While ≥90% of the healthy individuals presented with easily detectable (≥100 RU) anti-A/B IgM and IgG antibodies, anti-A/B IgG antibodies were undetectable or very low (<100 RU) in all 20 CVID patients investigated (Figure 4, upper panel), Six of these 20 patients also had very low to undetectable anti-A/B IgM-antibodies (CVID_M_low in Figure 4, lower panel), while levels of anti-A/B IgM-antibodies in the remaining patients (CVID_M_normal in Figure 4, lower panel) were comparable to the healthy control group. Here, CD40LG is linked to common variable immunodeficiency.