The Immune System & Response to Invasion

•IB Learning Objective

•Describe the process of blood clotting

Copyright Pearson Prentice Hall

Platelets and Blood Clotting 

–The body has an internal mechanism to slow bleeding and begin healing. –Bleeding stops because blood has the ability to form a clot.    

–Blood clotting is made possible by plasma proteins and platelets.

Blood Cells

Step 1 in blood clotting

When we cut ourselves, we cut small blood vessels.

When this happens are body forms a clot.

A clot stops us from losing blood and from a foreign pathogen from entering out body.

Step 1 in blood clotting

A wound triggers a cascade of events by which a blood clot is formed.

First platelets collect at the site of the wound.

Platelets are small disc shaped cell fragments

Platelets do not contain a nucleus

Step 2 in blood clotting

PlateletsPlatelets build up at wound and seal off small build up at wound and seal off small breaks in blood vesselsbreaks in blood vessels

Step 3 in blood clotting

Fibrin proteins form a Fibrin proteins form a mesh mesh of fibresof fibres which which traps red traps red blood cellsblood cells. These dry and . These dry and become a become a scab which closes scab which closes the wound.the wound.

Step 4 in blood clotting

Clotting is the mechanism that prevents and blood loss from broken blood vessels.

a) Platelets or damaged cells release a group of proteins called clotting factors. These clotting factors are released into the plasma a wound site.b) Clotting factors activate the enzyme Thrombin from its inactive form prothrombinc) Thrombin turns the soluble plasma protein fibrinogen into its insoluble fibrous form Fibrin.d) Fibrin binds together platelets and blood cells to form a solid 'plug' for the4 wound. This plug is called a clot.

Leukocytes

• Circulate in many parts of our body. Below is a list of parts of the body where you might find leukocytes– Blood vessels (veins, arteries, capillaries)– Walls of tissues– Lymph vessels and nodes– Organs (especially liver & lungs)

IB Assessment Statement

• Outline the principle of challenge and response, clonal selection and memory cells as the basis of immunity.

White Blood Cells

• Our main defence from disease once it is inside of our bodies is are white blood cells, also called leukocytes.

Lymphocytes

• Specialized leucocytes called lymphocytes are responsible for the immune response in our bodies.

• Lymphocytes have the ability to recognize our ‘self’(our own body cells and proteins) and can recognize ‘non-self,’ antigens (foreign molecules or microorganism (bacteria, virus etc……)

How do are Lymphocytes recognize ‘self’ (own body cells & proteins)

• Cells are identified by specific molecules lodged in the outer surface of the cell (plasma) membrane.

• These molecules are called glycoproteins ( a molecule that contains a carbohydrate and a protein)

glycoproteins

• Glycoproteins that identify cells are known as the Major Histocompatability Complex (MHC)

• There are genes on our 6th chromosome that code for our MHC. Thus, our MHC is genetically determined.

• Each of us as a unique MHC on our cells membrane.

Antigen Receptor

• Our Lymphocytes of our immune system have an antigen receptor that recognizes our own MHC antigen and differentiates these from foreign antigens detected in the body.

Immunocompetence

• All lymphocytes develop in bone marrow, they develop Immunocompetence.

• Immunocompetence means they have the ability to recognize one specific antigen ( the bodies antigen or MHC).

• Immunocompetent lymphocytes are stored in the lymph nodes.

Types of Lymphocytes

•Two distinct types of Lymphocytes1. B-Lymphocytes (B-Cells)– secrete antibodies2. T-lymphocytes (T-Cells) – attack infected cells.

What happens when an Antigen Invades the body?

• An invading will eventually reach the tissue and lymph fluid and encounter a lymphocyte with an antigen receptor.

• The lymphocytes will respond by rapidly dividing and growing, leading to a vast numbers of cells producing antibodies

• Antibodies eventually overcome and dispose of the source of foreign antigens.

• Each immune response event produces memory cells.

• Memory cells survive in the body(mostly in the lymph nodes), for years after the event.

• If the same antigen returns, the body is able to respond quickly, using these memory cells.

• We then say that we have immunity to that pathogen.

