Immunology

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importance of antigen presenting cells in the induction of T lymphocyte responses

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T cell mediated immunity is there to: Detect and eliminate pathogens that live

and eliminate altered cells e.g. tumours

Intracellular pathogens require a different strategy to extracellular pathogens. You can't just have a humoral response, you need a

response and this is done by T-cells. Naive T-cells are activated in the secondary lymphoid organs e.g spleen, lymph nodes etc

Lymphocytes recirculate in the blood and lymph nodes via post capillary vessels called

(HEV). Recirculation increases likelihood to encounter an antigen, only effector cells can enter non-lymphoid tissue, which means that

lymphocytes can't. They migrate via diapedesis. The T-cell needs an antigen in order to become an

They also require co-stimulation and are silenced without it. Antigen recognition without co-stimulation leads to tolerance, the T-cell becomes

Activated T-cells can secrete and respond to interleukin typev

(autocrine stimulation). Activation of naive T-cells causes the expression of high affinity IL-2 receptors. IL-2 binds to this and promotes T-cell growth and proliferation

In essence, on recognition of the antigen, the T-cell starts specific proliferation and differentiation and can go on to fulfil its

function. IL-2 also activates T-helper cells, types 1 and 2. These secrete more IL-2 and activate

T-cells.



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