We used three different techniques, the DiaMed-ID Micro Typing System, a blood group ABO flow cytometry based assay (15), and the surface plasmon resonance technology (SPR) using the Biacore® device and synthetic AB trisaccharides (16–18) to study the blood group anti-A/B IgG and IgM antibody titer in an isotype-specific assay and the on/off rates of the binding of the respective antibodies to defined blood group A/B trisaccharides in CVID patients and healthy individuals. This evidence concerns the gene CD40LG and common variable immunodeficiency.