Detection of psoriasin/S100A7 in the sera of patients with psoriasis

Background  Psoriasis is a disease of dysregulated inflammation and epithelial hyperproliferation in the skin, involving both the innate and adaptive immune system. Psoriatic keratinocytes express high levels of psoriasin (S100A7), a small calcium-binding protein.
Objectives  To determine if patients with active psoriasis have elevated serum levels of psoriasin and psoriasin-specific autoantibodies.
Methods  Blood was collected from 14 patients with psoriasis vulgaris at the start of narrowband ultraviolet (UV) B therapy and from 11 of these patients every 2 weeks during the course of the UVB treatment. Patient and control sera were tested for psoriasin antigen levels by sandwich enzyme-linked immunosorbent assay, and for psoriasin autoantibody titres using recombinant purified psoriasin and overlapping peptides.
Results  We confirmed strong and specific expression of psoriasin in psoriatic epidermis by immunohistochemistry. Systemic psoriasin antigen levels tended to be lower in patients (mean 213 ng mL⁻¹) than in controls (mean 331 ng mL⁻¹, P  =   0·308) and decreased with increasing disease severity. Psoriasin-specific autoantibodies were detected in a subset of patients with psoriasis and healthy normal donors (mean 0·347 vs. 0·255 units, P  =   0·246). The epitopes recognized by the autoantibodies were mapped to an external loop domain of the molecule but did not show corresponding T-cell immunogenicity.
Conclusions  Although psoriasin is overexpressed in psoriatic skin lesions, systemic levels of psoriasin tended to be lower with increasing disease severity, which may be due to the presence of psoriasin-specific autoantibodies. Neither psoriasin nor psoriasin-specific autoantibodies appear to be promising serum biomarkers for clinical psoriasis.