CD79A and Recurrent upper respiratory tract infections: It is also capable of neutralizing toxins and viruses.1,2 A study of humans with mucosal humoral immunodeficiencies suggests that the absence of s-IgA leads to an increase in mucosal infections and respiratory tract infections.3 Moreover, suppression of s-IgA is associated with increased incidence of upper respiratory tract infection (URTI) in elite athletes4,5 and healthy adults.6