Protein radioisotopes

The conjugation of monoclonal antibodies (MoAbs) to radioisotopes, chemotherapeutic agents, and protein toxins has also been given consideration (65). Large amounts of human MoAbs can be produced by biotechnological means. 

When cells are suspended in a biological fluid or culture medium, both serum proteins and cells interact with the surface substrate. Serum protein adsorption behavior on SAMs has been examined with various analytical methods, including SPR [58-61], ellipsometry [13, 62, 63], and quartz QCM [64—66]. These methods allow in situ, highly sensitive detection of protein adsorption without any fluorescence or radioisotope labeling. SPR and QCM are compatible with SAMs that comprise alkanethiols. In our laboratory, we employed SPR to monitor protein adsorption on SAMs. 

This assay method (RIPA) is used primarily in research. It is too technically demanding for routine use in clinical laboratories. HIV is cultured in radio-labeled cells, or viral proteins are directly labeled with a radioisotope. The virus is disrupted and then exposed to the test specimen. Specific antigen-antibody complexes are concentrated and isolated by immunoprecipitation. After exten-... 

For many years, due to the availability and low cost of radioisotope-labeled secondary antibodies, radioactive detection was the method of choice in Western blotting. Newer methods that are less hazardous and easier to use, while maintaining comparable sensitivity, have been developed. Today, Western blotting detection methods can be light-based, (chemiluminescence, bioluminescence, chemifluorescence, and fluorescence), radioactivity-based, or color-based. It is important to note that the detection sensitivity depends on the affinity of the primary antibody for the antigen and on the affinity of the secondary antibody for the primary antibody and can therefore vary considerably from one protein sample to another and from one antibody batch to another. 

One other class of biochemical proteins that offers a similar advantage in clinical biochemistry is antibodies, which are highly specific for interaction with other proteins (i.e. with antigens) and bind with a high affinity. The combination of antibodies with radioisotopes produces very sensitive and very specific assays. This system has been used particularly for measuring the concentrations of hormones (see below) peptides and cytokines. 

Variations, which avoid the use of radioisotopes, are replacing RIA. Some utilize stable isotopes. However, 14C at such low levels that there is no radioactive waste can be coupled with accelerator mass spectrometry to provide very sensitive immunoassays.1 A great variety of other procedures are available. Some involve coupling to antibodies that carry fluorescent labels. Many are now automated. Often protein A from Staphylococcus aureus is utilized in various ways that take advantage of its ability to bind to the Fc portion of IgG from virtually all mammals. For example, it may fix antibodies to a surface or to a label)... 

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