Tissue-specific expression of 11β-HSD1 is an autocrine determinant of cortisol levels in fibroblasts. Results are shown for cultures of dermal (DF), and bone marrow (BF) and synovial fibroblasts (SF). (a) Reductase activity determined by scanning thin layer chromatography (3H-cortisone to 3H-cortisol conversion, 12-hour incubation) following treatment with IL-1 (10 ng/ml, 24 hours) or vehicle. (b) Accumulation of cortisol in cell culture medium (as determined by specific ELISA) from 100 nmol/l cortisone following treatment with TNF-α (10 ng/ml, 24 hours) or vehicle. Values are expressed as mean ± standard deviation of four replicates from a representative culture of RA fibroblasts. Similar values were obtained when the assays were carried out using two other fibroblast cells lines. *P < 0.01, **P < 0.001 versus vehicle-treated cells; #P < 0.01 versus equivalent bone marrow fibroblasts; &P < 0.01 versus equivalent dermal fibroblasts. ELISA, enzyme-linked immunosorbent assay; IL, interleukin; TNF, tumour necrosis factor; u.d., undetectable.