Trends in the localization of bacterial antigens by immunoelectron microscopy

Transfusion-associated bacterial sepsis

The incidence of sepsis caused by transfusion of bacterially contaminated blood components is similar to or less than that of transfusion-transmitted hepatitis C virus infection, yet significantly exceeds those currently estimated for transfusion-associated human immunodeficiency and hepatitis B viruses. Outcomes are serious and may be fatal. In addition, transfusion of sterile allogenic blood can have generalized immunosuppressive effects on recipients, resulting in increased susceptibility to postoperative infection. This review examines the frequency of occurrence of transfusion-associated sepsis, the organisms implicated, and potential sources of bacteria. Approaches to minimize the frequency of sepsis are discussed, including the benefits and disadvantages of altering the storage conditions for blood. In addition, the impact of high levels of bacteria on the gross characteristics of erythrocyte and platelet concentrates is described. The potentials and limitations of current tests for detecting bacteria in blood are also discussed.

Immunogold labelling in combination with cryoultramicrotomy, freeze-etching, and label-fracture

During the past years, the methods of ultrastructural visualization of intracellular and cell-surface proteins have been improved considerably, mainly as the result of the development of low-temperature preservation in combination with immunocytochemical labelling procedures using poly- or monoclonal antibodies. In this contribution we will discuss the combination of immunogold labelling with cryoultramicrotomy and two replica methods, i.e. freeze-etching and label-fracture. The main advantage of cryoultramicrotomy is that it enables post-sectioning labelling, thus providing complete accessibility of all cellular antigens, located both intracellularly and on the cell surface. Important parameters that influence the labelling (i.e. label-efficiency), including penetration of the label and antibodies in the section, effects of fixatives on antigenicity, and steric hindrance, will be discussed in detail. The replica methods have the advantage of enabling an analysis of the lateral distribution of antigens located at the cell surface. The label efficiency is of particular importance in these studies and in this context several parameters will be discussed, including accessibility and effect of fixatives.

Immunoelectron microscopic studies on spore coat proteins of Bacillus megaterium

An immunochemical staining technique for the spore coat proteins of Bacillus megaterium ATCC 12872 was developed using colloidal gold as a second antibody. For reducing the non-specific immunogold binding and increasing the specific binding, the affinity-purified IgG was used as a first antibody. In sporulating cells at t10, gold particles were found not only in the spore coat but also in the mother cell cytoplasm, suggesting that some coat proteins were synthesized in the cytoplasm. Use of the specific affinity-purified antibody to 48K-protein demonstrated that this protein was one of the components of the outer coat.

Immunocytochemical demonstrations of cytoplasmic and cell-surface EGF receptors in A431 cells using cryo-ultramicrotomy, surface replication, freeze-etching and label fracture

In this paper we describe the use of a number of complimentary methods to visualize cytoplasmic and cell-surface located epidermal growth factor (EGF) receptors in cultured A431 cells. Cryo-ultramicrotomy in combination with immuno-gold labelling will be shown to provide an excellent method in visualizing cytoplasmic located EGF receptors in addition to cell-surface located EGF receptors. An important aspect in this method involves the possible effects of the fixatives on antigenicity. Using radioactive labelled anti EGF receptor antibodies, it was shown that formaldehyde as a fixative had no significant effect on label-efficiency. The density and lateral distribution of EGF receptors at the cell surface has been studied by three methods, i.e. surface replication, freeze etching and label fracture, all methods in conjunction with immuno-gold labelling. These methods allow in principle a quantitation of the surface distribution of the EGF receptors. The surface-replication method involves, however, dehydration and critical-point drying steps, and using radioactive labelled anti EGF receptor antibodies it was shown that in particular OsO4 fixation and dehydration caused a significant loss of cell-associated antibodies. This disadvantage is overcome by freeze etching and the label-fracture method, and as such these techniques provide the best methods for quantitative analysis of the planar distribution of cell-surface located EGF-receptors.

The use of ultrathin cryosections for localisation of influenza virus antigens in infected vero cell cultures

The localisation of influenza virus antigens in infected Vero cell monolayer cultures by post embedding immunoelectron microscopy requires both good resolution and the retention of antigenicity in the tissue sections. Ultrathin cryosections are superior to ultrathin resin sections for this purpose. The colloidal gold probe was used in conjunction with specific antibody preparations to localise three viral proteins. Antibody raised against haemagglutinin glycoproteins labelled the host cell membrane and the virus fringe without contamination of the host cell nucleus, whereas antibody raised against viral nuclear protein labelled throughout the host cell cytoplasm and nucleus. Matrix protein was localised within the nucleus and was associated with the host cell membrane of the infected cell. The appearance of all these proteins was maximal 24 h post infection.