Transcriptional regulation of the Iγ2 promoter in Human B cells

Abstract

Human IgG2 (immunoglobulin G2) is the predominant IgG subclass that is expressed in response to bacterial capsular polysaccharides. An IgG2 deficiency can therefore result in compromised immunity to carbohydrate antigens. Expression of IgG antibodies require an intramolecular recombination event that is preceded by transcription from intragenic (I) promoters. Thus, generation of IgG2 antibodies requires the induction of the Iγ2 promoter. To elucidate the regulation of the Iγ2 promoter in response to T cell contact and cytokine signals, deletion constructs were made to test the role of sequences within the Iγ2 proximal promoter in response to CD40 activation and stimulation with IL-4. Upon transient transfection into Ramos 2G6 cells (an IgM⁺ Burkitt's lymphoma cell line), we found that truncation of the distal 228 bp caused a considerable decrease in basal and induced expression in response to these signals. Site-specific mutagenesis of this region supported this finding. This data implicates a region containing an NF-κB site in the Iγ2 proximal promoter as a major regulator of transcriptional activity and provide a starting point to investigate further how this promoter is regulated.