MBL2 and respiratory tract infectious disorder: A recent clinical study by Kainulainen et al. [94] provided preliminary data which are consistent with our hypothesis that synergy between C4 deficiency and MBL excess may predispose children and adolescents to certain infections: 26% (n = 22) of Finnish patients with recurrent respiratory infections vs.14% (n = 10) of healthy controls (p = 0.048) had C4A deficiency.