Termination requires that all hydrogen bonds holding the RNA–DNA hybrid together must be broken, after which the DNA duplex reforms.

TLS Online TPP Program

#Id: 1886

#Unit 4. Cell Communication and Cell Signaling

T-Cell Development

a. Commitment of hematopoietic precursors to the T cell lineage

b. The initiation of antigen receptor gene rearrangements

c.  The selection and expansion of cells that have successfully rearranged one of their T-cell receptor genes (-selection).

TLS Online TPP Program

#Id: 1887

#Unit 4. Cell Communication and Cell Signaling

Time course of appearance of  thymocytes and  thymocytes during mouse fetal development.

TLS Online TPP Program

#Id: 1888

#Unit 4. Cell Communication and Cell Signaling

Allelic exclusion

Most T cells fully rearrange and express a TCR chain from only one of their two TCR alleles

TLS Online TPP Program

#Id: 1889

#Unit 4. Cell Communication and Cell Signaling

Thymic selection

The most distinctive property of the mature T cells is that they recognize only foreign antigen combined with self-MHC molecules.

TLS Online TPP Program

#Id: 1890

#Unit 4. Cell Communication and Cell Signaling

Two distinct selection processes are required:

 • Positive selection, which selects for those thymocytes bearing receptors capable of binding self-MHC molecules, resulting in MHC restriction

• Negative selection, which selects against thymocytes bearing high-affinity receptors for self-MHC/peptide complexes, resulting in self-tolerance.

TLS Online TPP Program

#Id: 1891

#Unit 4. Cell Communication and Cell Signaling

T-cell education