Interleukin-8 is induced in skin equivalents and is highest in those derived from psoriatic fibroblasts.

Interleukin-8 (IL-8) may be important in psoriasis as it is expressed in the stratum granulosum, attracts polymorphonuclear cells, and stimulates angiogenesis and keratinocyte mitogenesis. To study intrinsic cutaneous factors in psoriasis, we constructed skin equivalents from psoriatic or adult control fibroblasts with normal foreskin keratinocytes. IL-8 levels were measured in supernatants by enzyme-linked immunosorbent assay and in skin equivalents by immunohistochemistry and in situ hybridization. IL-8 was highly induced in skin equivalents compared to cells grown alone. Epidermal stratification varied among fibroblast lines and was correlated with IL-8 levels, but lesional and nonlesional psoriatic skin equivalents from the same donor were similar. Six fibroblast lines (two psoriasis lesion and four normal) supported only monolayers, while 12 lines (seven psoriasis lesion and five normal) produced stratification. Mean IL-8 levels were significantly lower in dermal equivalents of the first group than the second (0.78 +/- 0.40 vs 3.93 +/- 2.83 ng per ml, mean +/- SD, p = 0.01, analysis of variance). Significantly more IL-8 was secreted by psoriatic than normal fibroblast skin equivalents over 14 d (p = 0.015) with greatest differences at 1 and 4 d. Psoriatic IL-8 levels peaked first and remained increased. IL-8 protein and mRNA were initially strongest in dermal fibroblasts, and at the dermal-epidermal interface. Diffuse epidermal expression was replaced by accentuation in the stratum granulosum. Psoriatic skin equivalents were thicker, had more intense IL-8 staining, and developed invagination. We hypothesize that an IL-8 paracrine loop between fibroblasts and keratinocytes may play a key role in epidermal regeneration in the skin equivalent, in normal wound healing, and in the determination of an intrinsic psoriatic wound-healing phenotype.