1. Defence Against Disease HL
Clotting:
Begins with the release of clotting factors from either the damaged tissue or from platelets (cell fragments that circulate in the plasma). This sets off a series of reactions which is summarized below:

2. The product of each reaction is the catalyst for the next reaction
The product of each reaction is the catalyst for the next reaction. In the last reaction, the soluble fibrinogen molecule has its negative peptide groups removed, and this allows it to bond to other fibrinogen molecules. This forms long protein fibres called fibrin, which form a mesh across the wound. This traps blood cells and a clot forms.

3. Immunity: Immunity is the body’s resistance to infection.
When a pathogen invades the body, the immune system is challenged and produces antibodies against the pathogen as a response.
Macrophages are the first
white blood cells to encounter
the pathogen and they ingest
it. As a result, the antigen of the
ingested pathogen is displayed
on the surface of the
macrophage. It will then travel to
a lymph node.

4. The body contains a large range of B lymphocytes (B cells) and T lymphocytes (T cells). Specific receptors on each B and T cell differ slightly from each other due to the variation in the proteins at their surface. Consequently, it is estimated that we have up to one million different B cells and 10 million different T cells to cope with the antigens that enter the body.
The macrophage displaying the antigen on its surface selects a T- helper cell that has receptors matching the antigen. These T – helper cells divide by mitosis and activate B cells with the same receptor to the antigen.
The B cells form a clone.
Some differentiate into plasma cells, which produce antibodies
Some differentiate into memory cells and are stored.
Clonal selection - the process of the macrophage selecting the T cells and B cells which have the required surface receptor

5. Clonal expansion – the process of T cells and B cells forming clones to produce the large numbers of cells that are required to deal with the infection. Antibody Production 1. Macrophages ingest antigens by endocytosis and attach them to membrane proteins called MHC proteins. These are moved to the outer surface of the macrophage by exocytosis.

7. 2. Helper T-cell activation Helper T-cells with receptors specific to the antigen presented by the macrophage attach to the antigen. The macrophage then sends a message to the helper T-cell and changes it from an inactive form to an active form. MHC (Major Histocompatability Complex) proteins are membrane proteins found on macrophages. Helper t cell receptors do not respond to antigens unless the antigen matches the MHC protein on the macrophage.

8. 3. B-cell activation B-cells have antibodies in their plasma membrane which bind to antigens. An activated T-cell with receptors for the same antigen binds to the B-cell and activates it. 4. Plasma cell production Activated B-cells divide by mitosis to form clones of plasma cells. These produce large numbers of antibodies which are secreted by exocytosis.

9. 5. Memory cells Some of the activated B-cells and helper T-cells become memory cells. These persist in the body once the infection has been fought and are stored in the lymph nodes. These allow a rapid response if the disease is encountered again. Cytotoxic T-cells: These cells are lymphocytes that are able to detect viral proteins in the membrane of infected body cells and then destroy them. They can also detect some types of cancer cells and destroy them. Immune System (CMIR & AMIR) - YouTube

10. Types of Immunity: Natural – Results from the infection caused by a pathogen. eg/ The body is immune to chicken pox after being infected by it. Artificial – Results from inoculation with a vaccine. eg/ The body becomes immune to the chicken pox virus after being vaccinated for it. Active – The body produces antibodies in response to an infection. eg/ Infection with the measles virus causes immunity and re-infection is very rare. Passive – Antiboides are received from another organism. eg/ During pregnancy, antibodies are passed to the foetus across the placenta. The first milk produced (colostrum) also contains antibodies which the baby absorbs from its stomach.

11. Production of Monoclonal Antibodies:
Definition - Any of the highly specific antibodies produced in large quantity by the clones of a single hybrid cell formed in the laboratory.
Large amounts of a single type of antibody can be made by the following technique:
Antigens corresponding to
the desired antibody are
injected into the body of an
animal.
Plasma B-cells producing
the desired antibodies are
extracted from the animal.

12. 3. The B-cells are fused with tumour cells, producing hybridoma cells
3. The B-cells are fused with tumour cells, producing hybridoma cells. These divide and produce the antibody.
The hybridoma cells are cultured and the antibodies produced are extracted and purified.
Monoclonal antibodies are used in both the diagnosis and treatment of diseases.
Diagnosis. (eg/ malaria)
Monoclonal antibodies are produced that correspond to antigens in the malarial parasite. These are fixed to an agar plate, and a blood sample is added. Any antigens in the sample will bind to the antibodies.
A second type of monoclonal antibody is added, which has enzymes attached to it which cause a colour change. This allows detection of the antigen. This is called an ELISA test.

13. Treatment. (eg/ cancer)
Monoclonal antibodies are produced that correspond to the antigens in cancer cells. These are then attached to drugs that destroy the cancer cells, and the antibodies are injected into the bloodstream.
Monoclonal Antibody Production – YouTube

14. Vaccination. A vaccine is a modified and harmless version of a pathogen that stimulates the body to develop immunity without developing symptoms of the disease. Antigens in the vaccine stimulate the production of antibodies. Sometimes, two or more vaccinations are needed to produce enough antibodies. The end result is production of memory cells which provide long term immunity.

15. Benefits.
Some diseases can be completely eradicated. (eg/ smallpox)
Deaths due to disease can be prevented. (eg/ measles is no longer a major cause of death to infants in most parts of the world)
Long term disabilities due to disease can be eradicated. (eg/ rubella in pregnant women caused deafness, blindness, heart disease and brain damage in babies)
Dangers.
Multiple vaccinations may reduce the capacity of the immune system to respond to new diseases.
Immunity developed after vaccination may not be as effective as immunity due to catching the disease. Children who are vaccinated may become susceptible to the disease as an adult.

16. Some side effects may develop from vaccines
Some side effects may develop from vaccines. (eg/ MMR vaccine – measles, mumps and rubella) may lead to autism. Whooping cough vaccine may cause brain damage.)