Immunogold labeling of cryosections from high-pressure frozen cells

Immunogold labeling of cryosections according to Tokuyasu (Tokuyasu KT. A technique for ultracyotomy of cell suspensions and tissues. J Cell Biol 1973;57:551-565), is an important and widely used method for immunoelectron microscopy. These sections are cut from material that is chemically fixed at room temperature (room temperature fixation, RTF). Lately in many morphological studies fast freezing followed by cryosubstitution fixation (CSF) is used instead of RTF. We have explored some new methods for applying immunogold labeling on cryosections from high-pressure frozen cells (HepG2 cells, primary chondrocytes) and tissues (cartilage and exocrine pancreas). As immunolabeling has to be carried out on thawed and stable sections, we explored two ways to achieve this: (1) The section fixation method, as briefly reported before (Liou W et al. Histochem Cell Biol 1996;106:41-58 and Möbius W et al. J Histochem Cytochem 2002;50:43-55.) in which cryosections from freshly frozen cells were stabilized in mixtures of sucrose and methyl cellulose and varying concentrations of glutaraldehyde, formaldehyde and uranyl acetate (UA). Only occasionally does this method reveal section areas with excellent cell preservation and negatively stained membranes like Tokuyasu sections of RTF material. (Liou et al.) (2) The rehydration method, a novel approach, in which CSF with glutaraldehyde and/or osmium tetroxide (OsO4) was followed by rehydration and cryosectioning as in the Tokuyasu method. Especially, the addition of UA and low concentrations of water to the CSF medium favored superb membrane contrast. Immunogold labeling was as efficient as with the Tokuyasu method.