Blood–thymus barrier
Appearance
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 epithelial reticular cells and macrophages.