Thrombospondin Functions as a Cytoadhesion Molecule for Human Hematopoietic Progenitor Cells

We explored the role that thrombospondin (TSP). a multifunctional extracellular matrix protein, plays in hematopoietic cell-cell and cell-matrix interactions. Thrombospondin synthesis is differentially regulated in human long-term bone marrow cultures. Consistent with this, human hematopoietic progenitor cells of all three lineages (erythrocyte, megakaryocyte, and granulocyte) use TSP as an attachment protein. However, terminally differentiated cells (erythrocytes and neutrophils) show absent or reduced attachment to TSP. The region within the TSP molecule that mediates cell attachment (cell binding do-