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Related Concept Videos

T Cell Activation and Clonal Selection01:22

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...
Primary Lymphoid Organs01:16

Primary Lymphoid Organs

Primary lymphoid organs are pivotal in the formation, development, and maturation of lymphocytes, the white blood cells that serve as the backbone of our immune system. This crucial function underscores their fundamental role in maintaining our overall health and immunity. The two primary lymphoid organs of prime importance are the red bone marrow and the thymus.
The red bone marrow is a soft, spongy tissue nestled in the interior of long bones such as the humerus and femur. It is the site...
Frequency-dependent Selection01:21

Frequency-dependent Selection

When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.Positive Frequency-Dependent SelectionIn positive...
B Cell Activation and Differentiation01:24

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...
Cells of the Adaptive Immune Response01:23

Cells of the Adaptive Immune Response

The T and B lymphocytes of the adaptive immune system develop from common lymphoid progenitor cells in the bone marrow. These progenitors give rise to precursors that eventually develop into both T and B lymphocytes. As these precursors mature, they gain the ability to detect and respond to foreign antigens in the body, a process known as immunocompetence. Additionally, these precursors acquire self-tolerance, a process that ensures they do not react to self-antigens. This intricate system...
Special Features of Adaptive Immunity01:20

Special Features of Adaptive Immunity

The adaptive immune system, a crucial component of the overall immune response, offers a highly specialized defense against pathogens. It involves specific cell types and features, enabling it to combat infections effectively and efficiently.
The primary cell types involved in adaptive immunity are T cells and B cells. Each type has a unique role in defending the body against pathogens. T cells are responsible for cell-mediated immunity. They identify and eliminate infected cells directly,...

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Related Experiment Video

Updated: Jun 22, 2026

Preparation and Applications of Organotypic Thymic Slice Cultures
10:10

Preparation and Applications of Organotypic Thymic Slice Cultures

Published on: August 6, 2016

Why does the thymus involute? A selection-based hypothesis.

Mark R Dowling1, Philip D Hodgkin

  • 1Immunology Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3050, Australia.

Trends in Immunology
|June 23, 2009
PubMed
Summary
This summary is machine-generated.

Thymic involution, the shrinking of the thymus, may have evolved to refine the T-cell repertoire for fighting infections and self-tolerance. Age-related immune decline could be a side effect of this crucial selection process.

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Examination of Thymic Positive and Negative Selection by Flow Cytometry
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Examination of Thymic Positive and Negative Selection by Flow Cytometry

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Isolation and Transplantation of Different Aged Murine Thymic Grafts.
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Isolation and Transplantation of Different Aged Murine Thymic Grafts.

Published on: May 13, 2015

Related Experiment Videos

Last Updated: Jun 22, 2026

Preparation and Applications of Organotypic Thymic Slice Cultures
10:10

Preparation and Applications of Organotypic Thymic Slice Cultures

Published on: August 6, 2016

Examination of Thymic Positive and Negative Selection by Flow Cytometry
14:29

Examination of Thymic Positive and Negative Selection by Flow Cytometry

Published on: October 8, 2012

Isolation and Transplantation of Different Aged Murine Thymic Grafts.
05:47

Isolation and Transplantation of Different Aged Murine Thymic Grafts.

Published on: May 13, 2015

Area of Science:

  • Immunology
  • T-cell biology
  • Aging research

Background:

  • Thymic involution, the age-related decrease in thymus size and function, is a fundamental puzzle in immunology.
  • The thymus is critical for T-cell development and establishing immune tolerance.

Purpose of the Study:

  • To propose a novel evolutionary explanation for thymic involution.
  • To reframe age-associated immune decline as a potential consequence of a beneficial selection process.

Main Methods:

  • This study presents a theoretical argument based on existing immunological principles.
  • It integrates concepts of T-cell repertoire selection and peripheral homeostasis.

Main Results:

  • The study posits that thymic involution evolved to facilitate peripheral selection of T-cells in young adulthood.
  • This selection optimizes the T-cell repertoire for pathogen defense and self-tolerance.

Conclusions:

  • Thymic involution may be an adaptive process, not merely a decline.
  • Understanding T-cell homeostasis in the periphery is key to unraveling thymic involution and immune aging.