Immunodetection and quantitation of the two forms of transforming growth factor‐beta (TGF‐β1 and TGF‐β2) secreted by cells in culture

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Abstract
Transforming growth factor beta (TGF-β), a potent modulator of cell growth, differentiation, and the expression of extracellular matrix components in a variety of cell types, exists as two distinct homodimers (TGF-β1 and TGF-β2), sharing 71% sequence homology. Radioreceptor and previously described radioimmunological assays using rabbit antibodies have not been able to distinguish between these two forms. We have developed antisera in turkeys against native TGF-β1 and TGF-β2, each of which specifically blocks both the receptor binding and biological activity of each of these peptides. With these immunological reagents we describe sensitive and specific immunological assays for TGF-β1 and TGF-β2 in complex biological fluids. Using these assays we show that both TGF-β1 and TGF-β2 are secreted by a variety of cultured cells, but that some cells secrete predominantly either TGF-β1 or TGF-β2 while others secrete both peptides in nearly equal amounts. Our results demonstrate that the expression of each of the two forms of TGF-β is independently regulated.