The serum IgG subclass levels in healthy infants of 13--62 weeks of age.

The levels of IgG1, IgG2, IgG3, and IgG4 were determined in serum samples of 160 infants aged 13--62 weeks, and of their mothers. In addition the serum IgM, IgG, IgA, and IgD levels of the infants are presented. The results show that IgM, IgG1, and IgG3 slightly increase during the first year of life, whereas IgG2, IgG4, IgA, and IgD hardly do. This difference in the development of the various immunoglobulin isotypes reflects differences in the terminal maturation of subsets of B-lymphocytes into plasma cells. About 50% of the infants of this age had no detectable IgG4 and three children had no IgG2. These observations indicate that longitudinal investigations are needed in children suspected of a IgG2 or IgG4 subclass deficiency. No statistically significant influence of sex on the IgG subclasses could be demonstrated in these infants.