Extracellular matrix-induced stimulation of a CD4-8- thymic T cell line

PBK101 was a thymic T cell line of AKR/J origin that expressed Thy 1, CD44, IL-2R, and VLA-4 antigens but not CD4, CD8, or the TCR/CD3 complex. PBK101 was initially isolated growing together with adherent thymic stromal cells. The proliferation of PBK101 ceased when it was cultured in the absence of stromal cells and its proliferation was stimulated when stromal cells were added back to the culture. PBK101 cells were also stimulated when cocultured with peritoneal exudate cells (PEC). These responses appeared to require contact between PBK101 and the cellular stimulators. The stimulatory activity of the thymic stromal cell line remained in culture wells after the cellular elements were removed by mild trypsinization or detergent extraction indicating that a stimulatory molecule(s) was associated with extracellular matrix (ECM). The activity of the ECM was resistant to high salt extraction, acetic acid, and strong denaturants but was sensitive to treatment with trypsin, heat (80 degrees C), and, if cells were treated with a lathyragen, 4 M guanidine-HCl plus 2 mM dithiothreitol (DTT). The extracellular matrix produced by some other fibroblast cell lines was nonstimulatory. Stimulation of PBK101 by ECM was not inhibited by monoclonal anti-VLA4 or polyclonal anti-fibronectin antisera. Purified extracellular matrix proteins (laminin, collagen, fibronectin, and vitronectin) were either nonstimulatory or only marginally stimulated PBK101 cells. These results suggested that a potentially novel molecule(s) present in the extracellular matrix of a thymic stromal cell line and on the surface of other cellular elements stimulated a thymic T cell line of immature phenotype. The potential role of extracellular matrix-associated molecules in normal T cell development is discussed.