The group I and group II introns have the remarkable ability to excise themselves from an RNA. This is called auto-splicing, or self-splicing. 

Group I introns are more common than group II introns.

TLS Online TPP Program

#Id: 1773

#Unit 4. Cell Communication and Cell Signaling

Third mechanism for maintaining tolerance, in addition to T-cell anergy and apoptosis, is through the activity of regulatory T cells (TREG cells).

TLS Online TPP Program

#Id: 1774

#Unit 4. Cell Communication and Cell Signaling

TREG can be generated both naturally, in the thymus (nTREG cells), and after induction by antigen in the periphery (iTREG cells).

TLS Online TPP Program

#Id: 1775

#Unit 4. Cell Communication and Cell Signaling

TLS Online TPP Program

#Id: 1776

#Unit 4. Cell Communication and Cell Signaling

In the presence of antigen and TGF-β, CD8+ regulatory T cells expressing FoxP3 can be induced (iTREG).

TLS Online TPP Program

#Id: 1777

#Unit 4. Cell Communication and Cell Signaling

Three main pathways of CD8+ regulatory T cells:

a. APC lysis

b. Inhibition of APC function

c. Regulation of effector T cells

TLS Online TPP Program

#Id: 1778

#Unit 4. Cell Communication and Cell Signaling

TREG cells were most recently characterized as a unique subset of CD4+ T cells that express high levels of the IL-2R  chain (CD25), the low-affinity receptor for this cytokine.