The pathogenic role of type I interferons (IFNs) in the development of different autoimmune diseases has been extensively described in the literature. Since plasmacytoid dendritic cells (pDCs) are the main source of type I IFNs, there is evidence of the involvement of pDCs in autoimmune diseases. The CD303 surface protein (also called BDCA-2) is specifically expressed by the pDCs.

The hypothesis leading to the realization of this study is to observe, in vitro, an inhibition of the secretion of the type I IFNs by pDCs in the peripheral blood in patients with autoimmune disease, thanks to the action of the anti-CD303 antibody Developed by the LFB Group, which could reduce the inflammatory response and improve patients with autoimmune disease

Inclusion Criteria:

• Have the ability to understand the requirements of the study, provide written informed consent, and comply with the study data collection procedures
• Patient followed in the department of internal medicine of CHU Lille
• Patient with one of the following autoimmune disease, defined according to international criteria: systemic lupus erythematosus, systemic sclerosis, Gougerot-Sjögren syndrome and idiopathic thrombocytopenic purpura
• Being socially insured

Exclusion Criteria:

• Overlapping syndrome with another autoimmune disease
• Age ≤18 years
• Pregnant or nursing women
• People in emergencies
• Person incapable of consent
• Persons deprived of liberty
• Persons without social security cover