Introduction to IMMUNOLOGYGeneral Concepts

Let's get familiar with themRead DIR-page 1-18

Where is your immune system?

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Where is your immune system?

Immune System lies in your blood...and somewhere else

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...and somewhere else

the average human has 5 litres of blood

it is a transporting fluid

it carries vital

Blood

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it carries vital

substances to all parts of the body

X 500

Plasma (55%): liquid part of blood. Plasma transports:-Soluble food moleculesWaste productsHormones Antibodies

Red blood cells (5-6 millions /ml): transport oxygen, specialised to do thisAlso carry some CO2

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White blood cells (5000 /ml)

Platelets (150,000 to 400,000 per mm3):

if you get cut, platelets produce tiny fibrin threads these form a web-like mesh that traps blood cells.Theseharden forming a clot, or "scab.

x 1000

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COMPLETE BLOOD COUNT WITH DIFFERENTIAL (CBC WITH DIFF)

References Ranges

Erythrocytes (RBC) 4.0 to 5.4 M/uLThrombocytes (Platelets) 145 to 400 K/uLLeukocytes (WBC) 4.8 to 10.8 K/uL

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Neutrophils 40 to 74 % Band neutrophils 0 to 9 Eosinophils 0 to 6Basophils 0 to 1 Lymphocytes 15 to 47 Monocytes 0 to 12

ORIGIN OF CELLS OF THE IMMUNE SYSTEM

Derived from common progenitor cell in bone marrow Pluripotent hematopoietic stem cell

Progenitor Stem Cells1. Erythroid lineage

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1. Erythroid lineage Erythrocytes and Megakaryocytes

2. Myeloid lineage Monocyte/ macrophage, dendritic cells, PMNs, mast cells

3. Lymphoid lineage Small and large lymphocytes

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CELLS OF INNATE AND ADAPTIVE IMMUNITY2. Myeloid Lineage

Neutrophil Principal phagocytic cell of innate immunity

Eosinophil Principal defender against parasites

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Basophil Functions similar to eosinophils and mast cells

Referred to as Polymorphonuclear leukocytes (PMNs)

Nuclei are multilobed (2 to 5) Granulocytes

Cytoplasmic granules

Diagram

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Real Image

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CELLS OF INNATE AND ADAPTIVE IMMUNITY

2. Myeloid lineage Monocytes

Leukocytes with bean shaped or brain-like convoluted nuclei

Circulate in blood with half life of 8 hours

Precursors of tissue macrophages

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Precursors of tissue macrophages

Macrophages Mononuclear phagocytic cells in tissue

Derive from blood monocytes

Participate in innate and adaptive immunity

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The real onesCrawling Macrophage

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Neutrophil and DCs

CELLS OF INNATE AND ADAPTIVE IMMUNITY

3. Lymphoid Lineage Large lymphocytes (large granular lymphocytes)

Natural killer (NK) cells (CD16, CD56) Innate immunity to viruses and other intracellular

pathogens

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Participate in antibody-dependent cell-mediated cytotoxicity (ADCC)

Small lymphocytes B cells (CD19) T cells (CD3, CD4 or CD8) Adaptive immunity

Lymphocytes refers to small lymphocytes

Now, you know how to discriminate the cells of myeloid lineageBut

How to distinguish the cells of lymphoid lineage?

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lymphoid lineage?

THE CLUSTER OF DIFFERENTIATION (CD) A protocol for identification and investigation of cell

surface molecules

CD number assigned on basis of 1 cell surface molecule recognized by 2 specific monoclonal antibodies

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recognized by 2 specific monoclonal antibodies

CD nomenclature established in 1982 1st International Workshop and Conference on Human

Leukocyte Differentiation Antigens (HLDA)

THE CLUSTER OF DIFFERENTIATION (CD) CD markers on leukocytes (WBC, all types)

Granulocyte CD45+, CD15+Monocyte CD45+, CD14+T lymphocyte CD45+, CD3+T helper lymphocyte CD45+, CD3+, CD4+

