Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL): a possible pathogenic role in chronic plaque psoriasis.

Background: Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytokine member of the tumour necrosis factor (TNF) family. Its role has been investigated in skin cancers and some inflammatory and/or immune-mediated skin diseases. An involvement of TRAIL in psoriasis pathogenesis has recently been hypothesized. We investigated the expression and localization of TRAIL and its receptors in psoriatic skin and measured serum TRAIL. The intracellular pathways activated by TRAIL were assessed to investigate its potential role in the pathogenesis of psoriasis.
Methods: Twenty-four consecutive patients with plaque psoriasis and age- and sex-matched healthy subjects were recruited. Serum TRAIL was measured by means of an enzyme-linked immunosorbent assay (ELISA). TRAIL and TRAIL receptors were evaluated by reverse transcription - polymerase chain reaction (RT-PCR) (RNA of lesional and non-lesional psoriatic skin) and by immunohistochemistry (lesional skin). Caspase 8 and NF-kB immunoexpression were also evaluated by immunohistochemistry.
Results: RT-PCR demonstrated increased synthesis of TRAIL and its receptors in lesional vs. non-lesional skin. Immunohistochemistry showed a strong staining of TRAIL and TRAIL receptors both in the epidermis and in the dermal infiltrate. Finally, a correlation emerged between caspase 8 and TRAIL immunoexpression in the dermis.
Conclusions: Our findings suggest an involvement of TRAIL in psoriasis pathogenesis, probably through an action at the site of the inflammatory infiltrate, likely via caspase 8.