S-100 antigen-positive folliculostellate cells are not the source of IL-6 gene expression in human pituitary adenomas

We have investigated the expression of IL-6 in a random selection of 27 human pituitary adenomas, comprising 8 somatotroph, 5 corticotroph, 3 mammotroph and 11 endocrinologically inactive adenomas, using a 35S-labelled 1.1kb riboprobe complementary to human IL-6. Positive and negative IL-6 transcript controls were generated from the IL-6-secreting human bladder carcinoma cell line T24/83. Tissue from a malignant melanoma was used as a positive S-100 immunocytochemical control tissue. Of the 27 human pituitary adenomas examined by in situ hybridization, 7 (26%) contained IL-6 transcripts: these were 3 of 5 corticotroph adenomas, 2 of 8 somatotrophinomas and 2 of 11 endocrinologically inactive adenomas. In each case, IL-6 transcript-positive cells constituted less than 1% of the total pituitary tissue mass examined. Alternate wax embedded 3 microns thick sections from 5 of the 7 IL-6 transcript positive tumours were examined immunocytochemically for S-100 antigen, or by in situ hybridization for IL-6 transcripts. Immunocytochemistry for S-100 antigen was completely negative in 3 of the 5 tumours and in the remaining 2, there was no evidence of IL-6 transcripts and S-100 antigen co-localization in any of the sections examined. This suggests that in pituitary adenomas, cells other than classical folliculostellate cells are responsible for IL-6 production.