Defence Against Pathogens
Human Biology (Year 12)
What are specific defences against disease?
Specific defences are those directed towards a particular pathogen, for example, if you get infected with the chickenpox virus, the body will make antibodies which are only effective against the virus in order to combat it. Specific defences are part of our immune system, which is composed of cells and proteins which protect us against foreign organisms, a range of alien chemicals, as well as cancerous and other abnormal cells.
Some of these cells are non-specific, such as phagocytes, which are able to engulf and digest micro-organisms and cell debris
However, others such as B-cells and T-cells only provide protection against a specific micro-organism or disease-causing substance
When these cells react, it is called the immune response
What is the immune response?
The immune response is a homeostatic mechanism, and when micro-organisms or foreign substances enter the body, the immune response helps to deal with the invasion and restore the internal environment to its normal condition.
The key cells involved in the immune response are B-cells and T-cells, which are white blood cells called lymphocytes.
B-cells and T-cells are produced in the bone marrow and end up in the lymphoid tissue, however they mature in different routes
Approximately 50% of the cells produced by the bone marrow go to the thymus where they mature into T-cells before being incorporated into the lymphoid tissues
The other half of the cells mature in the bone marrow to become B-cells and then become part of the lymphoid tissues
Most of the lymphoid tissue is in the lymph nodes, however it also occurs in other parts of the body such as the spleen, thymus gland and tonsils
There are two components of the immune response;
The humoral response or antibody-mediated immunity involves the production of special proteins called antibodies by B-cells which circulate around the body and attack invading agents
The cell-mediated response is due to T-cells and involves the formation of special lymphocytes that destroy invading agents.
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