It is well known that IgA isotype switching is induced by TGF-β1. LPS-activated mouse normal B cells well differentiate into IgA secreting plasma cells under the influence of TGF-β1. Nevertheless, there are lots of difficulties in studying normal B cells in detail because it is not simple to obtain highly purified B cells, showing low reproducibility and transfection efficacy, moreover impossible to keep continuous culture. To overcome these obstacles, it is desperately needed to develop B cell line which acts like normal B cells. In the present study, we investigated whether CH12F3-2A lymphoma cells are appropriate for studying IgA isotype switching event.

CH12F3-2A B cell line was treated with LPS and TGF-β1, then levels of germ-line (GL) transcripts were measured by RT-PCR, and GLα promoter activity was measured by luciferase assay. In addition, membrane IgA (mIgA) expression and IgA secretion were determined by FACS and ELISA, respectively.

TGF-β1, regardless of the presence of LPS, increased level of GLα transcripts but not GLγ2b transcripts. However, IgA secretion was increased dramatically by co-stimulation of LPS and TGF-β1. Both mIgA and IgA secretion in the presence of TGF-β1 were further increased by over-expression of Smad3/4. Finally, GLα promoter activity was increased by TGF-β1.

CH12F3-2A cell line acts quite similarly to the normal B cells which have been previously reported regarding IgA expression. Thus, CH12F3-2A lymphoma cell line appears to be adequate for the investigation of the mechanism(s) of IgA isotype switching at the cellular and molecular levels.