Secretory IgM-deficient (sIgM−/−) mice have increased susceptibility to respiratory infection with C. neoformans compared to control mice and exhibit defects in Th1 polarization and phagocytosis of fungi by alveolar macrophages; the defect in phagocytosis can be ameliorated by administration of IgM into the lungs [100]. This evidence concerns the gene CD40LG and respiratory tract infectious disorder.