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Related Concept Videos

Development of Immunocompetence01:22

Development of Immunocompetence

The initiation of cell-mediated immunity can be observed as early as the third month of fetal growth, with active antibody-mediated immunity following approximately one month later.
The initial cells that migrate from the fetal thymus settle within the skin and epithelial tissues lining the mouth, digestive tract, and in females, the uterus and vagina. These cells, including skin-based dendritic cells, serve as antigen-presenting cells, playing a key role in T cell activation.
Subsequent T...
Overview of Cell Death01:30

Overview of Cell Death

Cell death is an essential process where the body gets rid of old or damaged cells. Cell proliferation and death need to be balanced, as an imbalance between the two may lead to cancer or autoimmune diseases.
Cell death was observed in the early 19th century, but there was no experimental evidence to prove it. In 1842, Carl Vogt first discovered cell death in a metamorphic toad; however, it was not termed ‘cell death.’ Scientists discovered different cell death pathways only in the 20th century...
The Extrinsic Apoptotic Pathway01:17

The Extrinsic Apoptotic Pathway

The extrinsic apoptotic pathway is initiated when extracellular death-inducing signals, such as specific cytokines, activate the death receptors expressed on the cell surface. The immune cells involved in this pathway are natural killer cells (NK cells) and cytotoxic T-lymphocytes. NK cells are critical in innate immune response, while cytotoxic T-lymphocytes are associated with adaptive immune response. These cells recognize specific receptors expressed on the altered cells and activate...
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...
Regulation of Hematopoietic Stem Cells01:01

Regulation of Hematopoietic Stem Cells

All blood and immune cells are produced from the multipotent hematopoietic stem cells (HSCs) by the process of hematopoiesis. However, they all have a limited life span. In addition, many are depleted in immune surveillance or combatting an injury or infection. This makes blood one of the most regenerative tissues. Hematopoiesis helps replenish these blood and immune cells, restoring the body's normal functioning. However, overproduction of blood and immune cells can make them cancerous or...
T Cell Types and Functions01:24

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...

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Cell death and thymic export during fetal life.

Joanne E Holder1, Elizabeth A Washington, Craig P Cunningham

  • 1Laboratory for Foetal and Neonatal Immunology, Department of Veterinary Science, The University of Melbourne, Parkville, Australia.

European Journal of Immunology
|September 20, 2006
PubMed
Summary

The fetal thymus exports twice as many CD8+ as CD4+ T cells daily, with stricter selection for CD4+ cells. CD8+ T cells migrate to the spleen, while CD4+ T cells distribute randomly.

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Characterization of Thymic Settling Progenitors in the Mouse Embryo Using In Vivo and In Vitro Assays

Published on: June 9, 2015

Area of Science:

  • Immunology
  • Developmental Biology
  • Fetal Physiology

Background:

  • T cell homeostasis mechanisms during fetal development remain largely unknown.
  • The fetal peripheral T cell pool expands significantly with fetal growth.

Purpose of the Study:

  • To elucidate the mechanisms regulating T cell homeostasis in the fetal sheep thymus.
  • To investigate the export dynamics and migration patterns of fetal thymic emigrants.

Main Methods:

  • Quantification of CD4+ and CD8+ thymic emigrants in fetal sheep.
  • Analysis of thymocyte apoptosis and clonal deletion stringency.
  • Tracking of T cell emigrant migration to spleen and lymph nodes (LN).

Main Results:

  • The fetal thymus exports approximately twice as many CD8+ as CD4+ T cells daily.
  • CD4+ thymocyte selection is more stringent, with only 1 in 35 single-positive CD4 (SPCD4) thymocytes exported, versus 2/3 of single-positive CD8 (SPCD8) thymocytes.
  • Apoptotic SPCD4 thymocytes were 40 times more numerous than apoptotic SPCD8 thymocytes.
  • Fetal CD8+ T cell emigrants show spleen-specific localization, unlike CD4+ emigrants which distribute randomly to spleen and LN.

Conclusions:

  • Fetal T cell homeostasis is regulated by differential export rates and selection stringency in the thymus.
  • Distinct migratory patterns of CD4+ and CD8+ T cells are established early in fetal development.
  • These findings provide insight into the establishment of the T cell repertoire during fetal life.