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Background Tumour necrosis factor (TNF)-α blockade using infliximab, a chimeric anti-TNF-α antibody, is an effective treatment for plaque-type psoriasis, inducing remission in about 80% of patients. Objectives To examine infliximab-induced programmed cell death (PCD) of keratinocytes in psoriatic plaques on serial skin biopsy samples. Methods Five patients with moderate to severe plaque-type psoriasis received infliximab infusions intravenously (5 mg kg−1) at weeks 0, 2 and 6. Biopsies of nonlesional and lesional skin (days 0, 5, 14 and 21) were obtained. Conventional microscopy was used to examine the morphology of the psoriatic keratinocytes. In situ detection of apoptosis was performed by electron microscopy and by immunohistochemical staining with anti-p53 and anti-caspase-3 antibodies. Results Infusion of infliximab induced a clinical response in all five patients with psoriasis, with a mean Psoriasis Area and Severity Index improvement of 24·8% already at day 5. This was accompanied by significant histopathological changes in the skin biopsy samples after infliximab treatment. Light and electron microscopic evaluation revealed apoptosis-like morphological changes in lesional keratinocytes, i.e. nuclear condensation, chromatin fragmentation and cytoplasmic vesiculation, visible already after the first infusion. These damaged keratinocytes stained positively for p53, but not for active caspase-3. Conclusions The effects of infliximab in psoriasis extend beyond merely anti-inflammatory actions, and may include caspase-independent PCD of lesional keratinocytes. The PCD of keratinocytes may be an important mechanism that could explain at least in part the rapid and sustained therapeutic effect of infliximab in psoriasis. [ABSTRACT FROM AUTHOR]