The neural and neuro-endocrine component of the human thymus. I. Nerve-like structures.

The presence of nerve-like fibers in the human thymus was studied by immunohistochemistry on frozen tissue sections and sections of formalin-fixed paraffin-embedded tissue, for neurofilaments (Nf) of 68-, 160-, and 200-kDa (neuron-specific structural proteins), neuron-specific protein PGP9.5, tyrosin hydroxylase (noradrenergic innervation), chromogranin A (CHROM), synaptophysin (SYN), and the pituitary hormones follicle-stimulating hormone (FSH) and its beta-subunit, growth hormone, adrenocorticotropic hormone, luteinizing hormone, prolactin, beta-subunit of thyroid-stimulating hormone, and somatostatin. Noradrenergic profile-like immunoreactivity was observed in the medulla: immunolabeling was observed also for epithelial cells surrounding Hassall's corpuscles. For neurofilaments, only Nf 160-kDa immunoreactivity was observed in the thymic parenchyma, mainly in long-sized labeling patterns in the medulla. PGP9.5 immunolabeling occurred especially in the cortex, in dendritic labeling patterns compatible with the epithelial network at this location. The medulla showed PGP9.5 immunoreactivity in fiber-like patterns and in large-sized epithelial cells surrounding Hassall's corpuscles. Immunoreactive CHROM was seen in profile-like structures in the subcapsule, cortex, and medulla. SYN immunolabeling occurred focally around Hassall's corpuscles. Profile-like structures immunoreactive for pituitary hormones were observed in the medulla and in less density in the cortex. For FSH the highest density occurred in the cortex, where long-sized profile-like structures were present running over and in between cells, especially in the keratin-positive epithelial dendritic network (two-color immunohistochemistry).