DRB4 promoter polymorphism in DR7 individuals: correlation with DRB4 pre-mRNA and mRNA levels.

DRB genes encode proteins which play an important role in the immune response, and variation in their expression levels may be of functional immunological significance. To date, HLA class II gene promoter polymorphism has been analyzed almost exclusively in Epstein-Barr virus (EBV)-transformed B-cell lines. While previous studies have established important paradigms with regard to the mechanisms in DRB gene expression, the role of DRB4 promoter polymorphism in the variation of DRB4 expression levels, if any, is still unclear. We analyzed the effects of a previously described polymorphism in the promoter and 5' untranslated region of the DRB4 locus in peripheral blood mononuclear cells (PBMCs) from nine healthy DR7 individuals using the RNase protection assay. The RNase protection analyses showed that the location of transcription initiation is not affected. The DRB4 alleles show a threefold difference in pre-mRNA and a corresponding fivefold difference in mRNA levels in PBMCs. These data show that the DRB4 promoter polymorphism is associated with differential gene expression of this locus. The difference in pre-mRNA levels is directly affected by this DRB4 promoter polymorphism. The additional difference in mRNA levels is the result of post-transcriptional regulation. Therefore, the DRB4 promoter polymorphism may explain the previously observed variation in HLA class II DRB4 gene expression levels among different healthy DR7 individuals.