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Immunity: Defense against disease

EL: To bring together the learnings on immunity from SAC 4

What is Immunity?

Definitions

Immunity The ability of the body to fight infection

and/or foreign invaders by producing antibodies or killing infected cells.

Immune System The system in the body responsible for

maintaining homeostasis by recognizing harmful from non-harmful organisms and produces an appropriate response.

Foreign Invaders

Pathogens Cellular or non-cellular

agents that cause disease/immune response.

Antigens Compounds, usually

proteins, on the outside of pathogens that can trigger the immune system to respond.

+Major Parts of the Immune System

1. Blood - White Blood Cells in particular.

2. Lymphatic system - vessels carry a type of fluid named lymph, which bathes the tissue of the body and also is a ‘transport network’ for immune cells.

3. Lymph nodes - the centre of activity where lymphocytes (a type of white blood cell) are continually circulating from tissue in the body, to the lymph nodes and back again by using the bloodstream and lymphatic vessels.

4. Thymus Gland – Produces T Lymphocytes

5. Bone Marrow – Produces B Lymphocytes

•Self= cells and other substances that are a part of the organism and carry “self” markers •Non-self = organisms, cells and other substances that are not part of the organism.

•The invading cells carry molecules (antigens) that the immune system is able to detect as ‘non-self.’

What is self and non-self?

Major Histocompatibility Complex

• Simple terms: Major Histocompatibility complex is a cluster of genes that produce proteins that form the markers on our cells. These markers are known as MHC Class 1 molecules.

• Each person’s MHC markers are different

MHC

Inside the cell...

MHC marker protein recognised

BANG!!R.I.P.

Edward Non-Self

How does the body fight pathogens?

The Body’s THREE lines of Defense

FIRST LINE

SECOND LINE

THIRD LINE

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Pathogen Invades Tissue

Non-Specific Defences

Barriers to EntrySkinMucousSecretionsNatural Flora

Physiological MechanismsFever

Chemical Mechanisms Complement proteins Interferons

MechanismsPhagocytes (granulocytes,Macrophages), Natural killer cells (cytotoxic)

Inflammation Mast cellsRelease of Histamine

Specific Defences

Second line of defenseFirst line of defense

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Pathogen Invades Tissue

Non-Specific Defences

B-cells T-cells

Specific Defences

Third line of defense

Plasma cells – produce antibodies

Memory cells – remember antigen

Helper T-cells (Th) - stimulate B cells

Cytotoxic t-cells (Tc) kill body cells infected with a pathogen

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ANTIGENS: Any substance foreign to the body that triggers a response from the immune system, such as producing antibodies in order to neutralise it.

- Also known as immunogens- Usually made up of proteins but can be polysaccharides- All have unique shapes- A way to remember:antigens = antibody generators- Antibodies are generated to attack thepathogen behind the antigen being detected

Back to Antigens.

Antibodies/Immunoglobulins

The third line of defense involves the production of antibodies:

Y-shaped protein molecules

Produced by B-cells

Made up of variable (recognizes antigen) and constant regions.

Function: Recognize antigens, bind to and deactivate them.

+ANTIGENS AND ANTIBODIES.

+ANTIGENS AND ANTIBODIES.

http://www.youtube.com/watch?v=Ys_V6FcYD5I

+IgG IgA IgM IgD IgE

Approx. Concentration in serum (mg/mL) 12 2 1 0.04 0.000.02

Ability to cross placenta yes no no no no

Present in saliva and tears no yes no no no

Present in milk yes yes no no no

Active against viruses yes yes some no no

Active against some bacteria yes yes yes no no

Involved in allergy reaction no no no no yes

The Pathway of Specific Immune Response

Pathogens

Pathogens eaten by Macrophage

Macrophage displays portion of Pathogen on surface (antigen)

Helper-T cell recognizes Pathogen

Step 3

Activates B- CellActivates Cytotoxic

T- Cell

Memory B-CellMemory T-Cell

Kills Infected CellsAntibodies

+Immune Response Summary1. Antigen infects cells.

2. Macrophage ingests antigen and displays portion on its surface.

3. Helper T- Cell recognizes antigen on the surface of the macrophage and becomes active.

4. Active Helper T-Cell activates Cytotoxic T-Cells and B-Cells.

5. Cytotoxic T-Cells divide into Active Cytotoxic T-cells and Memory T – Cells.

6. Active Cytotoxic T-Cells kill infected cells.

7. At the same time, B-Cells divide into Plasma Cells and Memory B- Cells.

8. Plasma cells produce antibodies that deactivate pathogen.

9. Memory T and Memory B cells remain in the body to speed up the response if the same antigen reappears.

10. Supressor T-Cells stop the immune response when all antigens have been destroyed.

Immune Response Summary

Antigen

Helper T - Cell

Active Cytotoxic T-Cell Active B - Cell

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

Antibodies

Deactivates Antigens

Displays copy of antigen on surface of cell

Cellular ImmunityHumoral Immunity

+Clonal selection

+Acquiring immunity

Long lasting vaccines

Short lasting vaccines

+Autoimmune Diseases

Autoimmune diseases cause antibodies in the immune system to act against the body’s tissues!

There are 80 different types (e.g. MS, Chrohn’s disease etc)

The cause is unknown…

BUT, it is genetic and can pass through your family.

An autoimmune disorder may result in:

-The destruction of body tissue

-Abnormal growth of an organ

-Changes in organ function

+Immunonodeficiency diseases

Immunodeficiency refers to a malfunction or deficiency in one or more components of the immune system.

PRIMARY IMMUNODEFICIENCY:Disorders where part of the immune system is missing or not functioning properly. Most are genetic disorders.

SECONDARY IMMUNODEFICIENCY:Same as Primary Immunodeficiency, but is caused by a secondary nature, e.g. caused by another disease, drug treatment or environmental exposure to toxins (e.g. HIV leading to AIDS)

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