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Our aim is to determine whether whether Tph could support non-infectious complications through providing help to pathological B-cells.

Common variable immunodeficiency (CVID), the most common symptomatic primary immunodeficiency in adults, can associate recurrent infections with severe non-infectious complications. Unfortunately, there is still no absolute biomarker predicting which CVID patient will develop non-infectious complications. Thus, novel biomarkers which could help refining CVID patient prognosis require further investigations. Moreover, the immune mechanisms driving non-infectious complications remain elusive. Therefore, further insight into CVID pathophysiology is needed to discover new treatments for CVID patients with non-infectious complications (CVIDc). Our preliminary results show that CVIDc patients have an increase of circulating peripheral helper T-cells (Tph) , in comparison with patients with infectious manifestations only (CVIDi) and healthy individuals (HI). Recently described, Tph express CXCR3, help memory B-cells and are found in inflamed tissues in auto-immune diseases. They represent a major reservoir of auto-reactive T-cells, suggesting that Tph are key to drive auto-immune processes. Some authors hypothesized that Tph can help atypical memory B-cells (ABCs), a B-cell subset which is involved in auto-immune disease pathophysiology and which is also expanded in CVIDc patients. The ivestigators observed that CXCR3+ cells were increased in the spleen of CVIDc patients in comparison with non-CVID controls. These CXCR3+ cells could correspond to Tph supporting extra-follicular reaction and then B-cell tolerance loss. Our hypothesis is that alterations in T-B cell collaboration leads to the amplification of Tph in CVID patients. Tph could support non-infectious complications in target tissues through providing help to pathological B-cells such as ABCs. Using peripheral blood from CVIDc/CVIDi patients and HI, the investigators will determine whether Tph support pathological B cell activation in CVIDc patients using T-B co-cultures. Patients will be included during their routine follow-up, for one day.