CD40LG and inborn error of immunity: Individuals with low levels of serum IgA, IgG, and/or IgM (hypogammaglobulinemia) are prone to infections and various other complications, including autoimmune disorders and malignancies, as can be seen in patients with common variable immunodeficiency, a primary immunodeficiency (PID) characterized by low levels of IgG with low IgA and/or low IgM levels [2–6].