Quantitative and qualitative analysis of human IgG subclass specific mRNA using solution hybridization.

Four IgG subclasses have been identified in the human system. Despite the fact that they exhibit differences in their functional properties, antigenic properties and chemical composition and demonstrate age-related shifts in their expression, the genes coding for their constant regions show extensive homology at the nucleotide level (greater than 95%). The only parts of the C gamma genes that show significant variation among the different IgG subclasses are the exons coding for their hinge regions (less than 60%). Taking advantage of such sequence variation, we have developed specific RNA probes which allowed us to analyse the expression of the C gamma 1, C gamma 2, C gamma 3 and C gamma 4 genes at the mRNA level using solution hybridization. We have defined optimal conditions that allow the detection of picogram levels of IgG subclass specific mRNA, while keeping the cross-reactivity between the different probes below 2%. This approach will significantly facilitate studies aiming at characterizing the molecular mechanisms regulating the expression of the four human IgG heavy chain constant region genes.