IL17A and psoriasis: Obesity is a pro-inflammatory state, where the adipose tissue is invaded by activated M1-type macrophages and B- and T-lymphocytes, with an over-production of cytokines, such as tumor necrosis factor-α (TNFα) and interleukin (IL)1, IL6, IL17 and IL23, which are all involved in the pathogenesis of psoriasis and PsA [49, 50].