Steps of Antibody Production Introduction

• B-Cells are the lymphocytes that produce Antibodies.

• If a B-Cells recognizes and binds to a specific Antigen, the B-Cells proliferate into many cells called plasma cells.

• Plasma Cells secret antibodies into the blood stream.

• These process is called the Humoral Immunity.

IB Assessment Statement

• Define active and passive immunity.

Types of Immunity

• There are two types of immunity1. Passive Immunity2. Active Immunity

Passive Immunity

• Passive immunity is due to the acquisition of antibodies from the mother via the placenta and milk.

• Also antibodies can be received by injections.

Active Immunity

• Active immunity is due to the production of antibodies by the organism, after the body’s defence have been exposed to antigens.

Passive vs. Active

• Active Immunity – develops when a person is exposed to microorganisms or foreign substances and the person’s immune system responds.

• Passive Immunity – is acquired when antibodies are transferred from one person to another.

• The recipients do not make the antibodies themselves

Review Active & Passive Immunity

• Is this active or passive immunity?– Antigen enters body….the body produces

antibodies to neutralize antigen.– NATURALLY ACQUIRED --- ACTIVE IMMUNITY

Review Active & Passive Immunity

• Is this active or passive immunity?– Antibodies passes from mother to fetus during

pregnancy – NATURALLY ACQUIRED --- PASSIVE IMMUNITY

Review Active & Passive Immunity

• Is this active or passive immunity?– Weakened or dead fragments of a microbe are

injected into the body….the body produces antibodies to neutralize microbe

– Artificially ACQUIRED --- Active IMMUNITY

Review Active & Passive Immunity

• Is this active or passive immunity?– Antibodies in a serum (i.e. antivenom used to

treat snake bites) are introduced to the body……– Artificially ACQUIRED --- PASSIVE IMMUNITY

IB Assessment Statement

Address the Learning Objective Below:• Explain antibody production

When an Infection Occurs

The antigens of a pathogen bind to the antibodies in the surface membrane of a lymphocyte…

…This activates the lymphocyte.

The active lymphocyte divides by mitosis to produce a clone of many identical cells

MITOSIS

The clone of cells starts to produce large quantities of the same antibody…

… the same antibody needed to defend against the pathogen!

Most microbes have more than one antigen on their surface, so…

…they stimulate more than one type of lymphocyte…

…resulting in the production of many different antibodies.

These are called polyclonal antibodies.

Antibody Production: The Primary Response

Macrophages take in antigen by endocytosis

Antigen

Macrophage

The macrophage processes the antigen and attaches it to a membrane protein called a MHC protein

The MHC protein is moved to the cell surface membrane by exocytosis so that the antigen is displayed on its surface.

MHC protein

Step 1: Antigen Presentation

Helper T-cell binds to macrophage presenting the antigen

Step 2: Activation of Helper T-cell

Helper T-cells have receptors on their cell surface membranes which can bind to antigens presented by macrophages.

receptor

Helper T-cell

Macrophage sends a signal to activate the helper T-cell

Step 3: Activation of B-lymphocytes

B-cells have antibodies in their cell surface membranes

Inactive B-cell

Antibody

Antigens bind to the antibodies in the surface membranes of B-cells

Antigen

An activated helper T-cell with receptors for the same antigen binds to the B-cell

SIGNAL

The helper T-cell sends a signal to the B-cell, activating the B-cell.

Step 4: Proliferation

Plasma cells are activated B-cells with a very extensive network of rough endoplasmic reticulum.

Plasma cells synthesis large amounts of antibody, which they excrete by exocytosis.

The activated B-cell starts to divide by mitosis to form a clone of plasma cells.

The Secondary Response: Memory Cells

• If an antigen invades your body a second time, a much faster response occurs which produces much larger quantity of the required antibody.

•When activated B-cells are dividing during the primary response, some cells stop dividing and secreting antibody and become memory cells.

• Large numbers of memory cells remain in the body for a long time…• …they are capable of producing large amounts of antibody very quickly when stimulated.

B-cell

Macrophage

Antigen

Activate

Antigen

Helper T-cell

Activate

Clone

MemoryCell

Plasma Cell Antibodies

Antibody Production: Summary