The Microbiome in Psoriasis and Psoriatic Arthritis: The Skin Perspective

Psoriasis is a chronic, inflammatory immune-mediated skin disease that affects about 2% of the world's population. In 20% of patients with psoriasis, the characteristic skin lesions are accompanied by psoriatic arthritis (PsA). Psoriasis arises in genetically predisposed individuals who have a dysregulated immune response to various environmental factors. The human body is home to many microbial species, and both the skin and the gut microbiome influence the development and function of immune tissue development and function. Studies on the cutaneous microbiome show a trend toward an increased relative abundance of Streptococcus and a decreased level of Propionibacterium in patients with psoriasis compared to healthy controls. In the gut microbiome, the ratio of Firmicutes and Bacteroidetes was perturbed in psoriatic individuals compared to healthy controls. Actinobacteria was relatively underrepresented in patients with psoriasis compared to healthy individuals. A decrease in skin microbiome flora diversity seems to be a sign that a patient with psoriasis is at elevated risk for developing arthritis. Modulating the skin microbiota for therapeutic reasons can be achieved by antimicrobial (antibiotic) therapy, the application of prebiotics or probiotics, or the transplantation of an entire healthy microbial population.