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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...

B Cell Activation and Differentiation

B Cell Activation and Differentiation

The adaptive immune response, a sophisticated defense mechanism, relies on the activation and differentiation of B lymphocytes, or B cells. These processes enable our bodies to mount a tailored response against specific pathogens such as bacteria, free virus particles, toxins, and parasites.
When naive B cells encounter a specific antigen that can bind to the B cell receptor (BCR) on their surface, they undergo sensitization to respond to the antigen's presence. Sensitization begins with...

Antigen Presenting Cells

Antigen Presenting Cells

The immune system is a complex network of cells and molecules that protects the body from foreign invaders. T cells, a type of white blood cell, play a crucial role in this process. They recognize and attack foreign substances, such as pathogens, that enter the body.
T cells require the help of antigen-presenting cells (APCs), which process foreign antigens into smaller fragments that can be recognized by T cells. These APCs are highly specialized cells that efficiently internalize antigens...

T Cell Types and Functions

T Cell Types and Functions

When T cells with CD4 markers are activated, they give rise to two types of effector cells: helper T cells and regulatory T cells. Meanwhile, T cells with CD8 markers differentiate into effector cytotoxic T cells. The differentiation of CD4 T cells into helper T cell subsets, such as Th1, Th2, and Th17 cells, is dependent on the antigen type, antigen-presenting cell, and regulatory cytokines.
Th1 cells stimulate dendritic cells to express necessary co-stimulatory molecules on their surfaces for...

Cell-mediated Immune Responses

Cell-mediated Immune Responses

Antigens Involved in Adaptive Immunity

Antigens Involved in Adaptive Immunity

An antigen is any substance the immune system identifies as foreign and potentially harmful to the body, prompting an immune response. Antigens have two functional properties: immunogenicity and reactivity. Immunogenicity is the ability of an antigen to stimulate a specific immune response. At the same time, reactivity describes the antigen's ability to react with the cells and antibodies produced in response to it.
Complete Antigens
Complete antigens possess both immunogenicity and reactivity.

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Related Experiment Video

Updated: Jun 19, 2026

Induction of Alloantigen-specific Anergy in Human Peripheral Blood Mononuclear Cells by Alloantigen Stimulation with Co-stimulatory Signal Blockade

Induction of Alloantigen-specific Anergy in Human Peripheral Blood Mononuclear Cells by Alloantigen Stimulation with Co-stimulatory Signal Blockade

Published on: March 14, 2011

Dendritic cell function in allostimulation is modulated by C5aR signaling.

Qi Peng¹, Ke Li, Naiyin Wang

¹Complement Laboratory, MRC Centre for Transplantation, King's College London, School of Medicine at Guy's Hospital, London, UK.

Journal of Immunology (Baltimore, Md. : 1950)

|October 30, 2009

Summary

Complement component 5a (C5a) directly activates dendritic cells (DCs) via C5aR, enhancing their T cell stimulation capacity. This involves modulating signaling pathways like PI3K/AKT and NF-kappaB.

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Development and Functional Characterization of Murine Tolerogenic Dendritic Cells

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Last Updated: Jun 19, 2026

Induction of Alloantigen-specific Anergy in Human Peripheral Blood Mononuclear Cells by Alloantigen Stimulation with Co-stimulatory Signal Blockade

Induction of Alloantigen-specific Anergy in Human Peripheral Blood Mononuclear Cells by Alloantigen Stimulation with Co-stimulatory Signal Blockade

Published on: March 14, 2011

Isolation Protocol of Mouse Monocyte-derived Dendritic Cells and Their Subsequent In Vitro Activation with Tumor Immune Complexes

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Published on: May 31, 2018

Development and Functional Characterization of Murine Tolerogenic Dendritic Cells

Development and Functional Characterization of Murine Tolerogenic Dendritic Cells

Published on: May 18, 2018

Area of Science:

Immunology
Complement System
Cellular Signaling

Background:

The role of C5a in regulating T cell immunity is recognized, but its precise mechanisms and cellular targets remain unclear.
Dendritic cells (DCs) are crucial antigen-presenting cells that bridge innate and adaptive immunity, influencing T cell responses.

Purpose of the Study:

To investigate the direct effects of C5a-C5aR interaction on dendritic cell activation and their subsequent T cell stimulatory functions.
To elucidate the specific intracellular signaling pathways involved in C5a-mediated DC modulation.

Main Methods:

Utilized dendritic cells from C5a receptor knockout (C5aR-/-) mice and wild-type DCs treated with a C5aR antagonist.
Assessed DC activation markers (MHC class II, B7.2), cytokine production (IL-10, IL-12p70) following LPS stimulation.
Evaluated T cell stimulation capacity and analyzed intracellular signaling pathways (cAMP, PKA, PI3K/AKT, NF-kappaB).

Main Results:

DCs lacking C5aR or treated with antagonist showed reduced activation, decreased IL-12p70, increased IL-10, and impaired T cell stimulation.
Conversely, C5a stimulation enhanced DC activation, allostimulation capacity, and modulated signaling pathways.
C5aR stimulation inhibited cAMP production and PKA activity while activating PI3K/AKT and NF-kappaB signaling in DCs.

Conclusions:

C5a directly acts on C5aR expressed on DCs, promoting their activation and enhancing their ability to stimulate allospecific T cells.
The observed DC functional enhancement by C5a involves the down-regulation of the cAMP/PKA pathway and up-regulation of PI3K/AKT and NF-kappaB signaling.