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T helper lymphocyte CD45+, CD3+, CD4+T cytotoxic lymphocyte CD45+, CD3+, CD8+B lymphocyte CD45+, CD19+Natural killer cell CD45+, CD16+, CD56+, CD3-

The immune system

Immune system

Anatomic barriers (Skin,mucous

membranes)Antigen specificity

Innate (non-specific) immunity Adaptive (specific) immunity

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membranes)

Physological barriers (temperature,

pH)

Phagocytic Barriers (cells that eat

invaders)

Inflammatory barriers (redness,

swelling, heat and pain)

Diversity

Immunological memory

Self/nonself recognition

Types Of Immunity1. Inborn or innate immunity: It is present at birth; This is our

First Line Of Defense.

2. Acquired or specific: It is not present at birth but becomes part of our immune system as the lymphoid system develops.

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develops.

1970: WHO defined immunity as immune response to antigen ( Foreign body) in form of

1. Humoral ( activation of B-lymhocytes)2. Cellular (by activation of T-lymphocytes)

Our immune systems generate an almost infinite variety of cells and substances

Foreign Recognition

Effector Response Memory

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Effector Response MemoryTo eliminate or neutralize particle Upon 2 exposure produces enhanced response

*Problems of the Immune System:

In some cases, the IR fails to function; at other times, the IR can turn on its host

Humoral and cellular immunity(antibody mediated or cellular)

AFC

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Discussion Topics1. Why do warm-blooded, long-lived animals require

particularly complex immune defense?- p4-DIR

2. Why would removal of Ag lead to the decline in an immune response?- p14-DIR

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immune response?- p14-DIR

3. Lets go to Critical Thinking, p18-DIR. Rewrite our discussion as a homework.

And many more to explore in the DIR textbook

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THE INNATE IMMUNE RESPONSE Mediated (initiated) by phagocytes, NK cells and soluble proteins Phagocytes

Cells specialized in the process of phagocytosis Macrophages

Reside in tissues and recruit neutrophils

Neutrophils

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Neutrophils Enter infected tissues in large numbers

Recognize common molecules of bacterial cell surface using a few surface receptors

Phagocytosis Capture, engulfment and breakdown of bacterial pathogen

Something to understand more about phagocytosis and its followed consequences

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THE INNATE IMMUNE RESPONSE Inflammatory response enhances phagocytosis through acute phase

proteins Mannose-binding lectin (MBL)

Binds to bacterial surface with particular spatial arrangement of mannose or fucose

C-reactive protein (CRP) Binds to phosphorylcholine on bacterial surface

Complement: More info comes up in the next lecture

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Complement: More info comes up in the next lecture Set of proteins which bind to bacterial surface

Inflammatory response Accumulation of fluid and cells at infection site (swelling, redness, heat

and pain)

an overview on Inflammation

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THE ADAPTIVE IMMUNE RESPONSE Creates millions of different B and T cells for specific antibody-mediated

and cell-mediated immunity

Antibody-Mediated Immunity (AMI) Involves B lymphocytes, plasma cells and antibodies Humoral immunity

Name derives from antibodies found in body fluids (humors - old

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Name derives from antibodies found in body fluids (humors - old medical term)

Cell-Mediated Immunity (CMI) Involves T lymphocytes, antigen-presenting cells and MHC (major

histocompatibility complex) molecules Cellular immunity

ANTIBODY-MEDIATED (HUMORAL) IMMUNITY Directed against extracellular microorganisms

and toxins

B-lymphocytes (B cells) Differentiate into plasma cells which produce antibodies

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Differentiate into plasma cells which produce antibodies Function as antigen-presenting cells (APCs)

Classification of Antibodies (Immunoglobulins) Immunoglobulin M (IgM) Immunoglobulin G (IgG) Immunoglobulin A (IgA) Immunoglobulin D (IgD) Immunoglobulin E (IgE)

