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KMID : 0578319960060060746
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Molecules and Cells
1996 Volume.6 No. 6 p.746 ~ p.752
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Characterization of Mutated Transforming Growth Factor-β1 Transformants and Its Modulatory Effect on IgA Isotype synthesis by Murine B Lymphocytes
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Rhee, Ki Jong
Nham, Sang-Uk/Yoo, Jin-Su/Yie, Se Won/Chun, Gie-Teak/Choi, Eui Yul/Park, Joo-Hung
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Abstract
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Transforming growth factor-βl (TGF-βl ) is a pleiotropic cytokine having both inhibitory and stimulatory effects on the differentiation of a variety of cell types. In the context of Bcell differentiation, it has been shown that purified TGF-βl increases IgA isotype switching by murine and human B cells in vitro. However, it has not been formally accepted whether TGF-βl is actually an important inducer of IgA synthesis in vivo. In addition, it is difficult to evaluate the autocrine and paracrine effect because endogenous TGF-βl issecreted not only in small amounts but in an inactive form. As a first step in understanding the role of TGF-βl in induction of IgA synthesis in vivo, CHO cells were stably transfected with mutated TGF-βl cDNA under the control of a metallothionein promoter, and the biological function of the expressed proteins was characterized in a variety of ways. TGF-βl -transfected CHO cells (TT-CHO cells) induced by zinc sulfate without any artificial activation were found to secrete at least 5,000 pg/ml as measured by ELISA. In addition, the secreted TGF-βl adhered to soluble type Ⅱ TGF-βl receptors. A bioassay using Mv1Lu cells showed that the supernatant from TT-CHO cells retained not less than 8,000 pg/ml of TGf-βl, confirmed by a blocking experiment with anti-TGF-βl antibody. These results indicate that the mutated recombinant TGF-βl expressed from TT-CHO cells is fully biologically active. We were then interested in the effect of the produced rTGF-βl on IgA isotype synthesis by mouse spleen B cells. The TT-CHO cell supernatant, in combination with rIL-2, substantially increased IgA isotype production. Finally, LPS-activated murine spleen B cells were transfected transiently with mutated TGF-βl cDNA, resulting in IgA isotype induction. Our results suggest that B cell transfectants produce rTGF-βl in an active form that can modulate its own differentiation in an autocrine fashion.
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