Glucocorticoid production in the chicken bursa and thymus

Glucocorticoid (GC) hormones play an important role in thymic T cell select ion and in the development of autoimmune diseases. Previous studies have sh own that the mammalian thymus itself is able to produce GC, In order to ass ess the importance of these findings in terms of the evolutionary developme nt of the immune system, we investigated the functional presence of steroid ogenic enzymes in primary lymphoid organs of chickens, which represent one of the best studied non-mammalian species. To this end, we attempted to dem onstrate enzyme activities of the whole set of steroidogenic enzymes for th e synthesis of GC in the bursa of Fabricius and the thymus, We isolated ste roidogenic organelles from primary lymphoid tissues, incubated these with r adioactive (precursor) steroids in vitro and visualized the resulting produ cts by thin-layer chromatography. Our results show that the chicken bursa a s well as the chicken thymus possesses all enzymes end cofactors required f or GC production, The observation of GC production in an organ responsible for a cell selection and maturation is a further step in uncovering the yet ill-defined mechanism of a cell selection. These results provide the bioch emical basis for the in situ hormonal effects, and underline the general im portance of GC hormones on T and a lymphocyte development and selection.