Blood–thymus barrier

The blood–thymus barrier regulates exchange of substances between the circulatory system and thymus, providing a sequestered environment for immature T cells to develop. The barrier also prevents the immature T cells from contacting foreign antigens (since contact with antigens at this stage will cause the T cells to die by apoptosis).

The barrier is formed by the continuous blood capillaries in the thymic cortex, reinforced by type 1 epithelial reticular cells (sometimes called thymic epithelial cells) and macrophages.

The existence of this barrier was first proposed in 1961 and demonstrated to exist in mice in 1963.^[1]

See also

• Blood–air barrier – Membrane separating alveolar air from blood in lung capillaries
• Blood–brain barrier – Semipermeable capillary border that allows selective passage of blood constituents into the brain
• Blood–ocular barrier – Physical barrier between the local blood vessels and most parts of the eye itself
• Blood–retinal barrier – Part of the blood–ocular barrier that prevents certain substances from entering the retina
• Blood–testis barrier – Physical barrier between the blood vessels and the seminiferous tubules of animal testes