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Updated: Dec 10, 2025

Isolation and Th17 Differentiation of Naïve CD4 T Lymphocytes
Published on: September 26, 2013
Bystander CD4+ T cells: crossroads between innate and adaptive immunity
Hong-Gyun Lee1,2, Min-Ji Cho1,2, Je-Min Choi3,4,5
1Department of Life Science, College of Natural Sciences, Hanyang University, Seoul, Republic of Korea.
T cells can be activated without direct antigen recognition, a process called bystander activation. This innate-like function of T cells is crucial for fighting infections and in autoimmune diseases.
Area of Science:
- Immunology
- Cellular Biology
Background:
- T cells mediate adaptive immunity via specific T-cell receptor (TCR) recognition.
- Antigen-specific immunity and immunological memory are established through clonal selection and expansion.
- TCR-independent 'bystander activation' allows T cells to respond without direct antigen stimulation.
Purpose of the Study:
- To review the mechanisms of TCR-independent bystander activation in CD4+ T cells.
- To explore the physiological roles of bystander-activated T cells in infection, autoimmunity, and cancer.
Main Methods:
- This review synthesizes recent findings on bystander activation.
- Discussion focuses on inflammatory mediators and T cell functions.
Main Results:
- Bystander-activated T cells rapidly secrete effector cytokines.
- Antigen-independent activation highlights a distinct innate-like function of conventional T cells.
- This activation is important in infection clearance and autoimmune pathogenesis.
Conclusions:
- Bystander activation represents a significant immunological function of T cells.
- Understanding these pathways is key to addressing infectious and autoimmune diseases, and cancer immunotherapy.
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