Fibroblast cells with endocytosed particles

Fibroblast cells in culture. This image is a composite of a phase contract image and a fluorescence microscopy image. The nuclei are stained blue with DAPI and the red spots are 0.02 micron fluorescent spheres that have been taken up into the cytoplasm of the cells by the process of endocytosis. The phase contrast image enables the cell outlines to be visualised.