*3.1. IMQ-Based Experimental Murine Model of Psoriatic Dermatitis*

The experimental model of psoriatic dermatitis was performed to evaluate the effect of the IgY treatment on Ps-specific skin and systemic lesions. The murine model of psoriatic dermatitis previously described [43,44,47], used IMQ-based cream applied on the back skin area for 6 consecutive days in order to induce an extensive psoriatic-like reaction. Animals were monitored daily, and the severity of skin inflammation induced by applying IMQ-based cream was assessed based on daily scores of erythema, thickening and skin scaling, PASI score, splenomegaly evaluation and histopathological assessment. Erythema, thickening and scaling of the back skin were daily scored on a 0–4 scale (0—no change, 1—mild change, 2—marked change; 3—significant change, 4—severe change) and the evolution of these scores is shown in Figure 1a. Table S1 presents the individual PASI scores for all the animals within the groups. ɛ −

Starting with day 2, signs of inflammation were visible and increased in intensity until the end of the application. The skin on the back region of the mice began to show signs of erythema, thickening, and scaling that became visible from day 3 of the experiment. As a measure of the disease severity, a modified PASI score (0–12 scale) was calculated daily, by summing erythema, thickening and skin scaling daily scores. The PASI cumulative score had a progressive evolution, reaching high values at the end of the applications (Figure 1b).

**Figure 1.** *Cont*.

**Figure 1.** Evolution of in vivo parameters and histopathological assessment of dorsal skin samples. (**a**) In vivo measurements scores for erythema (0 ± 0; 1.1 ± 0.2; 2.1 ± 0.4; 2.6 ± 0.4; 3.3 ± 0.4; 3.4 ± 0.4; 2.8 ± 0.4), thickening (0 ± 0; 0.4 ± 0.6; 1.2 ± 0.4; 2 ± 0.4; 2.8 ± 0.4; 3.3 ± 0.4; 3.7 ± 0.4) and skin scaling (0 ± 0; 0 ± 0; 1.1 ± 0.3; 1.6 ± 0.4; 2.6 ± 0.4; 3.2 ± 0.5; 3.5 ± 0.3) scores; (**b**) PASI scores (0 ± 0; 1.5 ± 0.6; 4.4 ± 0.6; 6.2 ± 0.8; 8.7 ± 0.6; 8.7 ± 0.6; 9.9 ± 0.7). The results are presented as mean score ± SD; *n* = 28 (*n* = number of mice; D = day); (**c**) H&E staining of the back skin samples provided from normal mouse (control group); (**d**) H&E staining of the back skin samples provided from IMQ-induced mouse (Ps group). IMQ-based cream induces hyperkeratosis, parakeratosis, acanthosis and elongation of rete ridges.

Skin inflammation induced by IMQ-based cream was histopathologically assessed. Skin samples harvested from all groups were collected at the end of experiment, fixed in 10% buffered formaldehyde and incorporated into paraffin; the paraffin blocks were sectioned (5 µm thick sections), stained with hematoxylin-eosin and examined by pathologist. Histopathological evaluation revealed hyperkeratosis, parakeratosis, acanthosis and elongation of the red ridges, histopathological features typical for human psoriatic lesions (Figure 1d). None of these features were observed in healthy mice (control group) (Figure 1c). Individual data for the assessment of all histological parameters and individual mice are presented in Table S2 (Supplementary Material).
