Figure 5.

Production of bioactive TGF-β by murine plasmacytomas. Cell-free supernatants from 24-h cultures of plasmacytomas (T1165 and T2027 shown here) and ascites removed from mice bearing the plasmacytoma MOPC467 were diluted and added to cultures of TGF-β-sensitive mink lung epithelial cells (CCL64 cells). A 1:3 dilution of each resulted in an inhibition of CCL64 cells ≥ 0.125 ng/ml TGF-β1. Inhibitory activity present in 1:12 dilutions could be reversed specifically by the addition of the monoclonal anti-TGF-β antibody 1D11. The substantial increase in this specific activity after heat activation of culture supernatants indicated that they produced a mixture of active and latent forms. This difference was less pronounced in ascites samples, suggesting that other mechanisms may be contributing to activation of TGF-β in vivo.