The effect of therapy on TRM in psoriatic lesions

Introduction
The course of psoriasis is associated with recurrence of the lesions at the same location despite effective treatment. It is due to the presence of TRM (tissue-resident memory cells) in the seemingly healthy skin, which may initiate an inflammatory cascade.

Aim
The assessment of TRM in psoriatic lesions prior to and after 12 weeks of systemic therapy with methotrexate (MTX) or secukinumab (SEC) or ixekizumab (IXE) or adalimumab (ADA).

Material and methods
TRM markers (CD4, CD8, CD103, CD69, CD49, CXCR6) and the tissue expression of cytokines (IL-17, IL-22) in the psoriatic lesions obtained from 13 patients compared to 10 healthy skin samples were evaluated with immunohistochemistry. Biopsy specimens were collected three times from the same psoriatic plaque before and after 4 and 12 weeks of therapy.

Results
The expression of TRM markers in the lesions decreased at three time points (W0, W4, W12), revealing the diminished intensity of fluorescence over time with each therapy. The most rapid response was observed with anti-IL-17 therapy at W4 of treatment, while with MTX and ADA at W12.

Conclusions
The decreased expression of TRM markers occurring predominantly in the lesional dermis and not in the epidermis over 12 weeks of observation may be due to the poorer penetration of systemic drugs to the epidermis, or the process of psoriatic lesion regression in the epidermis is secondary to the reduction of inflammation in the skin, or TRM in the epidermis may be more resistant to therapy.