Cellular and matrix interactions during the development of T lymphocytes

The thymus contains an extensive extracellular matrix. Although thymocytes express integrins capable of binding to matrix molecules, the functional si gnificance of the matrix for T cell development is uncertain. We have shown that the matrix is associated with thymic fibroblasts which are required f or the CD44(+) CD25(+) stage of double negative (CD4(-)8(-)) thymocyte deve lopment. The survival of cells at this stage is dependent on IL-7 and we pr opose that the role of fibroblasts is to present, via the matrix, IL-7 to d eveloping T cells.