FAS and toxic epidermal necrolysis: Although the involvement of Fas-FasL interactions in mediating keratinocyte death in SJS/TEN was demonstrated in numerous studies, controversy remains as to whether elevated level of sFasL in the TEN sera results from cleavage of mFasL on the epidermal cells or PBMC, as well as whether TEN keratinocytes express lytically active forms of FasL.