1114 Study of long-term (15-day) imiquimod treatment and drug intervention in localized psoriasiform dermatitis model

Imiquimod (IMQ)-induced acute skin inflammation is the most widely used animal model in the field of psoriasis research. Several information is already available on the effect of IMQ in acute dermatitis, but little is known about its long-term application. Here, in this study we tested the long-term IMQ treatment and the effect of an anti-inflammatory drug in two mouse strains in different experimental setups using the localized psoriasiform dermatitis model. Aldara cream (5% IMQ) was applied in Finn chamber on the dorsal skin of C57BL/6J or Balb/c mice during the first 4 days of the 15-day experiment and every second or third day afterwards in separate groups. Vaseline or corticosteroid ointment were applied on the intermediary days. Skin thickness, blood perfusion, body weight and local PASI were calculated daily. Skin samples were collected on days 5, 10 and 15 of the experiment. Histopathological alterations were evaluated on H&E stained sections, while inflammatory cytokines were determined by qPCR and Luminex technology. Clinical signs of skin inflammation were most intensified on Day 5 of the experiment in each treatment groups of Balb/c or C57BL/6J mice, then the skin regained its normal phenotypical appearance. From Day 12 of the experiment, hair growth was observed in the Aldara-treated dorsal skin areas in each group of both animal strains, except in steroid treatment group. Skin infiltration increased in both animal strains until 5th day of the experiment and then a second peak developed from 10th day until the end of the experiment. Topical corticosteroid significantly reduced skin infiltration from day 6 in both animal strains. Inflammatory cytokines were significantly reduced after topical corticosteroid treatment on days 10 and 15 of the experiment. Our results proved that the application of Aldara in Finn chambers enables the study of the effect of long-term IMQ treatment. Furthermore, our experimental setup may be used to investigate topically applied anti-inflammatory drug candidates in psoriasiform dermatitis.