Neuropeptide-immunoreactive cells in human thymus.

The outer cortex of the human thymus contains a one- to two-cell-thick layer that is immunoreactive with antisera against beta-endorphin, (Leu)- and (Met)-enkephalin, bombesin, and substance P. The epithelial nature of these immunostained cells is revealed by immunoelectron microscopic studies showing the presence of desmosomal junctions. The presence of peptide-containing cells in the outer cortex, where the most immature and recently immigrated thymocytes are found, emphasizes the role of neuropeptides in regulating the microenvironment for T cell development.