CD94/NKG2C is a killer effector molecule in patients with Stevens-Johnson syndrome and toxic epidermal necrolysis

Background

Toxic epidermal necrolysis (TEN) and Stevens-Johnson syndrome (SJS) are severe, bullous cutaneous diseases with uncertain pathogenesis, although cytotoxic T cells seem to be involved. Natural killer (NK)–like activity has been found in blister infiltrates. Cytotoxic T lymphocytes (CTLs) with NK-like activity (NK-CTLs) have been shown to express T-cell receptors restricted by the HLA-Ib molecule HLA-E. Alternatively, the HLA-E–specific activating receptor CD94/NKG2C can trigger T-cell receptor–independent cytotoxicity in CTLs.

Objective

Our aim was to test whether HLA-E expression sensitizes keratinocytes to killing by CTLs with NK-like activity and to explore the expression of activating receptors specific for HLA-E in blister cytotoxic lymphocytes.

Methods

We used flow cytometry and immunohistochemistry to analyze HLA-E expression in keratinocytes from affected skin in patients with SJS, TEN, and other less severe drug-induced exanthemas. The expression of CD94/NKG2C was analyzed by means of flow cytometry in PBMCs and blister cells from patients. PBMCs and blister cells were analyzed for their ability to kill HLA-E–expressing cells. Involvement of CD94/NKG2C in triggering degranulation of cytolytic cells was explored by means of CD107a mobilization assays and standard cytotoxicity chromium release assays.

Results

We found that keratinocytes from affected skin expressed HLA-E and that cell-surface HLA-E sensitizes keratinocytes to killing by CD94/NKG2C⁺ CTLs. Frequencies of CD94/NKG2C⁺ peripheral blood T and NK cells were increased in patients with SJS and TEN during the acute phase. Moreover, activated blister T and NK lymphocytes expressed CD94/NKG2C and were able to degranulate in response to HLA-E⁺ cells in an NKG2C-dependent manner.

Conclusion

CD94/NKG2C might be involved in triggering cytotoxic lymphocytes in patients with SJS and TEN.

Key words: Stevens-Johnson syndrome, toxic epidermal necrolysis, drug allergy, NK-CTLs, CD94/NKG2C, HLA-E

Abbreviations used: BFC, Blister fluid cell, CTL, Cytotoxic T lymphocyte, FasL, Fas ligand, FITC, Fluorescein isothiocyanate, KIR, Killer immunoglobulin-like receptor, MPE, Maculopapular exanthema, NK, Natural killer, NKR, Natural killer receptor, PE, Phycoerythrin, rh, Recombinant human, SJS, Stevens-Johnson syndrome, TCR, T-cell receptor, TEN, Toxic epidermal necrolysis