Light microscopic image of the lesion showing hyperkeratosis on the surface, thickening of the granular layer, and marked
psoriasiform hyperplasia (hematoxylin-eosin staining, x40).
A skin biopsy showed only mild
psoriasiform hyperplasia, occasional dermal eosinophils, and no neutrophils.
Histopathology of the lesion revealed
psoriasiform hyperplasia, hyperkeratosis, parakeratosis, spongiosis and few necrotic keratinocytes in upper epidermis.
The histopathological findings are parakeratosis and
psoriasiform hyperplasia with neutrophilic infiltration into the epithelium.
IL-22 is another key downstream cytokine in the IL-23/Th17 axis, being upregulated in psoriatic skin as compared to normal skin [5, 29, 40, 41]; IL22 mediates keratinocyte hyperplasia via STAT3 activation, leading to
psoriasiform hyperplasia. In the absence of IL22, severity of both IL-23-mediated and imiquimod-induced psoriasis-like dermatitis in corresponding mouse models is markedly reduced [40,42, 43].