Figure 2

Localization of cysteine cathepsins in human thyroid tissue. Multi-channel fluorescence (A-D and insets), single channel and corresponding phase contrast micrographs (black and white) of cryo-sections taken from human thyroid tissue that were immunolabeled with antibodies directed against cysteine cathepsins B, K, L, or S in different combinations, as indicated. Co-localization is displayed by yellow signals as a result of overlapping red and green signals for either antibody labeling. Cathepsins B and K as well as K and L were mainly co-localized to the same intracellular compartments (B and D, insets, arrows), whereas cathepsin S was found in structures that were lacking other cysteine cathepsins (A and C, insets, arrows). Likewise, vesicles containing only cathepsin L or K (A and C, insets, arrowheads) were also prominent. All cysteine cathepsins were present within the Tg-containing extracellular follicle lumen (asterisks, Tg) where no co-localization of either cysteine cathepsin with one another was detectable. Cathepsins K and L were further detected in association with the apical plasma membrane of thyrocytes (B and C, insets, arrowheads). Bars represent 50 μm.