Glucocorticoid production in the chicken bursa and thymus

Glucocorticoid (GC) hormones play an important role in thymic T cell selection and in the development of autoimmune diseases. Previous studies have shown that the mammalian thymus itself is able to produce GC. In order to assess the importance of these findings in terms of the evolutionary development of the immune system, we investigated the functional presence of steroidogenic enzymes in primary lymphoid organs of chickens, which represent one of the best studied non-mammalian species. To this end, we attempted to demonstrate enzyme activities of the whole set of steroidogenic enzymes for the synthesis of GC in the bursa of Fabricius and the thymus. We isolated steroidogenic organelles from primary lymphoid tissues, incubated these with radioactive (precursor) steroids in vitro and visualized the resulting products by thin-layer chromatography. Our results show that the chicken bursa as well as the chicken thymus possesses all enzymes and cofactors required for GC production. The observation of GC production in an organ responsible for B cell selection and maturation is a further step in uncovering the yet ill-defined mechanism of B cell selection. These results provide the biochemical basis for the in situ hormonal effects, and underline the general importance of GC hormones on T and B lymphocyte development and selection.