An additional potential type of biomarker is the cutaneous expression of anti-microbial peptides (AMPs). Initially identified in frog skin, AMP expression in human psoriatic skin, specifically human beta defensin 2, was identified almost two decades ago. Since then it has become clear that a range of AMPs are highly expressed in the involved skin of psoriatic patients compared to normal skin. These proteins serve a protective antimicrobial function in the skin, but at the same time they may also play an immunomodulatory role. Therefore, it is conceivable that they may influence the pathophysiology of psoriasis. Indeed, the AMP cathelicidin (LL37) was shown to modulate proinflammatory keratinocyte responses in vitro, leading the authors to speculate that LL37 "may promote IL17/IL22 and IL6 associated psoriasis.". Thus, it is at least possible that treatment with IL17-targetting biologics not only influences the cutaneous expression of AMPs, but also alters the cutaneous inflammatory milieu, which may in result in profound changes in the cutaneous bacterial flora which the skin supports.