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Evidence for a blood-thymus barrier using electron-opaque tracers
The Journal of Experimental Medicine
|September 1, 1972
Summary
A blood-thymus barrier limits macromolecule entry to the thymus cortex, preventing widespread distribution. While some substances enter the medulla, the cortex remains protected, ensuring immune cell development.
Area of Science:
- Immunology
- Vascular Biology
- Cell Biology
Background:
- The thymus is crucial for T-cell maturation.
- Understanding the blood-thymus barrier is vital for immune regulation.
Purpose of the Study:
- To investigate the permeability of thymus vasculature to macromolecules.
- To determine the existence and location of a blood-thymus barrier.
Main Methods:
- Utilized electron-opaque tracers of varying molecular sizes in young adult mice.
- Analyzed tracer distribution within the thymus using electron microscopy.
Main Results:
- Blood-borne macromolecules penetrate the thymus but are confined to the medulla.
- Cortical capillaries exhibit impermeable endothelial junctions, blocking most tracers.
- Medullary vessels (postcapillary venules, arterioles) are more permeable, allowing tracer entry.
- Macrophages sequester tracers in the cortex, preventing access to lymphocytes.
Conclusions:
- A functional blood-thymus barrier exists, primarily protecting the cortex.
- Medullary lymphocytes are exposed to circulating substances, unlike cortical lymphocytes.