Psoriasis is a chronic autoimmune disorder of the skin. In this disease, the inflammatory caspases, cysteine proteases involved in the processing of many proteins, are activated. Transgenic mice expressing the cleaved form of caspases by Lyn, a tyrosine kinase Src family, develop an inflammatory syndrome with the characteristics of human psoriasis.

To clarify the relationship between the cleaved form of Lyn by caspases and psoriasis, the investigators intend to develop a clinical study to analyze the expression, cleavage and activity of Lyn and the activation of caspases from skin biopsies of patients with this disease.

This study will be conducted on a cohort of patients with different forms of psoriasis (plaque, pustular and erythrodermic) and atopic dermatitis, another skin disorder associated with chronic inflammation. Thus, the investigators will evaluate the expression and activity of Lyn from skin lesion (L) and non-lesional (NL) from the same patient in parallel with the level of caspase activation and apoptotic inflammatory.

Thus, the investigators will verify that the cleavage by caspases of Lyn is associated specifically with psoriasis, as the investigators believe, or more generally to the skin inflammation. The investigators work would then define the cleavage by caspases of Lyn as a new potential marker of human psoriasis.

Inclusion Criteria:

Psoriasis arms:

• Plaque psoriasis and erythrodermic more than 10% of body surface area.

• Pustular psoriasis of at least 1% of body surface.

  • Atopic dermatitis arm:Patients with atopic dermatitis has been identified and inflammatory lesions on the skin.
  • Healthy arm:People not suffering from any skin disease

Exclusion Criteria:

• Systemic treatment of psoriasis for at least 4 weeks and / or local treatment for at least 2 weeks at the time of study entry.
• Patient with significant infection and / or immunocompromised.