Measurement of Latent TGF-β1 could theoretically be achieved using a mAb
to LAP and a mAb to TGF-β1. However, although a panel of mAbs was obtained from the Latent TGF-β1-immunized mice herein, all mAbs recognized Selleck GSK3 inhibitor the LAP entity. This implies that TGF-β1, in the latent complex, is poorly accessible for antibodies. A limited accessibility of TGF-β1 in its latent form was also indicated by the finding that the mAbs to LAP could not be combined with any of various commercially available antibodies to TGF-β1, to create a functional ELISA for Latent TGF-β1 (unpublished data). A limited availability of TGF-β1 is obviously also the reason for why Latent TGF-β1 needs to be dissociated in order to measure total TGF-β1. The total TGF-β1 buy Tyrosine Kinase Inhibitor Library plasma levels measured by TGF-β1 ELISA herein, were in accordance with expected levels. The average total TGF-β1 levels in plasma from healthy control cohorts differs between studies but is generally between 40 and 800 pM (approximately 1–20 ng/ml) although both higher and lower levels are reported (Kropf
et al., 1997 and Sundman et al., 2011). The rather large variation of total TGF-β1 levels found in different studies using plasma from control subjects can to a large extent be ascribed to the method used for sample preparation, known to have a great impact on the resulting levels of total TGF-β1 (Walther et al., 2009). In studies aiming to quantify TGF-β1 levels in the blood, measures are often taken to eliminate platelets as they otherwise can release high levels of Latent TGF-β1 during sample preparation (Walther et al., 2009). For this reason, plasma is preferred over serum but many studies nevertheless use serum samples with high levels of total TGF-β1 measured as a result. In this respect there is no difference
between measuring total TGF-β1 by TGF-β1 ELISA or Latent TGF-β1 AZD9291 price by LAP ELISA; samples prepared such that it results in platelet activation will yield high levels irrespective of the method used for analysis. The choice of anti-coagulants used to obtain plasma has been reported to have an impact on the total TGF-β1 level as well (Walther et al., 2009). This was also indicated by the finding herein that lower levels of latent TGF-β1 was detected in citrate plasma samples compared to heparin and EDTA plasma. Also the plasma levels of free TGF-β1 vary between studies but are in general substantially lower than the total TGF-β1 levels, if detectable at all (Hellmich et al., 2000 and Walther et al., 2009). In the plasma analyzed herein, free TGF-β1 corresponding to 0–1.5% of the total TGF-β1 was found. Culture supernatants of human monocytes and other cell types have also been reported to primarily contain Latent TGF-β1 and little free TGF-β1 (Flaumenhaft et al., 1993, Lawrence, 2001 and Twardzik et al., 1990).