IL17A and psoriasis: Interleukin-17 (IL-17)-producing helper T-cells (Th17-cells), a subgroup of CD4+ cells, which are part of the adaptive immune system, play a central role in protection against infections and in autoimmune diseases such as human psoriasis, multiple sclerosis (MS), inflammatory bowel disease (IBD), Crohn’s disease, asthma, rheumatic arthritis and ulcerative colitis [18–22].