Edexcel A2 Biology SNAB 6BI04 ~ 6BIO5 June 2016

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They are a type of lymphocytes which mature in the Thymus (hence the name T-cells)

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They can be subdivided into T-helper cells, T-killer cells and T-memory cells

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They are involved in the activation of B-cells and T-killer cells:

1.

The macrophage is able to recognise the foreign antigen in the body.

2.

They engulf the foreign antigen in the process of phagocytosis (they engulf, cause the antigen to be enclosed in a vacoule known as phagosome then lysosyme fuses with the phagosome and causes enzymes to be released into the phagosome. These enzymes breakdown the antigen.)

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Then some of these proteins are presented on the MHC which is on the cell surface membrane.

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The T-helper cell binds to this using its CD4 receptors

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It becomes activated

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It releases cytokines

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These cytokines cause B-cells to become activated and T-killer cells to become activated.

8.

The activated B-cells divide by mitosis to form plasma cells and B-memory cells.

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The activated T-killer cells engulf any infected cells

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They mature in the bone marrow

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They are activated by T-cells (as described above) to produce plasma cells and B-memory cells

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Plasma cells secrete specific antibodies

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B-memory cells remain in low quantities in the body until the same pathogen is encountered again. When this does happen, they divide into plasma cells and secrete antibodies against the pathogen