T cell Receptor Excision Circles

(TRECs) in Thymocyte Development

Anna Merca

VIV, SMIFall 2006

Thymocyte Development

• Multipotent precrusor cells from bone marrow develop into αβ or γδ T cells

• Development:

Abbas & Lichtman 2005

Markers in lymphocyte development

Lineages of T-cells

• Dicted by the type of receptors they express, can either be:

αβ or γδ • αβ T cells can have either CD4 or

CD8 co-receptors that specifically recognice MHC class II and MHC class I molecules respectively on antigen presenting cells

Order of T-cell receptor gene re-arrangements:

1.TRD (delta)

2.TRG (gamma)

3.TRB (beta)

4.TRA (alpha)

Lymphocytes migrate into the thymus & start rearranging their T cell receptor (TCR) DNA to make TCRs

Immunobiology 5th edition

Gene Rearrangements• involve the following domains:

– V (variable), D (diversity) and J (joining)

• TRD and TRB:– D to J joining followed by V to DJ joining

• TRA and TRG- V to J joining

TRD & TRA gene rearrangement

Hazenberg et al 2001

TRB gene rearrangement

Hazenberg et al 2001

Double Positive Cells interact with Cortical Epithelial Cells

Immunobiology 5th edition

Double Positive Cell Develops into Single Positive CD8+ T cells

Immunobiology 5th edition

Double Positive Cell Develops into Single Positive CD4+ T cells

Immunobiology 5th edition

- single Positive T cells are subjected to ”negative selection” if their affinity for self antigens is too strong...they undergo apoptosis

- single positive cells that bind too weakly also become subject to ”negative selection” and consequently undergo apoptosis

- remaining cells become mature naive T-cells that migrate out of the thymus into the priphery

Negative Selection and Maturation of Naive T-cells

TCRβ expCD 34 exp

34+1a- 34+1a+ 34+4+ 34-4+ 4+8α+ β- 8β+3-

γδ TCR+

αβTCR

CD8 SP

CD4 SP

γδ potential

β selection

Model of Human αβ and γδ Thymocyte development

Hazenberg et al 2001

Ways to quantify TRECs

• Through several PCR-based methods like:

– competitive PCR

– PCR–ELISA or

– RQPCR

Factors affecting TREC content

Hazenberg et al 2001