Characterization of a 50 kDa surface membrane protein on thymic stromal cells as an important factor for early T cell development

We previously reported that the nude mouse-derived splenic Tcell clone, N-9F, exhibits a prollferative response to the SL10.3thymic epithelial cell clone. In the present study we generatedan Armenian hamster mAb, HS9, specific for SL10.3, which Inhibitedthe N-9F's proliferative response to SL10.3. We performed thymocyterepopulation experiments using fetal liver cells and 2'-deoxyguanosine-treatedthymic rudiments. After 14 days of culture, donor fetal livercells proliferated and differentiated to CD4⁺CD8⁺ and CD4^–CD8⁺with some CD4⁺CD8^– cells in the host thymic rudiments.However, most of the thymocytes remained at a CD4^–CD8^–immature stage in the presence of HS9 and the cell recoverywas reduced to 30% of the control. Immunohistostaining and flowcytometry studies revealed that HS9 reacted with stromal cellsof fetal thymus at the earliest from day 14 gestation. Neitherthymocytes nor lymph node T cells were stained with HS9. HS9antigen was distributed not only on thymic subcapsular and corticalstromal cells, but also on peripheral B cells in adult mice.The antigen that HS9 detected was found to be a 50 kDa surfacemembrane protein on thymic stromal cells. On the other hand,the 50 kDa molecule is associated with two other molecules of80 and 100 kDa on the B cells. These data indicate that theHS9 antigen may have an important role for early T cell development,especially at a stage from CD4^–CD8^– to CD4⁺CD8⁺,and may have some unknown function on B cells.