Immunolocalization of thymosin alpha 1, thymopoietin and thymulin in mouse thymic epithelial cells at different stages of culture: a light and electron microscopic study.

The secretory evolution of the thymic hormones (thymulin, thymosin alpha 1 and thymopoietin) in cultured thymic reticuloepithelial cells (TREC) was studied by immunocytochemical techniques using monoclonal anti-thymulin or anti-thymosin alpha 1 and polyclonal anti-thymopoietin antibodies (Ab). The culture of TREC was performed with a medium where L-valine was replaced by D-valine, thus ensuring rapid and selective development of these cells. The number of thymulin, thymosin alpha 1 or thymopoietin-containing cells increased progressively from Day 6 to Day 12 of the culture. The localization of the three thymic hormones within the TREC also varied according to the age of the culture. By light microscopy the staining of the three hormones was localized in some cytoplasmic granules at the beginning of the culture and at Day 90, while at Day 12 it was throughout the cytoplasm. In electron microscopy these localizations corresponded respectively to vacuoles of different sizes and to cytosol. All these results show that the synthesis and excretion of thymulin, thymosin alpha 1 and thymopoietin evolve during the development of TREC in culture.