependent cell-mediated cytotoxicity1. antibody-dependent cell-mediated cytotoxicity

possess FC receptor possess FC receptor 2. surface receptor-mediated cytotoxicity2. surface receptor-mediated cytotoxicity

target cells lacking MHC Itarget cells lacking MHC I

Natural Killer cells 1. antibody-dependent cell-mediated cytotoxicity1. antibody-dependent cell-mediated cytotoxicity

possess FC receptor possess FC receptor

Natural killer cells 2. surface receptor-mediated cytotoxicity 2. surface receptor-mediated cytotoxicity

target cells lacking MHC Itarget cells lacking MHC I