Thyroid follicles are composed of a stratum of epithelial cells and contain a colloid rich in thyroglobulin. The protein plays an important role in the production of thyroxine. Blood tests are available that can measure the level of thyroglobulin in the body, and these tests are particularly useful for certain cancer patients. Individuals with active thyroid cancer may exhibit unusually high levels of the protein. Following successful surgical removal of the thyroid, thyroglobulin should no longer be detectable. Consequently, thyroglobulin testing can reveal whether or not all thyroid cancer cells have been eliminated.

The section of rat thyroid tissue featured in the digital image above was labeled with Oregon Green 488 conjugated to wheat germ agglutinin, a lectin that selectively binds to sialic acid residues found in both mucoproteins and glycoproteins. The cells were also stained with Alexa Fluor 568 conjugated to phalloidin and the dye Hoechst 33342, which target the cytoskeletal filamentous actin network and nuclear DNA, respectively. Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.