CELL-MEDIATED IMMUNITY (CMI) Directed against intracellular microorganisms

Non-phagocytic cells and phagocytic cells

T-lymphocytes (T cells) Differentiate into effector cells following antigen presentation by

antigen presenting cells (APCs)

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Functional types of T cells Helper (CD4 T cells)

TH1 and TH2 cells Cytotoxic (CD8 T cells) Regulatory

CD4 and CD8 Tregs

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THE NATURE OF ANTIGENS Historically named as antibody generators

Molecule which stimulates production of and binds specifically to an antibody

Contemporary view distinguishes between Antigen

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Molecule which can bind to specific antibody but cannot elicit adaptive immune response

Immunogen Molecule which can stimulate adaptive immune response

Best immunogens are proteins with MW > 10,000

THE NATURE OF ANTIGENS Carbohydrates, nucleic acids and lipids are also potential antigens

/ immunogens Hapten

Small (low MW) molecule unable to elicit immune response Combines with larger carrier molecule which together function as

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immunogen Antibody may react independently with hapten following

hapten/carrier adaptive immune response Example

Penicillin G (MW of 372) Albumin (MW of 66,000)

THE NATURE OF ANTIBODIES Antibodies are glycoproteins

Exist as monomers, dimers or pentamers of basic structure

Basic antibody structure has 4 polypeptide chains 2 identical light chains

2 identical heavy chains

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2 identical heavy chains

Regions of heavy and light chains Variable

Constant

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THE NATURE OF ANTIBODIES Also referred to as

Immune globulins / Immunoglobulins (IG) Immune serum globulins (ISG) Gamma globulins

Contemporary immunology

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Contemporary immunology Antibody

Secreted form of IG made by plasma cells

Immunoglobulin Antigen binding molecules of B cells

(B cell antigen receptors)

CLASSIFICATION OF ANTIBODIES (IMMUNOGLOBULINS)

Five (5) classes (isotypes) Immunoglobulin A (IgA) Immunoglobulin G (IgG) Immunoglobulin M (IgM) Immunoglobulin D (IgD)

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Immunoglobulin D (IgD) Immunoglobulin E (IgE)

Based on structural differences in constant regions of heavy chains

Classes have specialized effector functions

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B LYMPHOCYTES AND HUMORAL IMMUNITY

Originate from stem cells in bone marrow

Maturation in bone marrow followed by migration to secondary lymphoid tissue

Antigen exposure in secondary lymphoid tissue

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Following exposure to antigen, differentiation into plasma cells and memory cells

Plasma cells produce antibodies of all IG classes

ACTIVATION OF ANTIBODY PRODUCING CELLS BY CLONAL SELECTION

B lymphocytes recognize intact pathogenic microorganisms and toxins

B lymphocytes possess specific surface receptors for recognition of specific antigen IgM and IgD

Binding of specific antigen results in proliferation of a clonal population of cells

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cells

Antigen determines clonal proliferation

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ACTIVATION OF ANTIBODY PROCDUCING CELLS BY CLONAL SELECTION

Proliferation of activated cells is followed by differentiation into Plasma cells

Life span of 4 to 5 days 1 to 2 months

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Produce 2,000 antibody molecules / second Memory cells

Life span of years to decades Differentiate into plasma cells following stimulation by same

antigen

PRIMARY AND SECONDARY ANTIBODY RESPONSE

Primary Response

Following exposure to an antigen, there is a slow rise in IgM followed by a slow rise in IgG

Secondary Response

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Secondary Response

Following exposure to previously encountered antigen, there is a rapid rise in IgG and slow or no rise in IgM

Memory or anamnestic response

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T LYMPHOCYTES AND CELL-MEDIATED IMMUNITY

Originate from stem cells in bone marrow followed by migration to thymus gland

Maturation takes place in thymus gland followed by migration to secondary lymphoid tissue

Respond to antigens on the surface of antigen presenting cells

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Respond to antigens on the surface of antigen presenting cells (APCs)

