A novel cytokine-responsive cell surface glycoprotein defines a subset of medullary thymic epithelium in situ.

A hamster mAb (10.1.1), raised against long term cultures of uncloned thymic stromal cells, selectively labeled a subpopulation of medullary stromal cells in situ. By ultrastructural and phenotypic criteria, the stromal cells labeled by this mAb were judged to be epithelial. Although some of the 10.1.1+ epithelial cells were reticular, others were globular and some were associated with structures resembling Hassal's bodies. Ultrastructural immunohistochemistry suggested that 10.1.1 labeling of some of the epithelial cells was preferentially associated at areas of epithelial cell contact with adjacent thymocytes. Reactivity of thymic stromal cells with this antibody was developmentally regulated. A few scattered 10.1.1+ cells were observed at day 14 of gestation, and there were progressive increases in both the extent and intensity of 10.1.1 labeling evident through birth. One thymic stromal cell line, Z210.1, exhibited low levels of constitutive reactivity with this antibody. Exposure to IL-1 resulted in enhanced 10.1.1 reactivity of this cell line, with little, if any, additional response to TNF-alpha or IFN-gamma. Under the same conditions, ICAM-1 expression by this cell line was elevated in response to IL-1, TNF-alpha, or INF-gamma. Immunoprecipitation of detergent lysates prepared from Z210.1.7 cells exposed to IL-1 24 h before cell surface iodination identified a cell surface protein with a molecular mass of about 92 kDa under nonreducing conditions and about 95 kDa under reducing conditions. Digestion of 10.1.1 immunoprecipitates with N-glyconase resulted in a small (5 kDa) reduction in molecular mass. The molecule recognized by the 10.1.1 mAb was distinct from ICAM-1, which possessed a molecular mass of 100 kDa (nonreduced) and 110 kDa (reduced), and also displayed a smaller N-glyconase-resistant molecular mass (65 to 85 kDa).