[Anti-IL17 induced eczema and the yin-yang of Th2 and Th17].

Biologics targeting specific cytokines and pathways have revolutionized the management of patients with chronic inflammatory diseases. However, these treatments have their limitations and, surprisingly, can induce novel inflammatory diseases. Here, we present a case of a psoriasis patient developing anti-IL17 induced eczema, an intriguing side effect of IL-17 blockade. The coexistence of psoriasis and eczema in a single patient is uncommon given their distinct and opposing immune mechanisms. Psoriasis is mainly driven by Th17 cells, whereas atopic dermatitis is Th2-dominated. In this article, we propose the yin yang of Th2 and Th17 with IL-4 and IL17 as principal antipodal vectors that control each other. Thus, blocking one of these cytokines can tip the balance between Th2 and Th17 and lead to the induction of the opposing inflammatory pathway via lifting the controlling mediator.