Elevated levels of IgM antibodies have been found in the serum of patients with visceral leishmaniasis who are in the acute phase of the disease, IgM levels remain high in patients resistant to sodium stibogluconate (SAG), and patients who respond to SAG showed a decrease in the levels of total IgG, IgM, and IgE [53]. The gene discussed is CD40LG; the disease is visceral leishmaniasis.