These IEIs all share hypogammaglobulinemia, reduced IgM+ and class-switched memory B cells, few or poorly formed GCs, and diminished specific Ab responses (de la Morena, 2016; Ma et al., 2007; Renner et al., 2021; Salzer et al., 2014; Schepp et al., 2017; Warnatz et al., 2006). This evidence concerns the gene CD40LG and agammaglobulinemia.