BCR and common variable immunodeficiency: In parallel, lower levels of CD5 (found in common in the three CVID groups 1 to 3) together with a marked reduction of the amount of CD19 expressed/B-cell, particularly in CVID group 2 cases, may further affect the activation threshold (53) required for BCR-mediated B-cell activation and subsequent maturation of immature and naive B-lymphocytes to MBC and plasma cells in this group of CVID patients.