Comparison of antibody secretion efficiency of different P. tricornutum transfectants. In a small scale screening twelve independent transfectants were tested for antibody expression and secretion efficiency after two days of protein expression. Proteins of the cellular fraction (c) and the cell-free medium (m) were precipitated and separated by SDS-PAGE. Western Blot analyses demonstrate that except for cell line #4 all transfectants express the antibody and secrete it efficiently into the medium. Cell lines #3, #8, #11 and #12 were selected four broader analyses on antibody functionality and quantity. As a loading control for cellular proteins and to check that the medium is not contaminated with intracellular proteins of destroyed cells an antibody against α-tubulin was used. 10 μg protein of the cellular fraction and protein of 15 ml cell-free medium were loaded.