Viruses and other infectious agents have developed many ways to escape the immune system, but the immune system also has a lot of clever strategies

An Evolutionary Arms Race

Day ofImmunology

Infection Immune system

Credits: Ahmed Sheriff, Deniz Zeisig, Susanne Bürgis, Alexandros Theodoridis, Tobias Strapatsas, Hans-Martin Jäck, Aaron Marshall

basic immunologyDGfI

Day ofImmunology

Pandemic: Spanish Flu 1918/1919

Estimated 40 Million dead

Day ofImmunology

Infectious microbes are everywhere: Bacteria, viruses, fungi, parasites

How does the body defend itself against these invaders?

With the help of the

Immune system

Influenza virus Salmonella bacterium

Day ofImmunology

Day ofImmunology

Our Immune System can also defend us against cancer arising in the body

A T cell (orange) killing a cancer cell (mauve)

When the immune system errs...

Day ofImmunology

Allergy happens when the immune system mistakenly “defends” against a microbe that’s not really a microbe: pollen, house dust, cat hair, specific foods…

A very widespread problem, and rising: up to 30% of the population in some developed countries

ALLERGYALLERGY

Why do some people´s immune systems give allergic reactions, but not others?

Day ofImmunology

Rheumatoid arthritis (joints) Inflammatory bowel disease (intestine) Type I diabetes (pancreas) Multiple sclerosis (brain and spinal cord) Systemic lupus erythrematosus (multiple tissues)

It is also important to know how we can turn an over-active immune system OFF!

When the immune system errs...

AutoimmunityAutoimmunity

Know your immune system! What is it really?Know your immune system! What is it really?

Consists of certain substances and cells in the body, that each provide different kinds of defenses against

pathogens

The armed forces of the body:

• White Blood Cells such as B-cells and T-cells (Lymphocytes)

• Phagocytes

• Blood proteins

• Antibodies

Day ofImmunology

(I) Innate Immunity

Barriers

Blood proteins

Phagocytes

(II) Acquired immunity

B- and T-Cells

Day ofImmunology

Defence mechanisms against infectionsDefence mechanisms against infections

(I) Innate Immunity - Barriers(I) Innate Immunity - Barriers

Skin

Saliva

Stomach acid

Intestinal flora

Pathogens find ways to penetrate body barriers!

Day ofImmunology

(I) Innate Immunity = immediate defence reactions (I) Innate Immunity = immediate defence reactions

Phagocytes, also known as macrophages

Microbes become food!

Attract more phagocytes

Release messenger molecules that affect the whole body (Interleukins)

Fever, new formation of phagocytes, opening of local blood vessels

HELP

Proteins from the blood attach to microbes

marking of the microbes for phagocytes (eat me!)

direct destruction of microbes

Day ofImmunology

Characteristics of inflammation: Redness, swelling, pain, heat

Inflammation brings rapid assistance

A wound = a call to arms!A wound = a call to arms!

The fight begins against growth and spreading of the pathogens : phagocytes are called in, wound healing is started

Day ofImmunology

Defence mechanisms against infectionsDefence mechanisms against infections

Ready to fight many pathogens

Day ofImmunology

(I) Innate Immunity

Barriers

Blood proteins

Phagocytes

(II) Acquired immunity

Activation of specific immune cells:

B- and T-Cells

Need to learn how to fight eachnew pathogen (and can rememberafterwards!)

(II) Aquired immunity - the Lymph System(II) Aquired immunity - the Lymph System

Tonsils

HeartThymus

Kidney

Appendix

Lymph nodes

SpleenPeyers Patches

Bone Marrow

• Thymus

• Bone Marrow

• Lymph nodes

• Spleen

• Tonsils

• Appendix

Lymph nodes

Adenoids

Day ofImmunology

(II) Aquired immunity = a custom-tailored defensive (II) Aquired immunity = a custom-tailored defensive strategystrategy

Initiation

Phagocytes and dendritic cells alert B and T cells

Activation!

ZZZ

Z

Who needs my

help?

ZZZZ

T

Day ofImmunology

T-cells get into the action T-cells get into the action

Activation of B cell Antibody production

Destruction of the infected cells

T-cell

Killer T-cell Helper T-cell

Asta la vista, baby!

Day ofImmunology

B-cells get into the actionB-cells get into the action

Interaction of B-cell and T-Helper cell in lymph node

B cell becomes a plasma cellAntibodes are produced to

neutralize the invader!

Finally you‘re here!

Here comes help!T

Day ofImmunology

Influenza Virus

Antibodies bind to surface projectionsneutralizing the virus

Day ofImmunology

Lock-and-Key Principle

Day ofImmunology

The immune system has a memory The immune system has a memory

! The immune system can learn !

Memory B- and T-cells can remember the invading microbe for years.

Therefore next time the same microbe is encountered, one can fight it off faster and more effectively. Think vaccination!!!

TB

Day ofImmunology

Y

Y Y

Y

BUT - Viruses routinely use small variations to evade immune memory!

Small variations in the Virus genes

Y

YY

Y

Small variations in the virus surface structure

Reduced protection by Antibody

Day ofImmunology

Bird cell

OR RARELY - Large change to completely escape immunity:

Y

YY

Y

Day ofImmunology

Large variations in the Virus genes occur in another species

Completely different virus surface structures

NO protection by Antibody - Bird flu pandemic!

Fast

Specific for type of microbe

Constant level of protection

Takes time to develop

Specific for exact microbe

Memory for strong protection in the future

Day ofImmunology

Defence mechanisms against infectionsDefence mechanisms against infections

(I) Innate Immunity

Barriers

Blood proteins

Phagocytes

(II) Acquired immunity

Activation of specific immune cells:

B- and T-Cells

What causes allergy?

B cell meets an Allergen and produces antibodies

-> WHY do B cells sometimes mistake Allergens for Pathogens?

Day ofImmunology

Pollen

Mast cells bind these antibodies on their surface

Day ofImmunology

When the loaded mast cells come into contact with allergen they are activated and produce histamine

Histamine

Day ofImmunology

Allergy symptoms

Why do some people‘s immune systems give allergic reactions, but not others?

GenesEnvironmental exposure to allergensAir pollutionSmoking???

?Day of

Immunology

How can we reverse immune responses to allergens?

How do we turn off autoimmunity without completely destroying the immune system?

Can we mobilize the immune system to fight off cancer?

How can we quickly mobilize the immune system to fight new emerging infectious diseases? SARS, bird flu

How to develop vaccines for chronic infections such as HIV?

Questions

Day ofImmunology

We’re working on it!

?Day of

Immunology

Your Questions?