Immunity

The specific immune response helps to destroy any invading pathogens. The body responds in a non-specific way in four ways:

• Inflammation: Damaged white blood cells release histamine which causes blood vessels to dilate and capillaries to become more permeable. This increases blood flow to the damaged area. Increased blood flow causes plasma fluid to be pushed out of the blood vessels and into the tissues, which results in a swelling called oedema. 
• Lysozyme action: Lysozymes are enzymes found in tears, sweat and in the nose. They're able to trap and destroy bacteria by breaking down the cell walls. 
• Interferon: Provides a non-specific response against invading viruses. Virus infected cells produce the chemical and it diffuses into surrounding cells where it prevents viruses from multiplying. 
• Phagocytosis: Phagocytes such as neutrophils and macrophages engulf bacteria, surrounding them in a vacuole.They're then able to release enzymes which destroy the bacterial cells. 

The specific immune response involves the action of lymphocytes. The specific immune response involves several stages. 

Activation of T-helper cells: T-helper cells use their CD4 receptors to attach to APCs (macrophages). This causes the T-helper cell to become activated, dividing producing active cells and T-memory cells.

Clonal selection: APC B cells have complementary receptor to activated T-helper cells and they bind. This releases cytokines and produces B memory cells and B effector cells. The B effector cells then differentiate into plasma cells which can produce antibodies. 

T-killer cells: Infected cells displaying the antigen of the bacteria on their surface are then labelled by the antibodies produced, and T-killer cells have a complementary receptor and bind to them. This produces T-killer memory cells and active T-killer cells which then go on to bind to the infected cells and release chemicals which cause a pore to form in the cell, initiating cell lysis. 

Active Natural: Develops when a person is exposed to an antigen by physically developing the disease/illness. The body produces memory cells which are able to help defend the body against future illness.. 

Active Artificial: An injection of a dead or attenuated version of disease organisms are given. Exposure to the antigen means memory cells can be produced. 

Passive Natural: Antibodies are passed on from the mother in breastmilk. They protect against invading pathogens the mother may have come into contact with. 

Passive Artificial: The person is injected with antibodies without the need to make them themselves. It can provide immediate protection againat the invading pathogen they're specific for.