IL17A and psoriasis: Currently, four classes of biologics are available for psoriasis treatment: inhibitors of TNF-α (adalimumab, etanercept, infliximab and certolizumab pegol), IL-17 (secukinumab, brodalumab and ixekizumab), IL-23 (tildrakizumab, risankizumab and guselkumab) and IL-12/23 (ustekinumab) [11].