Teaching the Immune SystemTeaching the Immune System

What is Immunity?What is Immunity?Immunity

The body’s ability to fight infection and/or foreign invaders by producing antibodies or killing infected cells

Immune SystemThe system in the body responsible for maintaining homeostasis by recognizing harmful from non-harmful organisms producing an appropriate response

Why do you feel Why do you feel ““crummycrummy”” when when

youyou’’re sick?re sick?

Immune SystemImmune System----Organs and TissuesOrgans and Tissues1. Bone Marrow—the primary

source of all blood cells

2. Thymus Gland—site of maturity for T-cells

3. Blood Vessels, Lymph Vessels and Lymph Nodes—travel and storage for immune system cells

4. Spleen and Lymphoid Tissue of Tonsils, Adenoids, Appendix, etc.—gathering site for immune system cells; often where these cells encounter antigens

First Line of Defense: First Line of Defense: Physical BarriersPhysical Barriers

• Skin, including secretions from sebaceous and sweat glands

• Gastric acid of the stomach• Saliva and tears contain anti-microbial

enzymes• Natural flora of intestines out-competes

pathogenic bacteria• Mucus and cilia trap invaders

Second Line of Defense: Second Line of Defense: Inflammatory ResponseInflammatory Response

1. injury

1.

2.3.

4.

5.

1. Injury: pain2. A cry for help: mast cells and histamine3. Counterattack: macrophages 4. Battle: more immune cells5. Healing: platelets, clots

Time, vol 163, no 8

Third Line of Defense: Third Line of Defense: The Immune ResponseThe Immune Response

Some major players:Phagocytes, including Macrophages and Dendritic Cells

•Sample surroundings for pathogens •Digest invaders and present antigens•Use cytokines to signal T-cells and B-cells

Lymphocytes, including T-cells and B-cells•T-cells—Helper T-cells, Cytotoxic or Killer T-cells, Memory T-cells•B-cells—Plasma cells and Memory B-cells

What are Pathogens and Antigens?What are Pathogens and Antigens?

Pathogens are:Biological agents that cause illness, including bacteria, viruses, fungi, parasites, and protozoa

Antigens are:Substances, such as proteins and polysaccharides, that illicit an immune response. Common antigens include allergens and molecules from digested pathogens.

PhagocytesPhagocytes•Produced throughout life by the bone marrow

•Scavengers – remove dead cells and microorganisms

•Involved in all 3 lines of defense

•Macrophages and dendrites initiate immune responses as they display antigens from the pathogens to the lymphocytes

LymphocytesLymphocytes

B-cells mature in bone marrowthen concentrate in lymph nodes and spleenT-cells mature in thymusB and T cells mature then circulate in the blood and lymphCirculation ensures they come into contact with pathogens and each otherB-cells receive signals to produce antibodies against specific antigens

www.niaid.nih.gov

TT--cellscells

Helper T-cells

•Secrete cytokines

•Signal B-cells and other

T-cells

•Stimulate macrophages

Cytotoxic/Killer T-cells

•Kill cells displaying antigen

Memory T-cells

•Remain “on patrol” in body

T-cells are activated by antigen-presenting cells, such as dendritic cells and macrophages. After activation, these cells divide to form:

BB--cellscellsAntibodies are embedded in the plasma membrane of the B-cell. An antigen-presenting cell and a Helper T-cell are required for activation.After activation:

•Membrane receptors recognize the antigen and the B-cell divides rapidly

•Some activated B cells become large PLASMA CELLS and produce antibodies•Some activated B cells become MEMORY CELLS•Memory cells divide rapidly as soon as the antigen is reintroduced.

CytokinesCytokinesCytokines are “communication molecules”that regulate the immune response and inflammation.

Examples:InterleukinInterferonCorticotropin-releasing factor (CRF)Cachectin

Major Major HistocompatibilityHistocompatibility ComplexComplexMHC I and IIMHC I and II

MHC I and II are molecules on cell surfaces that allow the body to differentiate between “self” and “non-self”

During the immune response, antigens become attached to the MHC markers

AntibodiesAntibodies

•Found on surface of B-cells and in blood

•Interact directly with specific antigensthey recognize

•Variable Regions are the binding sites

•Constant Region is the effector– where the pathogen is immobilized

www.niaid.nih.gov

Putting it All Together:Putting it All Together:Mounting an Immune ResponseMounting an Immune Response

If microbes are able to pass through the first and second lines of defense, the first cells they encounter are the phagocytes.

