Changes

[[Image:TCR2.jpg|thumb|right|300px|T-cell receptor binds antigen fragments presented by MHC on the cell surface - B. Catchpole, RVC 2008]]

[[Image:TCR2.jpg|thumb|right|300px|T-cell receptor binds antigen fragments presented by MHC on the cell surface - B. Catchpole, RVC 2008]]

Also known as '''T lymphocytes

Also known as '''T lymphocytes

==Introduction==

==Introduction==

<p>T cells are so named as they differentiate in the [[Thymus - Anatomy & Physiology|thymus]]. They are long lived and are involved in ''cell mediated immunity''. They represent 60-80% of the circulating lymphocytes and all express the markers CD2, CD3 and CD7 as well as having T cell receptors (TCR). Each T cell has 30,000 TCRs each of which is identical and recognises antigens and MHC II.</p><p>Functionally they are divided into three subsets that are distinguished by presence or absence of CD4 or CD8 markers. CD4 and CD8 cells have α/β antigen receptors while the γδ cells have the γ/δ antigens receptors.</p>

<p>T cells are so named as they differentiate in the [[Thymus - Anatomy & Physiology|thymus]]. They are long lived and are involved in '''cell mediated immunity'''. They represent 60-80% of the circulating lymphocytes and all express the markers CD2, CD3 and CD7 as well as having T cell receptors (TCR). Each T cell has 30,000 TCRs each of which is identical and recognises antigens and MHC II.</p><p>Functionally they are divided into three subsets that are distinguished by presence or absence of CD4 or CD8 markers. CD4 and CD8 cells have α/β antigen receptors while the γδ cells have the γ/δ antigens receptors.</p>

* T-cell receptors are the antigen-specific receptors for T-lymphocytes

* T-cell receptors are the antigen-specific receptors for T-lymphocytes

* T-cell receptors are a combination of either &alpha;&beta; chains or &gamma;&delta; chains

* T-cell receptors are a combination of either &alpha;&beta; chains or &gamma;&delta; chains

* Like antibody, TCR consist of a distal domain and a membrane proximal constant domain

* Like antibody, TCR consist of a distal domain and a membrane proximal constant domain

** Structurally, they look like a single arm of an antibody molecule

** Structurally, they look like a single arm of an antibody molecule

==Helper CD4+==

==Helper CD4+==