Applied Immunology

Aftab Jasir: European Centre for Disease Prevention and Control (ECDC)

European Public Health Microbiology training program (EUPHEM)Introductory course, Menorca,2012

Objectives

• Define basic components of immunology

• Describe important terms in immunology • Explain major applications of immunology

What is immunology? Immunology is a broad branch of biomedical

science that covers the study of all aspects of the immune system in all living organisms.

It deals with the physiological functioning of the immune system in states of both health and disease

What is the immune system?

The immune system is the ministry of defence of the human/animal body

Immunodeficiency and Immunosuppression

Immunodeficiencyis a state in which the immune system's ability to fight infectious disease is low or entirely absent.

Immunosuppression involves an act that reduces the activation or efficacy of the immune system. immunosuppression may occur as an adverse reaction to treatment of other conditions.

Major defence components of the human immune system

Cells Immunoglobulins

Overview of the immune system

Antigens (Ag)Large molecules, is anything that obtain the formation of a specific immune response (Anomy)

Ag determinants (epitopes) are the particular chemical groups on a molecule that are antigenic

Antibody(Ab)/immunoglobulin (Ig).A special group of soluble proteins that are produced in response to foreign antigens (substances)

Definitions/terminology

Antigen and antibody

5 classes of IGs1.IgM (first exposure, large, not passing placenta, huge amont)

2.IgG (secondary exposure, small, passing placenta)

1.IgD (proteins in the plasma membranes of mature B-lymphocytes, same time as IgM)

1.IgA (mucosal immunity, respiratory tract)

1. IgE (Allergy and parasites)

Haptens

Vaccine conjugate

Ministry of defence of the human body

Antibody Protection of the Host

Primary and secondary antibodies P: antibodies raised against an antigenic target of interest and are typically unconjugated. S: antibody that binds to primary antibodies or antibody fragments. They are typically labeled with probes that make them useful for detection,

Immune Precipitation

Antigen

Antibody

Agglutination

RBC

RBC

RBC

RBC

IgM Antibody IgM Antibody

IgG Antibody IgG Antibody

RBC

RBC RBC

RBC RBC

RBC RBC

Factors influencing immunogenicity

Class Switching

antibody titer

time

IgGIgG IgMIgM

Biological mechanism that changes a B cell's production of antibody from one class to another, for example, from IgM to IgG.

Four phases of the primary response

• lag phase where no antibody is detected• log phase in which the antibody titer rises

logarithmically• plateau phase during which the antibody titer

stabilizes• phase (decline) during which the antibody is

cleared or catabilized

Kinetics of the Ab ResponseT-dependent Ag; 1o Response

• Lag • Log

• Plateau

• Decline Ag

D a y s A f t e r I m m u n i z a t i o n

A b

T

i t

e r

LAG LOG DECLINEPLATEAU

Kinetics of the Ab ResponseT-dependent Ag; 2o Response

• Lag

• Log

• Plateau

• Decline

1o Ag 2o Ag

D a y s A f t e r I m m u n i z a t i o n

A b

T

i t

e r

Major practical applications of immunology

– Use of antiserum and vaccination to provide protection against disease.

– Diagnostic tool to detect disease.

– Epidemiological investigation of vaccine preventable diseases

My face is my fortune

Where are you going, my pretty maid?I’m going a-milking, sir, she said

May I go with you, my pretty maid?You’re kindly welcome, sir, she said

What is your father, my pretty maid?My father is a farmer, sir, she said

What is your fortune, my pretty maid?My face is my fortune, sir, she said

VariolationThe word ‘variolation’ comes from the Latin word ‘variola’ for

human smallpox.

Discovery of small pox vaccine

Edward Jenner 1780AD Blossom

Types of acquired immunity

Passive – receive Abs made by another 1. natural 2. artificial - γ globulin, hyperimmune serum

ArtificialNatural

Mode of delivery

Advantages Disadvantages

Immune suppressed/deficiency Long term immunity

Herd immunity

Not immediate

Risk of infection

Risk of contamination

Animal ???

Attenuated can revert to their pathogenic form

Advantages and Disadvantages of Active Immunization

Advantages and Disadvantages of Active Immunization

Advantages Disadvantages

serum sicknessimmediate protection

no long term protection

graft vs. host disease

risk of

hepatitis and HIV

Advantages and Disadvantages of Passive Immunization

Advantages and Disadvantages of Passive Immunization

Serology

A science that attempts to detect signs of infection in a patient’s serum such as Ab for a specific microbe

Serological tests based on Abs specifically binding to Ag – Ag of known identity will react with Ab in an

unknown serum sample.– Known Ab can be used to detect Ag in serum

Ag-Ab reactions are visible by clumps, precipitates, color changes or release of radioactivity.

The most effective tests have high specificity and sensitivity.

Enzyme (ELISA) Immunoassay

Antigen Antigen

anti-antigenanti-antigenantibody antibody

Enzyme Enzyme conjugated to conjugated to anti-Ig antibody anti-Ig antibody (“second (“second antibody”) antibody”)

Add Add substrate substrate

for enzymefor enzyme

a) The presence of a specific Ab b) Identification of microbes

Specificity, sensitivity, and cross reactivity

a) Specificity– Ab attaches with great

exact-ness to only one type of Ag.

b) Sensitivity – Ab can locate Ag, even

when it is greatly diluted.c) Cross reactivity

– the ability of an individual antibody combining site to react with more than one antigenic determinant or the ability of a population of antibody molecules to react with more than one antigen.

Examples of serological tests

1. Agglutination tests2. Precipitation tests3. Immunoelectrophoresis4. Western blot tests5. Complement fixation tests6. Immunofluorescence testing7. Immunoassays

Acute infection

Onset of symptoms

Primary infection

Incubation

Days Weeks Months Years

Onset of symptoms

Primary infection

Incubation

IgM

Days Weeks Months Years

Acute infection

Onset of symptoms

Primary infection

Incubation

IgM IgG

Days Weeks Months Years

Acute virus infection

Onset of symptom

s

Primary infection

Incubation

IgM IgG

Days Weeks Months Years

IgG avidity

Avidity = the sum of affinities between:

antibody

and

antigen

Acute virus infection

Onset of symptom

s

Primary infection

Incubation

IgM IgG

Persistence

IgG avidity

Days Weeks Months Years

Secondary infection or reactivation

Onset of symptoms

Primary infection

Viremia

IgM IgG

IgG avidity

Days Weeks Months Years

Secondary infection or reactivation

Time

1 2 1 2 1

IGtitter

IgM2

IgM1

IgG2

IgG1

1/40

1/64

1/800

Q fever

What should you have in mind!!!Tack home massage

Some times Ag x Ab based tests can results in wrong alarm of outbreak ( Salmonella)

Antigen variation is always a problem (Chlamydia, grouping of streptococci)

Cross-reactivity can give wrong information of an outbreak

Any unusual or unexpected results should be confirmed by genetic test

If possible use other methods than serology in an outbreak situation or combine with other methods