Serum immunogiobulin G subclasses and serum immunogiobulin A in healthy Norwegian children and adults

Abstract

IgG subclass concentrations were determined by a capture ELISA antibody assay using monoclonal antibodies to IgG1, IgG2, IgG3, and IgG4. All the antibodies had been tested for specificity in an IUIS/WHO collaborative study, and this was confirmed by us by testing against purified myeloma proteins representing the 4 subclasses. The sera to be tested were diluted to obtain optimal sensitivity in the lower normal range for each subclass. With these serum dilutions, the lower limit of reading was 1. 2 g/l for IgG1, 0. 25 g/l for IgG2, 0.04 g/l for IgG3 and for IgG4. Age specific reference limits of the IgG subclass concentrations were determined in serum samples from 138 healthy infants and children under 14 years of age and 66 adults. The reference limits for each age group were determined by calculating the mean ± 2 SD of the logarithms to the values and then taking the antilog of the results. IgA was determined by a turbidimetric method with a reading limit of 0. 1 g/l, and the reference limits were calculated from serum samples from the 138 children under 14 years of age and from 31 healthy adults. The age specific reference limits of the IgG subclasses and IgA are given. Several infants and children had IgG4 levels below the lower reading limit. To determine lower reference limits of IgG4 below the age of 7 years was therefore of little clinical significance.