S100A8 and psoriasis: In particular, it has been shown that p38 MAPK activity is increased in lesional compared to non-lesional psoriatic skin [13]; moreover, the antimicrobial peptide S100A8, known to be upregulated in lesional psoriatic skin and believed to play a role in the pathogenesis of psoriasis, was found to be regulated by a p38 MAPK-dependent mechanism in cultured human keratinocytes [60].