T cells develop in the thymus The size of thymus is gradually decreased from the birth, and rapidly reduced from puberty Thus, whole T cell repertoire is decreasing with aging Thymus, T cell and Aging 3days70 years
Signal Transduction Negative Selection TCR signal Death by Neglect Positive Selection About 98% of thymocytes die by apoptosis for their failure in making productive TcR gene rearrangement or failure in receiving survival signal (adequate TcR signal)
Notch 4 isotypes in vertebrate: Notch 1~4 Single-pass receptor Ligands: Delta (-like), Serrate (Jagged) Required for early development of thymocytes Intracellular domain of Notch (Notch-IC) delivers the signal
alpha:beta vs gamma:delta T cells gamma:delta T cells are responsible for about 5% of total peripheral T cells gamma:delta T cells are involved in innate immunity Rearrangement of TcR gamma and delta precedes that of TcR beta
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