Isotype, subclass and molecular size of immunoglobulins in salivas from young infants

Whole saliva samples from 17 infants who were between 3 and 20 weeks of age were analysed for isotype, subclass and molecular size of immunoglobulins. IgA concentrations ranged from 1.7 to over 60 micrograms/ml. IgM concentrations ranged from undetected to 59% of the IgA concentration in the respective saliva. Ratios of salivary IgM to salivary IgA were inversely correlated with the age of the infant. Gel filtration of 31 salivas on calibrated columns of Superose 6 revealed the IgA to elute in a position consistent with that of secretory IgA. IgM eluted in a position consistent with that of the pentameric molecule. IgA1 was the predominating subclass (IgA1/IgA1 + IgA2 = 0.64) in infant whole saliva. Both IgA subclass concentrations were significantly lower than concentrations measured in adult parotid salivas. Several infant salivas initially contained greater than 95% IgA1 but salivary IgA2 concentrations progressively increased as these infants grew older. These observations support the conclusions that essentially all IgA in whole saliva of predentate infants is of secretory origin, that adult salivary IgM/IgA proportions are achieved early in life, but that, at least in some infants, the salivary IgA subclass proportions are still changing during this time.