Location of FTS (facteur thymique sérique) in the thymus of normal and auto-immune mice.

This study was concerned with the in situ localization of facteur thymique sérique (FTS) by immunoelectron microscopy in the thymus of normal C57BL mice and aged auto-immune SWAN mice. Normal young mice have anti-FTS antibodies fixed specifically on the floccular material present in the cytoplasmic vacuoles of epithelial cortical and medullary cells. In aged auto-immune SWAN mice the anti-FTS antibodies show an activity only in the granules present in the vacuoles or free in the cytoplasm of epithelial cells. The floccular material is not labelled by the same antibodies. FTS positive granules show a repetitive structure which is characteristic of crystalline protein formations. The presence of FTS in the granules of cells confirm the hypothesis of FTS storage in the cytoplasm of epithelial cells in vivo during the auto-immune process.