Apoptosis of single keratinocytes (KC) is a characteristic feature of spongiosis formation, the histopathologic hallmark of acute eczematous dermatitis. In acute eczema, activated dermis-infiltrating T cells secrete several proinflammatory cytokines which might be decisive for KC apoptosis or survival. We analyzed the role of tumor necrosis factor alpha (TNF-α) in the determination of KC fate during spongiosis formation in acute eczematous dermatitis. Supernatants of activated human CD4⁺ T cells induced apoptosis in primary KC, which could be fully inhibited by individual blockade of interferon-γ (IFN-γ) and CD95 but not by neutralization of TNF-α activity. As compared to CD95-triggering alone, synchronous CD95 and TNF receptor cross-linking in the presence of IFN-γ only marginally enhanced KC apoptosis. Importantly, pre-treatment of KC with TNF-α followed by CD95 stimulation, but not vice versa, significantly amplified KC apoptosis as compared to CD95 stimulation alone. This TNF-α-mediated sensitization to CD95-induced KC cell death could be abrogated by blocking TNF receptor 1 (TNF-R1) but not TNF-R2 mAb. In eczematous dermatitis, the CD95 receptor was expressed throughout the epidermis, whereas immunohistological detection of TNF-R1 was rather restricted to KC around spongiotic vesicle formation. Thus, TNF-α primes KC for CD95-mediated signals which results in an increased susceptibility to apoptosis. TNF-R1 expression and spatial action of TNF-α restricted to spongiotic vesicles promote both CD95-induced KC apoptosis and limitation of spreading KC damage.