Early stages of T cell development are thought to include a series of
coordinated interactions between thymocytes and other cells of the thy
mus. A monoclonal antibody specific for mouse CD81 was identified that
blocked the appearance of alpha beta but nor gamma delta T cells in f
etal organ cultures initiated with day 14.5 thymus lobes. In reaggrega
tion cultures with CD81-transfected fibroblasts, CD4(-)CD8(-) thymocyt
es differentiated into CD4(+)CD8(+) T cells, Thus, interactions betwee
n immature thymocytes and stromal cells expressing CD81 are required a
nd may be sufficient to induce early events associated with T cell dev
elopment.