Cellular Immunity vs. Cellular Immunity vs. HumoralHumoral ImmunityImmunity

Carried out by T-CellsHelper T-cells release cytokines and signal B-cells and Killer T-cellsKiller T–cells destroy infected cells

Carried out by B-cellsAntibodies are produced and dumped into blood stream. Antibodies bind to antigens and neutralize pathogens, marking them for destruction.

CellularCellular HumoralHumoral

Macrophages and Dendritic cells Macrophages and Dendritic cells activate Helper Tactivate Helper T--cellscells

Pathogens

Pathogen eaten by macrophage or dendritic cell

Displays portion of pathogen (antigen) on surface

Helper-T cell detects antigen and releases cytokines

Step 1:

Step 2:

Step 3:

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Helper THelper T’’s activate Killer Ts activate Killer T--cellscellsand Band B--cellscells

Activates B- CellActivates

Cytotoxic T- Cell

Memory B-CellMemory T-Cell

Kills Infected CellsAntibodies

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Helper THelper T-- cells activate Bcells activate B--cellscells

The antibody receptors on the B-cell bind to the matching antigen on the surface of a pathogen.

An activated Helper T-cell binds to the antibody-antigen complex and releases cytokines

The B-cell matures to a plasma cell and releases antibodies

www.niaid.nih.gov

Pathogens are Neutralized and Pathogens are Neutralized and Marked for DestructionMarked for Destruction

www.niaid.nih.gov

Memory cells remain in circulationMemory cells remain in circulation

The immune system produces Memory B-cells and Memory T-cells

These memory cells are able to launch the immune response before any symptoms are felt.

www.altered-states.net/.../bcells.bmp

Summary of Immune ResponseSummary of Immune Response

Antigen

Macrophage

Helper T - Cell

Active Cytotoxic T-Cell Active B - Cell

Kills Infected Cells Memory T- Cell Plasma Cell Memory B-Cell

Antibodies

Deactivates Antigens

Phagocytes

Active and Passive ImmunityActive and Passive ImmunityActive Immunity:

Lymphocytes are activated by antigens on the surface of pathogens•Natural-- acquired due to infection

•Artificial– vaccination

Passive Immunity:

Antibodies appear immediately in blood but protection is only temporary•Natural-- placental and colostrum

•Artificial– human antibodies injected

www.niaid.nih.gov

Allergic ResponseAllergic Response

•Allergens – antigenic substances which do no real harm

•Allergens include dust, animal skin, pollen, dust mites, foods

•Histamine from mast cells cause blood vessels to become leaky

•Fluid and white blood cells leave capillaries

•The area becomes hot, red and inflamed

When the immune system responds to harmless substances

Autoimmune ResponseAutoimmune Response

Common autoimmune disorders include:

Rheumatoid Arthritis

Scleroderma

Multiple Sclerosis

Graves’ Disease

Crohn’s Disease

Lupus

Occurs when the immune cells mistake the body’s own cells for foreign invaders

www.niaid.nih.gov

CreditsCreditsAltered States.net

www.altered-states.net/.../bcells.bmp

Cells Alivewww.cellsalive.com

Dennis Kunkel Microscopyhttp://www.denniskunkel.com/product_info.p

hp?products_id=9573

CreditsCreditsNational Cancer Institutehttp://www.cancer.gov/cancertopics/understandingcan

cer/immunesystem

National Institute of Allergy and Infectious Diseases

http://www.niaid.nih.gov/Publications/immune/the_immune_system.pdf

Time Magazine, February 23, 2004, Vol. 163, No. 8http://www.time.com/time/covers/1101040223/#

Diagrams and Diagrams and AnimationsAnimations

Serotec: Regulatory T-cellsCancer Research Institute: HumoralResponseNational Cancer Institute : Cellular ResponseNational Institutes of Health: Allergy and Immune System ResponseTime: Inflammation