PERIPHERAL T-CELLS UNDERGOING SUPERANTIGEN-INDUCED APOPTOSIS IN-VIVO EXPRESS B220 AND UP-REGULATE FAS AND FAS LIGAND

Staphylococcal enterotoxin B (SEB) is a bacterial superantigen (SAg) t hat predominantly interacts with V beta 8(+) T cells. In vivo treatmen t of mice with SEB leads to an initial increase in the percentage of V beta 8(+) T cells, followed by a decrease in the numbers of these cel ls, eventually reaching lower levels than those found before treatment with the SAg. This decrease is due to apoptosis of the SEB-responding cells. In the present study, we use the distinct light scattering cha racteristics of apoptotic cells to characterize T cells that are being deleted in response to SEB in vivo. We show that dying, SEB-reactive T cells express high levels of Fas and Fas Ligand (Fas-L), which are i mplicated in apoptotic cell death. In addition, the B cell marker B220 is upregulated on apoptotic cells. Moreover, we show that the generat ion of cells with an apoptotic phenotype is severely impaired in respo nse to SEB in functional Fas-L-deficient mutant gld mice, confirming t he role of the Fas pathway in SAg-mediated peripheral deletion in vivo .