Distribution of IgG subclass levels in normal adult sera as determined by a competitive enzyme immunoassay using monoclonal antibodies.

IgG subclass levels were measured by an indirect competitive immunoenzymatic assay with selected monoclonal antibodies in sera from 180 adult blood donors. Mean levels were 6.35 mg/ml (65% of the sum of the subclasses) for IgG1, 2.61 mg/ml (26.2%) for IgG2, and 0.414 mg/ml (4.3%) for IgG3. IgG4 levels were significantly different in men (mean 0.456 mg/ml, 4.8% of the sum) and women (mean 0.29 mg/ml, 3.2%), with very wide ranges. The distribution of IgG2 levels was more homogeneous than that of IgG4 but more heterogeneous than those of IgG1 and IgG3, with a number of sera that displayed low levels of IgG2.