Processing tissue and cells for transmission electron microscopy in diagnostic pathology and research

In transmission electron microscopy (TEM), electrons are transmitted through a plastic-embedded specimen, and an image is formed. TEM enables the resolution and visualization of detail not apparent via light microscopy, even when combined with immunohistochemical analysis. Ultrastructural examination of tissues, cells and microorganisms plays a vital role in diagnostic pathology and biologic research. TEM is used to study the morphology of cells and their organelles, and in the identification and characterization of viruses, bacteria, protozoa and fungi. In this protocol, we present a TEM method for preparing specimens obtained in clinical or research settings, discussing the particular requirements for tissue and cell preparation and analysis, the need for rapid fixation and the possibility of analysis of tissue already fixed in formalin or processed into paraffin blocks. Details of fixation, embedding and how to prepare thin and semi-thin sections, which can be used for analysis complementary to that performed ultimately using TEM, are also described.