Fig. 1. Immunohistochemical stain of skin section with monoclonal antibodies against IL-19 and IL-20. Healthy skin (A): strong expression of IL-20 in some perivascular mononuclear cells (could be dendritic cells); weak positive (+/−) in epidermal basal cells; and hair follicles. IL-19 was expressed in the basal portion of the epidermis (about 3 layers) and hair follicles varying from 2+ to 3+. Psoriasis (B): diffuse cytoplasmic staining of IL-20 on basal and suprabasal keratinocytes of epidermal keratinocytes, varying from weak to 1–2+, compared with the weak staining on basal keratinocytes in healthy skin samples. IL-19 was localized in the lower half of the epidermis: 2+ to 3+ in intensity. Spongiotic dermatitis (eczema) (C): diffuse cytoplasmic staining of IL-20 in the epidermis, varying from 1+ to 2+. IL-19 was concentrated in the lower half of the epidermis, varying from 2+ to 3+, with stronger staining in inflamed eczematic foci. Staining with mouse IgG1 isotype was used as the negative control.

Fig. 2. Immunohistochemical stain of skin section with antibodies against IL-20R1 and IL-20R2. Healthy skin (A): IL-20R1 and IL-20R2 were weakly stained on basal and suprabasal keratinocytes in healthy skin samples. Psoriasis (B): staining of IL-20R1 and IL-20R2 on an entire layer of epidermal keratinocytes. Spongiotic dermatitis (eczema) (C): diffuse staining of IL-20R1 on basal and suprabasal keratinocytes of epidermal keratinocytes. IL-20R2 was localized in the lower half of the epidermis: 2+ to 3+ in intensity. Staining with mouse IgG₁ isotype was used as the negative control for IL-20R1. Staining with rabbit pre-immune IgG alone was used as the negative control for IL-20R2.

Fig. 3. Upregulation of IL-20, IL-20R1, and IL-20R2 transcripts in psoriatic epidermis. (A) IL-20 transcript was amplified on epidermis of all three types of skin samples. Amplified PCR fragments of IL-20 and HPRT from the epidermis of three types of skin samples were loaded on agarose gel. The expression level of IL-20 is illustrated by a bar representing relative expression to HPRT. N/D, no detectable transcript. (B) The expression of IL-20R1 and IL-20R2 transcripts on epidermis from psoriatic lesion and healthy skin was detected with RT-PCR. The expression amount of IL-20R1 and IL-20R2 was divided by that of HPRT. The relative expression of IL-20R1 (open bar) and IL-20R2 (closed bar) is illustrated by a bar. The data represent three healthy controls and three psoriasis patients.

Fig. 4. Specificity of monoclonal antibody against IL-20. Cytokines of IL-10 family–IL-19 (Lane 1), IL-22 (Lane 2), IL-24 (Lane 3), IL-26 (Lane 4), and IL-20 (Lane 5)–were loaded on SDS-PAGE and detected using Coomassie blue staining (left) and Western blot with anti-IL-20 monoclonal antibody in 1:1000 dilution (right).

Fig. 5. IL-20 level in the blood of psoriasis patients (●; n = 42) and healthy controls (○; n = 42) was determined using ELISA. Horizontal bars show mean values of IL-20 concentration in serum of healthy controls (215 ng/ml) and psoriasis patients (67.2 ng/ml) (P = 0.0004 (two sided); Student's t test).

Fig. 6. IL-20 induced KGF transcripts in CD8-positive T cells. Values indicated on the top of each bar are expressed as 2^−ΔΔCt, corrected using β-actin expression, and relative to untreated cell levels. CD8+ T cells were cultured with or without IL-20 (100 ng/ml) for 1 h. Total RNA was extracted, and RT/real-time PCR amplification was performed with oligonucleotides specific for KGF.