Immunity

Non-specific immunity

Ø  Many pathogens cannot cause disease due to non specific barriers and cellular defences, that prevent them from entering the body

Ø  Physical barriers- prevent entry of pathogens and micro-organisms when they are in contact. (1st line of defence)

o   Tears

o   Eyelashes

o   Skin

o   Mucous

o   Ciliated cells

Ø  Skin- dry and strong, outer layers of cells are shed taking bacteria with them.

Ø  Eye lashes- respond to foreign bodies in the region of the eyes

Ø  Mucous- traps dirt and bacteria

Ø  Cilia- brushes the trapped dirt and bacteria away

Ø  Tears- lysosomes which destroy bacterial cells

Ø  HCL- present in stomach acid

Ø  Skin:

o   Secretes sebum which lowers the pH- inhibits pathogen growth

o   Sweat contains salts- hard for certain types of bacteria to survive

Ø  Tears and eye lashes:

o   Tears contain lysosomes which are enzymes that can destroy bacterial cells and prevents entry of pathogens in the eye

o   Eye lashes respond to foreign bodies near the eyes by blinking

o   Conjunctiva is a strong thin layer over the eyes

Ø  Respiratory tract:

o   Mucous and ciliated cells

Ø  Digestive system:

o   Stomach acid which lowers the pH (1.5 to 2.5) so is in an inhospitable environment for bacteria to survive

Ø  Phagocytosis is the process in which invading microorganisms are engulfed and destroyed by specific white blood cells known as phagocytes (2nd line of defence is phagocytosis)

 Antibodies:

Agglutination- antibodies can cause microbes to stick together

This makes it easier for phagocytes to engulf them

Neutralisation- some pathogens make us ill by producing toxins

Some antibodies work by neutralising these toxins

Opsonisation- the binding of an antibody to the surface of a pathogen can set of a chain reaction with blood proteins which causes the pathogen to swell up and burst.

Antibody Production:
Macrophage engulfs a microbe by endocytosis, digests the microbe and processes its antigens. The processed antigens are then attached to a MHC protein. This MHC is then moved to the cell surface so that the antigen is displayed on the surface of the macrophage. A helper T cell then binds to the antigen presented on the surface of the macrophage which causes the macrophage to release a signal which activates the helper T cell. B cells have antibodies on their cell surface membrane, therefore antigens will bind to the antibodies on the surface of the B cells. This means that an activates Helper T cells with receptors for the same antigen can bind to the B-cell. When this happens, the helper T cell sends a signal to the B-cell, activating the B cell. The activated B cell then starts to divide by mitosis to form a clone of plasma cells. Plasma cells are activating B cells with a very extensive network of rough endoplasmic reticulum. These cells can synthesise large amounts of antibodies which they excrete by exocytosis.

Distinguish clearly between an antigen and an antibody

An antigen is a foreign substance that induces an immune response in the body, whereas an antibodies are specific proteins released by plasma cells that can attach to pathogenic antigens.

Why is it important that some opsonins are not very specific?
Opsonins are a group of antibodies that bind to the antigens on a pathogen. It is important they are not very specific as well because they are quicker and can attack a wide variety of pathogens.

Immunoglobulin: Antibodies are immunoglobulins- complex protein produced by the plasma cells in the immune system. They are released in response to an infection. 

How are plasma cells specialised for their job?
Plasma cells are activating B cells with a very extensive network of rough endoplasmic reticulum. Rough E.R. is needed for protein production, which is necessary for the production of antibodies, which are proteins. Also a large number of ribosomes for making the antibodies from the code in the DNA. Also more Golgi apparatus which modifies and packages the proteins. Mitochondria is also present in large numbers to provide energy for exocytosis as it changes the shape of the cytoskeleton.

The antibodies and antigens must be complementary so that the antibodies can attach to the antigens and render them harmless. It must be complementary so that they can bind together as our immune system manufactures one type of antibody for every antigen.

How are antibodies structure helpful to carry out their function?
The antibody has a variable region that is different for all antibodies because that region must be complementary to the shape of the antigen. There is a constant region that remains the same in all antibodies which makes it easier to bind with phagocytic cells. The antibody can grip more than one antigen due to the hinge region which allows flexibility.

Why does it take several days for the primary immune response to become effective?
Antibodies are produced in response to infection, so when the immune system detects an infection it begins to release antibodies. However, it may take days for the number of antibodies to rise to a level that can combat the infection successfully. This is known s primary immune response.

It’s a long series: Macrophages, Helper T cells, B cells, Plasma cells and then antibodies.

