For example, reduced numbers of memory B cells are included in the classification of Common Variable Immunodeficiency (CVID), which is characterized by recurrent infections, decreased IgA or IgM and hypogammaglobulinemia (6), as not all those with reduced IgG suffer from CVID and not all patients with CVID have low IgG. This evidence concerns the gene CD40LG and common variable immunodeficiency.