Immunohistochemical localization of interleukin-6 in peripheral human endocrine glands

Interleukin-6 (IL-6) is a pleiotropic cytokine with differentiation and growth-promoting effects. Extensive studies in experimental animals denote that IL-6 is produced in various endocrine organs and participates in the local control of endocrine cell function. The expression of this cytokine in human endocrine glands, however, has only been examined in a limited number of studies. We investigated the immunohistochemical expression and localization of IL-6 in a variety of peripheral human endocrine glands. In the adrenals, IL-6 immunoreactivity was detected in all three zones of the cortex. The reticularis and glomerulosa zones were more heavily stained as compared with the slight immunoreactivity of the fasciculata zone. In the adrenal medulla, chromaffin and sustentacular cells were variably positive. A substantial number of follicular thyroid cells were strongly immunoreactive for IL-6 in all normal and hyperplastic thyroids examined. Parafollicular cells were negative. Parathyroid chief cells were mildly positive; selective and more intense staining was observed in acidophilic cells. Pancreatic islet cells were variably positive. In the testis positive staining was selectively observed in both Leydig and Sertoli cells. In conclusion, IL-6 immunoreactivity is present in almost all the human endocrine glands and it expressed in a cell-specific manner. These observations provide further support for the existence of local immune-endocrine interactions.