Toxic epidermal necrolysis (TEN) and drug-induced hypersensitivity syndrome (DIHS) represent two ends of a spectrum of severe drug eruptions: DIHS is unique in that severe epidermal damage seen in TEN is absent, sequential reactivations of herpesviruses occur, and autoimmunity often ensues. To investigate whether changes in regulatory T (Treg) cell function would contribute to variability in the clinical manifestations, we examined the frequency, phenotype, and function of Treg cells both during the acute stage and again long after clinical resolution of both diseases. Dramatic expansions of functional Treg cells were found in the acute stage of DIHS. In contrast, Treg function was profoundly impaired in TEN, although present in normal frequency. Skin homing addressins were more preferentially expressed on Treg cells in DIHS than in TEN. Indeed, Treg cells were more abundantly present in the skin lesions of DIHS. Surprisingly, Treg cells contracted upon resolution of DIHS became functionally deficient, whereas their functional defects in TEN were restored upon recovery. These findings indicate that a transitory impairment in their function during the acute stage of TEN may be related to severe epidermal damage, while a gradual loss of their function after resolution of DIHS may increase the risk of subsequently developing autoimmune disease.

Effector-memory T cells are strategically placed to epithelial tissues to provide frontline immune protection against pathogens. Their detrimental effects, however, have been rarely examined because of difficulty in sampling these T cells in pathological settings. Our previous studies suggested persistence of a similar subset of intraepidermal CD8(+) T cells at high frequencies in the lesions of fixed drug eruption, a localized variant of drug-induced dermatoses. In situ activation of this subset resulting in localized epidermal injury can be traced in the lesions after antigen challenge by paired immunohistochemical staining, reverse transcriptase-polymerase chain reaction in situ, and flow cytometry of dispersed cells. Here we show that effector-memory T cells were greatly enriched in these intraepidermal CD8(+) T cells, but not dermal and circulating counterparts, and that they constitutively express an early activation marker CD69 even before challenge. Surprisingly, a large proportion of these T cells expressed immediate effector function as evidenced by the rapid production of high levels of interferon-gamma in situ with much faster kinetics than their counterparts at the mRNA and protein levels after challenge. This was followed by localized epidermal injury. The intracellular cytokine assay ex vivo shows that the great majority of these dispersed T cells produce interferon-gamma. This study provides the first in situ description of the detrimental effects specifically mediated by effector-memory T cells residing at the effector site of immunopathology.

Whether Tregs could migrate to the lesions upon activation of intraepidermal CD8+ T cells would determine whether the inflammation becomes resolved spontaneously or progresses to TEN.

We previously showed that skin-homing CD4 T cells in peripheral blood can be subdivided into three populations on the basis of the expression pattern of the cutaneous lymphocyte Ag (CLA) and fucosyltransferase VII (FucT-VII): FucT-VII+CLA−, FucT-VII+CLA+, and FucT-VII−CLA+. In view of the known late appearance of CLA during T cell differentiation, T cells programmed to attain skin-homing properties may start to generate E-selectin-binding epitopes at early stages of differentiation before induction of CLA expression. To this end, the in vitro differentiation from naive to CLA+ memory T cells was followed after activation with anti-CD3 mAb. Here we demonstrate that naive skin-homing CD4 T cell precursors undergo a linear differentiation process from the FucT-VII+CLA− phenotype to the FucT-VII+CLA+ phenotype and eventually to the FucT-VII−CLA+ phenotype. The appearance of the FucT-VII+CLA− subset coincided with or could be immediately followed by the generation of E-selectin binding epitopes, and even after E-selectin-binding epitopes were no longer detectable, CLA remained expressed for prolonged periods of time, suggesting that induction of functional E-selectin ligands depends primarily on the expression of FucT-VII, but not CLA. Immunofluorescence and confocal microscopy studies of these T cells confirm that most E-selectin ligands were found independently of CLA expression.

Immunohistochemical detection of VZV gE in eccrine epithelium can be a subtle clue to the diagnosis of HZ which displays most unusual manifestations, and VZV-related disorders.