The role of mesenchyme in thymus development.

We have reviewed the evidence that thymic mesenchymal cells and their progeny thymic fibroblasts play an important role in early T-cell development. Although it is possible that mesenchyme plays an inductive role in thymic epithelial morphogenesis, we have presented evidence to suggest that there is a direct effect of mesenchyme and fibroblasts on T-cell development. Moreover the association of these cell types with an ECM raises the possibility that the latter might be important in integrin and/or cytokine presentation especially during the CD4(-)8- phase of T-cell development.