Background: Quantification of the IgG subclasses (IgGS) requires highly sensitive and specific techniques since their molecular structure is more than 95% homologous. At present, ELISA and RIA are the most appropriate techniques; although the variability of these techniques and the possible ethnic differences in serum levels of IgGS oblige each laboratory to establish its own reference values in a normal population, a condition necessary for defining IgGS deficits.
Methods: In the present study the normal serum values of IgGS in 100 healthy individuals were established. Serum quantification of the IgGS was performed by optimization of the indirect ELISA technique using AcMo and OMS reference standards H00-03 for the 4 subclasses, calibrated vs the OMS WHO 67/97 pattern.
Results: Normal values observed for IgG1 were 2.61-10.81 g/l; IgG2, 1.12-4.08 g/l; IgG3, 0.22-2.88 g/l; and IgG4, 0.05-1.56 g/l obtained as of the mean +/- 2 SD for IgG1 and as of the extent of the values of the remaining 3 subclasses by following a non-normal distribution. The sensitivity of the technique was 0.05 g/l with mean intra and inter analysis coefficients of 3.5% and 10.7% respectively. The correlation between total IgG and the sum of the 4 subclasses showed a r = 0.894 (p less than 0.01).
Conclusions: The ELISA technique using AcMo and OMS reference standards is an adequate method for the quantification of the IgG subclasses. However, given the variability of this technique and in order to avoid error, strict working conditions, such as the use of control sera at 2 concentration levels, should be observed for the 4 IgGS in each of the analytic series and each series should also be duplicated.