Vaccination

Vaccinations provide immunity to specific diseases. This is created by deliberate exposure to antigenic material that has been rendered harmless. The antigenic material material is usually injected, but in some cases is taken orally. The immune system treats it as a real disease so the immune system is activated resulting in it manufacturing antibodies and memory cells. The memory cells provide the long term immunity.

The antigenic material used in vaccines can take a variety of forms:

Whole living organisms- not as harmful as those that cause real disease, but must have similar antigens so that the antibodies produced will be effective against the real pathogen.

A harmless or attenuated (weakened) version of the pathogenic organism. Ex. Measles and TB

A dead pathogen- Typhoid and cholera

A preparation of the antigens from a pathogen- Hepatitis B

A toxoid, which is a harmless version of a toxin- tetanus

Application of vaccines

Herd Vaccines:
Using a vaccine to provide immunity to all or almost all of the population at risk. Once enough people are immune, the disease can no longer spread in the population and you achieve herd immunity. In order for it to be effective, it is essential to vaccinate almost all the population. It is estimates that at least 95% of the population would need to be immunised in order to prevent the spread of measles.

In the UK, there is a vaccination programme to immunise young children against the following diseases: tetanus, whooping cough, polio, meningitis, pumps, measles, rubella and diphtheria.

Ring Vaccine:
It is used when a new case of a disease is reported. It involves vaccinating all the people in the immediate vicinity of the new case. It is used in many parts of the world to control the spread of livestock disease.

Control of epidemics:
Once a disease has been eradicated, or reduced to such a low incidence that it is unlikely to spread, the routine vaccination programme can be relaxed. However, some pathogens can undergo genetic mutations which change their antigens. The memory cells produced by vaccinations may not recognise the new antigens. When this occurs the pathogen may be transmitted and the incidence of the disease increases.

Certain pathogens such as influenza virus are relatively unstable so regularly change their antigens. When this occurs, an epidemic may arise. Threats of epidemics must be monitored so that the new strains of pathogens can be identified. This enables the health authorities to prepare for an impending epidemic by stockpiling suitable vaccines and vaccinating people who are at particular risk of the disease.

In attempts to avoid another worldwide epidemic (pandemic), people at risk are immunised. In the UK there is a vaccination programme to immunise all those aged over 65 and those who are at risk for any other reason. 

Different types of immunity

Immunity can be achieved naturally or artificially. Natural immunity is achieved through normal life processes. Artificial immunity is achieved through medical intervention. It can also be achieved passively or actively. Active immunity us achieved when the immune system is activated and manufactures its own antibodies. Passive immunity is achieved when the antibodies are supplied by another source.

	Natural	Artificial
Active	Immunity provided by antibodies made in the immune system as a result of infection. A person suffers from the disease once and is them immune- ex. Chicken pox	Immunity provided by antibodies made in the body as a result of vaccination. A person is injected with a weakened, dead or similar pathogen, or with antigens, and this activates his/her immune system.
Passive	Antibodies provided via the placenta or via breast milk. Thus makes the baby immune to disease to which the mother is immune. It is very useful in the first year of the baby’s life, when its immune system is developing.	Immunity provided by injection of antibodies made by another individual. Tetanus can also be treated this way when vaccination using a toxoid has not worked well.

1.     Threats of new cases of disease have to be reported so that the new strains of the pathogens can be identified. This makes sure that the health authorities can prepare for an impending epidemic by stockpiling the necessary vaccines and vaccinating people who are at risk from getting the disease or vaccinating most of the population so that the disease cannot spread.

2.     Using a living organism for vaccinations that are not as harmful as the real ones can cause an immune response that is similar to that of the real disease. They normally produce immunity in most recipients with one dose, except if its not a living pathogen that a second dose is recommended to provide a high level of immunity.  There is a higher chance of the antibodies produced by the immune response to be effective against the real pathogen.

3.     Herd vaccination is using a vaccine to provide immunity to all or almost all of the population at risk. Once enough people are immune the measles pathogen can no longer be spread through the population. If 95% of the population is immunised, then the pathogen cannot spread.

4.     Passive immunity is achieved when the antibodies supplied are from another source. The recipient will only temporarily benefit from passive immunity for as long as the antibodies persist in their circulation. It is temporary and will last a few months at most, this is because they are not your own antibodies and they will be removed by the body. It provides effective protection and will decrease over time.

5.     People over 65 years of age and those with respiratory tract conditions are particularly at risk from getting influenza. Medical chronic conditions such as asthma, heart disease, blood disorders, kidney disorders, metabolic disorders etc. People with a BMI of 40 or more have an increased risk of complications from influenza. Pregnant women are more likely to develop influenza complications, particularly in the second and third trimesters.