Antigen presenting cells (APCs) Macrophages Dendritic cells B lymphocytes

T LYMPHOCYTES AND CELL-MEDIATED IMMUNITY

Antigen presenting cells (APCs) Ingest and process antigens then display fragments (short peptides) on

their surface in association with molecules of major histocompatibility complex (MHC)

Major histocompatibility (MHC) molecules

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MHC class I molecules Present antigens to CD8 T cells

MHC class II molecules Present antigens to CD4 T cells

T cells which encounter antigen differentiate into effector T cells

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ROLES OF EFFECTOR T CELLS IN IMMUNE RESPONSE

CD8 cytotoxic T cells Enter bloodstream and travel to infection site Kill cells infected with viruses and other intracellular

microorganisms

CD4 TH1 helper T cells

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CD4 TH1 helper T cells Enter blood stream and travel to infection site Help activate macrophages

CD4 TH2 helper T cells Work within secondary lymphoid tissues Help activate B cells

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DISORDERS OF THE IMMUNE SYSTEM Hypersensitivity Reactions

Over-reaction of adaptive immune response to harmless antigens

Four Types of reactions (I- IV) Autoimmunity

Misdirected adaptive immune response

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Misdirected adaptive immune response Results from a loss of self-tolerance Three Types (II, III, IV) of reactions

Immunodeficiencies Components of immune system either absent or

defective Genetic or acquired etiology

IMMUNOLOGY FOR DIAGNOSIS OF DISEASES

Analytical methods using either antibody or antigen with an indicator system for detecting specific Antibodies

Detected using antigens or antibody Antigens

Detected using antibody

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Detected using antibody

Indicator systems Latex particles (colored) Microspheres (colored) conjugated with antibody Enzymes conjugated to antibody Fluorochromes conjugated to antibody Nitrocellulose membranes fixed with antigen or antibody

METHODS IN DIAGNOSTIC IMMUNOLOGY

Latex agglutination (LA) Latex particles (dyed) coated with antigen, antibody or? Read visually for clumping of latex particles

Staphyloslide (Becton Dickinson) Identification of Staphylococcus aureus

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Identification of Staphylococcus aureus Staphylococcus aureus produces

Coagulase (bound and free) Protein A

Blue latex particles coated and not coated with Fibrinogen IgG

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METHODS IN DIAGNOSTIC IMMUNOLOGY Immunochromatographic assay (ICA)

Antibody or antigen immobilized (Test line) Antibody immobilized (Control line) Membranes

Nitrocellulose, cellulose acetate

Read visually for colored test and control lines

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Read visually for colored test and control lines Examples

Group A Streptococcus (GAS) antigen Influenza A and B antigens Respiratory syncytial virus (RSV) antigen Rotavirus antigen HIV-1/2 antibody

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PRINCIPLES OF OraQuick RAPID HIV-1/2 ICA ANTIBODY TEST

Antigens and antibody immobilized onto nitrocellulose membrane in T and C zones

Test (T) Zone Synthetic peptides from HIV envelope region

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Control (C) Zone Goat anti-human IgG

Developer solution Facilitates flow of specimen onto test strip Rehydrates protein-A gold colorimetric reagent

IMMUNOLOGY FOR PREVENTION OF DISEASE

Hepatitis B Pre-exposure prophylaxis

Vaccination with hepatitis B surface antigen (HBsAg)

Post-exposure prophylaxis Administration of

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Administration of Hepatitis B Immune Globulin (HBIG) Human

Purified IgG antibody from plasma of donors with high titer of antibody to the hepatitis B surface antigen (anti-HBs)

IMMUNOLOGY FOR TREATMENT OF DISEASE Rheumatoid Arthritis

Remicade (Infliximab) IgG kappa monoclonal antibody against tumor

necrosis factor alpha (TNF-alpha)

Breast Cancer

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Breast Cancer Herceptin (Trastuzumab)

IgG kappa monoclonal antibody against human epidermal growth factor receptor 2 (HER2)