The uptake and localization of proteins, Evans Blue and carbon black in the normal and pathological thymus of the guinea-pig.

Radioiodine-labelled homologous serum albumin and heterologous γ-globulin reached the extravascular space of the guinea-pig thymus in concentrations comparable with those in the spleen and in lymph-nodes. The uptake of proteins in a locally X-irradiated involuting thymus gland was approximately doubled at 6, 12, 24 and 48 hours compared with non-irradiated controls. At 7 days the concentration was greater than in the other lymphoid tissues examined, namely spleen, cervical and mesenteric lymph-nodes, and was greater than in control glands by a factor of two to four. Localization of foreign material was studied with Evans Blue and carbon black which were found in macrophages of the capsule, cortex and medulla, and in Hassall's corpuscles. The foreign material showed a marked increase in the parenchyma of glands during involution whether produced by X-irradiation, cortisone or corticotrophin. The significance of these findings in relation to the formation of germinal centres in the thymus in pathological conditions is discussed.