Subtypes of thymic epithelial cells defined by neuroendocrine markers.

The study attempted to define characteristics of thymic epithelial cells within rat thymus based on the expression of neuroendocrine markers. Using an immunohistochemical approach, the following markers were localised: protein gene product 9.5 (PGP 9.5), neuron-specific enolase (NSE) and chromogranin A (ChA). It was shown that cells displaying immunostaining typical for individual markers reside in distinct regions of the thymus and represent subtypes within various populations of thymic epithelial cells. An immunoreactivity for PGP 9.5 was found exclusively in a subtype of cortical epithelial cells, located mostly within the inner zone of the cortex. On the other hand, NSE represented a marker of most epithelial cells located in the medulla. Few such cells which were negative for NSE proved positive for ChA. Among the cells with a strong reaction for NSE some cells also manifested a positive reaction for ChA. While the pattern of neuroendocrine marker distribution may reflect functional properties of thymic epithelial cells which might be different within distinct areas of the thymus, the differential expression of individual markers seems to reflect biological activity of the cells and/or distinct stages of their differentiation.