## 2 Materials and Methods  
Non-invasive live imaging was conducted with the deepLiveTM LC-OCT device (DAMAE Medical, Paris, France), which uses an 800 nm wavelength laser. It can generate vertical (1.2 mm \(\times\) 0.4 mm) and horizontal pictures (1.2 mm \(\times\) 0.5 mm) as well as 3D stacks (1.2 \(\times\) 0.5 \(\times\) 0.5 mm\({}^{3}\)), simultaneously capturing dermoscopic pictures. The application of immersion oil (paraffin oil) is necessary [23; 24; 25]. Because of the high resolution, it generatesvisuals similar to histologic slides. A live video sequence can be captured, which enables the visualization of blood flow. A second probe, containing a videodermoscope, is connected to the device and can be used separately. It allows for the colocalization of the LC-OCT pictures within the previously taken dermoscopic images. For this prospective observational study, 12 patients with clinically or histologically confirmed PP, newly receiving treatment with an IL-17 inhibitor, were examined [26]. We focused on one group of therapeutic agents in order to minimize therapeutic outcome variations between different biologic subgroups and because IL-17 inhibitors have emerged as a highly effective class of biologics for treating moderate-to-severe plaque psoriasis. These drugs have demonstrated superior efficacy compared to many other treatment options, with some studies showing they can achieve \"clear skin\" for a significant proportion of patients [26]. The robust clinical response and rapid onset of action observed with anti-IL-17 drugs thus presumably also suggested a rapid improvement in psoriasis changes in LC-OCT, which is why this subgroup of drugs was selected for this study. Aforehand, approval from the ethics committee was obtained. Treatment decisions, screening before the therapy, and monitoring during therapy were carried out at our outpatient clinic, and were not influenced by participation in the study. Patients were included after obtaining their written, informed consent. They were eligible if the study lesion was not treated with topical corticosteroids 2 weeks prior to study initiation and if the biologic treatment was newly administered. Exclusion criteria were the regular use of topical corticosteroids in the last 2 weeks prior to inclusion on the chosen psoriatic plaque, the continuation of another, already prescribed systemic treatment, and a lesional psoriasis severity index (LPSI) lower than 5 in all psoriasis plaques. A study plaque (SP) and control area (CoA) were chosen before the initiation of therapy. The SP's localization was not restricted; the CoA had to be clinically healthy skin and, if possible, located in a body region similar to that of the SP. Therapeutic response in the SP was evaluated by changes as observed by LC-OCT and, clinically, by determining the LPSI. The LPSI was designed in accordance with the LPSI already established by [PERSON] [27] as a five-point scale (scaling (0-4), erythema (0-4), and infiltration (0-4)), ranging from 0 to the highest score of 12. The overall therapeutic response was assessed using the PASI score and DLQI. The probability of psoriatic arthritis was screened for with the German psoriasis arthritis diagnostic questionnaire (GEPARD). Patients underwent the first screening before starting the new treatment (V0), as well as 4 weeks (V1) and 12 weeks (V2) after the initiation of therapy. Use of topical corticosteroids on the SP was omitted during this period in accordance with the patients. The LC-OCT scanning of the SP and CoA, dermoscopy, clinical photography, and the assessment of the LPSI, PASI, DLQI, and GEPARD were conducted at all study visits by our investigator team. For one patient, the DLQI and GEPARD were missing for V2. LC-OCT scanning was performed by capturing a 3D stack at three different areas in the SP and CoA after the application of paraffin oil. The best scan of each lesion and time point was chosen for analysis, including a manual measurement of hyperkeratosis/stratum corneum (SC) and ET (see Figure 1a-c).