In our studies, as well as in the study by Hahn-Zoric et al.,147 it was shown that in nursing mothers with Common Variable Immunodeficiency (CVID) in IVIG therapy or with selective IgA deficiency, increased IgG and IgM antibody levels in milk constitute a compensatory mechanism for the lack of SIgA in the mucosa, and the biological action of these antibodies was as efficient as that observed in healthy women.147, 148, 149. The gene discussed is CD40LG; the disease is common variable immunodeficiency.