Inclusion Criteria:

• - Man and Woman.

• - 18 to 50 years old.

• - Multiple Sclerosis diagnosed according to Mc Donald's criteria (Thompson et al.

2018)

• - With an acute relapse (group 1) - Stable with Natalizumab treatment (group 2), minimum 6 Natalizumab cures.

• - Healthy Volunteers (group 3)

  Exclusion Criteria:

  - without social security.

• - HIV positive serology.

• - infectious status in the past month.

• - corticosteroid therapy in the past month.

• - dementia.

• - pregnant or breastfeeding woman.

• - previous participation in the study.

• - under judicial protection.

- non-cooperating patient

The expression modulation of 5-HT7 receptor will be investigate in correlation with the immunological context, in different group of MS patients:

• - Group 1: MS patients with an acute relapse.

• - Group 2: MS stable patients treated with Natalizumab.

• - Group 3: Healthy people (from Etablissement Français du Sang) 1.

5-HT7 receptor expression evaluation on circulating leukocyte cells Each group presents a different inflammatory context. The investigator wish to determine the immunological context influence on the 5-HT7 receptor expression and which cells express it. To analyze the 5-HT7 expression on circulating leukocyte cells, The investigator will perform flow cytometry studies from the whole blood of the three groups mentioned above. In a first step, the investigator will analyze the overall rate of 5-HT7 circulating positive cells by the use of an antibody against 5-HT7 receptor whose specificity was validated in our research team. In a second step, the investigator will precise which cell type, among the lymphocytes implicated in the MS pathology, express the 5-HT7 receptor. The investigator will use antibodies against each population t helper cell: Th1 , Th2, Th17 and Treg. The investigator will also perform immunostaining on Cytospin (thin layer of blood cells on coverslips) to visualize co-labeling and confirm the results of flow cytometry. 2. Correlation between 5-HT7 receptor expression and mRNA quantity In addition, a correlation has been shown between an increase of 5-HT7 positive cells and an mRNA quantity up regulated. For the three groups, the investigator will determine the 5-HT7 mRNA quantity on circulating leukocyte cells. In a first step, the investigator will check correlation between the 5-HT7 receptor expression rate and the mRNA quantity on circulating leukocyte cells, using quantitative Polymerase Chain Reaction (qPCR). In a second step, the investigator will perform cell sorting to isolate Th1, Th2, Th17 and Treg cells and specifically extract 5-HT7 mRNA. In this way, the investigator can address the 5-HT7 receptor role on one or more specific cell types on the MS. 3. 5-HT7 receptor modulation according to the immunological context In order to understand the 5-HT7 receptor potential role on immune response moderation, the investigator will identify the immune context by ELISA dosage from serum samples. The investigator will investigate on pro-inflammatory markers like IL1b, IFNg, IL17 and anti-inflammatory markers like IL10 and IL4. These results will be correlated with the previous results concerning the 5-HT7 receptor expression/quantity for each patient groups. 4. 5-HT7 receptor role on lymphocyte functions in vitro From blood samples of the three groups mentioned above, the investigator will isolate peripheral blood mononuclear cells (PBMC) in vitro, to evaluate the 5-HT7 receptor role on their function to produce and release cytokines. The investigator will stimulate PBMC with one or more 5-HT7 ligands, and will perform ELISA dosage from supernatant with pro-inflammatory markers like IL1b, IFNg, IL17 and anti-inflammatory markers like IL10 and IL4. The cell immunolabelling will be perform to visualize 5-HT7 receptor on the cell surface. 5. Identification of 5-HT7 receptor isoforms There are three forms of 5-HT7 receptor (5-HT7a, 5-HT7b, 5-HT7d). However, no difference has yet been described for their pharmacological function. The investigator propose to identify these different isoforms by qPCR. As previously described, in a first step, on circulating leukocyte cells and in a second step, after cell sorting to isolate Th1, Th2, Th17 and Treg cells.

Arms

: Multiple Sclerosis patients with an acute relapse

Multiple Sclerosis diagnosed according to Mc Donald's criteria with an acute relapse

: Multiple sclerosis pataients treated with Natalizumab

Multiple Sclerosis patients diagnosed according to Mc Donald's criteria and treated with Natalizumab since 6 cures

: Healthy people

Interventions

Other: - blood sampling

Analyse of expression modulation of 5-HT7 receptor in correlation with the immunological context, in 3 differents groups : 2 with multiple sclerosis patients, one healthy volunteers group