T cell–mediated Fas-induced keratinocyte apoptosis plays a key pathogenetic role in eczematous dermatitis
Axel Trautmann, Mübeccel Akdis, Daniela Kleemann, Frank Altznauer, Hans-Uwe Simon, Thomas Graeve, Michaela Noll, Eva-B. Bröcker, Kurt Blaser, Cezmi A. Akdis
Axel Trautmann, Mübeccel Akdis, Daniela Kleemann, Frank Altznauer, Hans-Uwe Simon, Thomas Graeve, Michaela Noll, Eva-B. Bröcker, Kurt Blaser, Cezmi A. Akdis
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Article

T cell–mediated Fas-induced keratinocyte apoptosis plays a key pathogenetic role in eczematous dermatitis

Abstract

Clinical and histologic similarities between various eczematous disorders point to a common efferent pathway. We demonstrate here that activated T cells infiltrating the skin in atopic dermatitis (AD) and allergic contact dermatitis (ACD) induce keratinocyte (KC) apoptosis. KCs normally express low levels of Fas receptor (FasR) that can be substantially enhanced by the presence of IFN-γ. KCs are rendered susceptible to apoptosis by IFN-γ when FasR numbers reach a threshold of approximately 40,000 per KC. Subsequently, KCs undergo apoptosis induced by anti-FasR mAb’s, soluble Fas ligand, supernatants from activated T cells, or direct contact between T cells and KCs. Apoptotic KCs show typical DNA fragmentation and membrane phosphatidylserine expression. KC apoptosis was demonstrated in situ in lesional skin affected by AD, ACD, and patch tests. Using numerous cytokines and anti-cytokine neutralizing mAb’s, we found no evidence that cytokines other than IFN-γ participate in this process. In addition, apoptosis-inducing pathways other than FasR triggering were ruled out by blocking T cell–induced KC apoptosis by caspase inhibitors and soluble Fas-Fc protein. Responses of normal human skin and cultured skin equivalents to activated T cells demonstrated that KC apoptosis caused by skin-infiltrating T cells is a key event in the pathogenesis of eczematous dermatitis.

Authors

Axel Trautmann, Mübeccel Akdis, Daniela Kleemann, Frank Altznauer, Hans-Uwe Simon, Thomas Graeve, Michaela Noll, Eva-B. Bröcker, Kurt Blaser, Cezmi A. Akdis

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(a) Expression of FasR mRNA by primary human KCs. Lane 1: unprotected te...
(a) Expression of FasR mRNA by primary human KCs. Lane 1: unprotected template. Lane 2: after 8 hours of KC culture. Lane 3: after 24 hours of KC culture. Lane 4: after 16 hours of KC culture followed by 8 hours with 1.0 μg/mL anti-FasR mAb. Lane 5: after 16 hours of KC culture followed by 8 hours with diluted (50%) supernatant (sup.) from stimulated CD45RO+ T cells. Lane 6: after 16 hours of KC culture followed by 8 hours with 1.0 ng/mL IFN-γ. A representative result of three experiments is shown. (b) IFN-γ and Fas-induced KC apoptosis. KC viability was monitored by ethidium bromide exclusion and flow cytometry. Treatments shown are control (KCs alone), 1 μg/mL activating anti-FasR mAb, 10 ng/mL IFN-γ, and 1 μg/mL anti-FasR mAb added 1 day after starting incubation with 10 ng/mL IFN-γ. AP < 0.05. (c) IFN-γ–induced FasR counts exhibit a threshold for KC apoptosis. KCs were pretreated with the indicated doses of IFN-γ; 1 μg/mL anti-FasR mAb was added 1 day after starting incubation with IFN-γ. KC viability was assessed by ethidium bromide exclusion and flow cytometry at day 3. FasR count 1 day after starting incubation with indicated doses of IFN-γ. (d) CD45RO+ T cell–induced KC death is inhibited by blocking IFN-γ. KC viability was monitored by ethidium bromide exclusion and flow cytometry. In the flow cytometry setting, KCs and T cells are gated according to forward and side scatter. Both cell populations were therefore monitored separately. Coculture of primary human KCs and autologous unstimulated or stimulated (with anti-CD2, anti-CD3, and anti-CD28 mAb) CD45RO+ T cells. AP < 0.05. Inhibition of CD45RO+ T cell–induced KC death by 1 μg/mL blocking anti–IFN-γ receptor mAb and 20 μg/mL neutralizing anti–IFN-γ mAb. Results in b–d represent mean ± SD of triplicate cultures from three different experiments. Control, KCs alone.