Fibroblasts were grown to confluence in 10‐cm tissue culture plates. Subsequently, the cell layers were washed with PBS. Then, each plate was filled with 7 mL of fresh DMEM medium containing 40 µg/mL of l‐ascorbic acid phosphate magnesium salt n‐hydrate. Fibroblasts from each patient were cultured with or without 10 ng/mL of TGFβ1. At defined time points, 50‐µL samples were withdrawn from the media. Subsequently, the samples were processed for polyacrylamide electrophoresis. Procollagen I present in cell culture media was detected by QWB with the anti‐pro‐α1(I) chain primary antibody, as described.20 Signal intensities of protein bands corresponding to intact and partially processed procollagen α1(I) chain were measured. Subsequently, results were normalized to the 1‐h data point. Normalized data were plotted against time and fitted to the linear model (GraphPad Prism, version 6.07; GraphPad Software Inc.). The slopes of the fitted curves represented an hourly rate of secretion of procollagen I. The significance of differences between the (+)TGFβ1 and the (−)TGFβ1 groups was analyzed using GraphPad Prism, version 6.07. We expressed the procollagen secretion rates in arbitrary units (au)/h.