[Serum levels of IgG subclasses in the normal child. Evaluation by an immunoenzymatic method using monoclonal antibodies].

Serum IgG subclass levels were measured by an immunoenzymatic assay with monoclonal antibodies in 225 normal children aged 1 to 17 years. Adult concentrations of IgG1 and IgG3 were reached early (2 to 3 years of age), with mean IgG1 level slightly higher in children than in adults, whereas IgG2 and IgG4 showed a slow increase. Mean IgG2 levels in children aged 13 to 17 were still significantly lower than in adults. The distribution of IgG4 levels in every age group was very heterogeneous, with a fair incidence of subthreshold concentrations especially before 5 years of age. These data must be taken into account when defining IgG subclass deficiencies in children.