FLSSM applied to different products and cell lines. A, A' and C: transmitted light images. A and B: colonies from CHO-tPA transfectant pool. B: detection of secreted tPA using an anti-tPA antibody conjugated to Alexa488 in semi-solid medium. Note the presence of positive and negative colonies in the same field. Arrow indicates positive, high-producing clone; A': insert blown up from A showing that a precipitate around the positive colony is visible in transmitted light microscopy. C and D: colony from 293-IGF-E5 transfectant pool. D: detection of secreted IGF-E5 (small fluorescent dots at the colony periphery using an anti-His Tag antibody conjugated to FITC in semi-solid medium).