The project topic consists on re-conciliating the fine tuners of the gene expression "microRNAs" and the immunopathogenic occasions responsible for skin disorders in context of skin infection and inflammation such as psoriasis. The skin is a network of effector cells and molecular mediators that constitute a highly sophisticated "Skin Immune System (SIS) described by Jan D Bos in 1986. The cutaneous homeostasis maintenance is dependent on the cross talk between several immune sentinels present in the different compartments of the skin as well as the interplay between innate and adaptive immune responses. The whole is under the control of gene regulation. However, cutaneous homeostasis disruption occurs when the SIS safe framework erroneously sends aggravation signals due to gene regulation disbalance via inflammatory cellular and molecular mediators into the site of infection causing chronic inflammation characterized by thick red irritated skin lesions. The latter was showed to have a characteristic microRNA (regulators of gene expression) signature.

Inclusion Criteria:

• Men or women between 18 and 75
• Clinical diagnosis of chronic active psoriasis in non-pustular plaque
• Treated locally with topical corticosteroids

Exclusion Criteria:

• Patient who did not give express consent to participate
• No affiliation to a social security scheme
• Patient treated systemically
• Thrombocytopenic patient
• Patient known to be HIV-positive
• Septic patient
• Patient with only facial lesions
• Patient with psoriasis with joint involvement
• Patient participating in another study
• Patient protected under the law (under guardianship or trusteeship)
• Pregnant or lactating woman