Immunology

Immunology

KA 5

KA 6

KA 7

KA 8

Non specific body defences

Pathogens are bacteria, viruses and other organisms that cause disease

The human body has the capacity to protect itself against pathogens, toxins and cancer cells through the immune system

Immunity is the ability of the body to resist infection by a pathogen or destroy the organism if it succeeds in invading and infecting the body

An example of the first line of defence is for the skin to act as a physical barrier to pathogens.

An example of the second line of defence is cellular response, phagocytosis.

Third line defence is the response of T lymphocytes from the Thymus Gland. Also the production of antibodies by B lymphocytes in the bone marrow

The surface of the skin is composed of tightly packed epithelial cells which offer physical protection from pathogens

Mucus membranes that line the digestive and respiratory tracts are also composed of epithelial cells that form a physical barrier

Secretions from the skin provide chemical defence. Like tears, sweat glands, lining of the stomach and saliva

When the body suffers a physical injury such as a cut with/without invasion of microbes, it responds by a localised defence mechanism called an inflammatory response at the effected site.

Mast cells & histamine

Mast cells are produced from the same stem cells as white blood cells. They are present in connective tissue throughout the body and they release histamine

Histamine is a chemical that causes blood vessels to vasodilate and capillaries become more permeable.

After injury, mast cells release large quantities of histamine resulting in blood vessels in the injured area undergoing vasodilation and increased capillary permeability

This is beneficial because it results in an increased accumulation of phagocytes to the affected are and rapid delivery of blood clotting factors to the affected area

Phagocytosis

1. Phagocytes recognise surface antigen molecules present on a pathogen and move towards it.

2. Phagocytes engulf the pathogen by in-folding the membrane creating a vacuole

3. Lysosomes, which contain digestive enzymes to digest the 'foreign' pathogen

4. The breakdown products are absorbed by the phagocyte

5. Phagocytes release cytokines, cytokines attract more phagocytes to the affected area.

Lymphocytes are white blood cells that carry out a specific immune response and are produced by stem cells

There are 2 types of lymphocytes. T & B lymphocytes

T lymphocytes

B lymphocytes produce antibodies against antigens. They are Y-shaped. Antibodies inactivate the pathogens which are later destroyed via phagocytosis.

An allergic reaction occurs when B lymphocytes act on an antigen that is harmless to the body, such as pollen.

These recognise antigens on the pathogens membrane resulting in apoptosis, cell death. The remains are destroyed by phagocytosis

Failure of regulations in the immune system results in T lymphocytes acting on self-antigens, causing auto-immune diseases.

Cloned lymphocytes produced in response antigens survive long term, as memory cells. So if the body has a second exposure, the memory cells will recognise the antigens, resulting in the individual not showing symptoms.

The first exposure is known as the primary response, without any cloned lymphocytes resulting in a more serious illness. The secondary response is the memory cells preventing symptoms.

HIV, this is when T lymphocytes are attacked and destroyed, this then leads to AIDS. The immune system starts to shut down gradually.

There are 4 types of immunisation.

1. Passive Natural: Immediate protection, short term, eg. antibodies from placenta.

2. Active Natural: Develop after lag time, long lasting, includes memory cells, eg. natural exposure to chicken pox.

3. Passive Artificial: Immediate protection, short term, needs medical treatment, eg. tetanus.

4. Active Artificial: Develop after lag time, long lasting, needs medical treatment, eg. whooping cough & MMR.

Immunity is developed through vaccines. There are 4 ways in which the antigens are exposed to the body.

1. Inactivated pathogen toxin: Tetanus & Diphtheria

2. Dead pathogen: Hepatitis A

3. Parts of pathogen: Hepatitis B & HPV

4. Weakened pathogen: MMR

Adjuvants are added to vaccines to make them more effective, resulting in increased immunity

Herd immunity is protecting and immunising those who aren't protected. This is important because if a large percentage are protected, the spread is reduced.

The herd immunity threshold is the point in which a minority of a population is unimmunised in order for the pathogens to be resisted. Mass vaccination programmes are held to increase Herd Immunity.

Antigenic variation is when the antigens of a pathogen changes such as the flu. It is recommended that individuals who are vulnerable are immunised annually.

Clinical trials are held to ensure that a vaccine is effective

Double blind, randomisation and placebo control are types of clinical trials.

Double blind: Doctors/individuals don't know who is getting what

Randomisation: Health info is hidden to prevent bias

Placebo Control: Person is given this to see if psychological effects results.

A computer is used to reduce experimental error, ensuring the trials are fair.