The discovery of the blood-thymus barrier.

The blood-thymus barrier is a functional and selective barrier separating T-lymphocytes from blood and cortical capillaries in the cortex of the thymus. The existence of this barrier was proposed for the first in time in 1961 by Marshall and White, and demonstrated in 1963 by Clark and Weiss. The most clear morphological evidence concerning the existence of the blood-thymus barrier may be attributed to the collaborative work published in 1972 by two scientists, Morris Karnovsky and Elio Raviola. Raviola and Karnovsky, using peroxidase as a permeability tracer, demonstrated that the venules at the cortico-medullary junction are the site of leakage for blood antigens, while the capillaries draining the cortex are largely impermeable. Other permeability studies have confirmed the existence of a blood-thymus barrier, which allow the access to low molecular weight tracers, while most exclude high molecular weight particles.