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T Cell Activation and Clonal Selection

T Cell Activation and Clonal Selection

T cells are integral to our adaptive immune system, recognizing and effectively responding to foreign antigens. T cell activation and clonal selection are pivotal in orchestrating this immune response. This article elucidates these mechanisms, detailing the roles of cluster of differentiation (CD) markers, major histocompatibility complex (MHC) molecules, costimulatory signals, and the process of clonal selection.
Naive T cells that have not yet encountered an antigen express two primary CD...

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Related Experiment Video

Updated: Jul 29, 2025

In Vivo Augmentation of Gut-Homing Regulatory T Cell Induction

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Published on: January 22, 2020

Transit Amplifying Cells (TACs): a still not fully understood cell population.

Ranieri Cancedda¹, Maddalena Mastrogiacomo²

¹Emeritus Professor, Università degli Studi di Genova, Genoa, Italy.

Frontiers in Bioengineering and Biotechnology

|May 25, 2023

Summary

This summary is machine-generated.

Adult stem cells (SCs) generate transit-amplifying cells (TACs) that are crucial for tissue development and regeneration. These TACs regulate SCs and their progeny, with common molecular pathways like Wnt and Notch across different tissues.

Keywords:

cell dedifferentiation cell reprogramming cultured cells hair follicle intestinal crypt stem cells tissue differentiation tissue regeneration

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Area of Science:

Cell Biology
Developmental Biology
Regenerative Medicine

Background:

Adult stem cells (SCs) maintain tissue homeostasis and regeneration by proliferating slowly in niches.
During development and regeneration, SCs produce highly proliferative transit-amplifying cells (TACs).
TACs are not just a transitional phase but actively regulate SCs and their differentiated progeny.

Purpose of the Study:

To review the generation and function of TACs in high-turnover lining epithelia (epidermis, hair follicles, ocular surfaces, intestinal mucosa).
To compare TAC roles and molecular pathways across different epithelial tissues.
To discuss cultured mesodermal cells (mesenchymal stem cells, dedifferentiated chondrocytes) and their potential reversion to a TAC stage.

Main Methods:

Literature review focusing on TACs in epithelial development and regeneration.
Comparative analysis of TACs across epidermis, hair follicles, ocular surfaces, and intestinal mucosa.
Discussion of common and tissue-specific molecular pathways (Wnt, Notch, Hedgehog, BMP) in TACs.
Exploration of cultured mesenchymal stem cells and dedifferentiated chondrocytes in relation to TACs.

Main Results:

TACs play a critical role in controlling stem cell populations and directing differentiation in various tissues.
Common molecular pathways (Wnt, Notch, Hedgehog, BMP) are involved in TAC regulation, but their responses vary by tissue.
TACs are crucial for the development and regeneration of high-turnover epithelial tissues.
Dedifferentiated cells in culture may revert to a TAC-like state, relevant for cell therapy.

Conclusions:

TACs are essential regulators of tissue development, regeneration, and homeostasis across diverse epithelial systems.
Understanding TACs and their molecular signaling provides insights into regenerative processes and cell therapy.
The potential for dedifferentiated cells to act as TACs warrants further investigation for therapeutic applications.