Immunological measurement of transforming growth factor-beta 1 (TGF-beta1) in blood; assay development and comparison.

Development of a new, sensitive immunoassay for measuring transforming growth factor beta 1 (TGF-beta1) is described and compared with four commercially available TGF-beta1 immunoassays. Preanalytical conditions were evaluated. The nonlinearity found in serum or plasma is due to masking of TGF-beta1 by binding proteins in blood. Mixing TGF-beta1 with latency-associated peptide or alpha2-macroglobulin at physiological concentrations suppressed most of the TGF-beta1 signal. Plasma fibronectin showed no effect, even at concentrations exceeding its physiological range. Equilibrium concentrations computed from a model system confirmed the experimental results. Dilutional nonlinearity could be markedly reduced by an appropriately designed activation procedure that minimized the effects of reassociation between TGF-beta1 and its binding partners during restoration of a neutral pH. Plasma should be used for measuring TGF-beta1 in blood. Because serum TGF-beta1 is highly significantly correlated with the platelet count, probably most of the TGF-beta1 is released by platelet degranulation.