Enzyme-linked immunosorbent interactions

Liposome conjugates may be used in various immunoassay procedures. The lipid vesicle can provide a multivalent surface to accommodate numerous antigen-antibody interactions and thus increase the sensitivity of an assay. At the same time, it can function as a vessel to carry encapsulated detection components needed for the assay system. This type of enzyme-linked immunosorbent assay (ELISA) is called a liposome immunosorbent assay or LISA. One method of using liposomes in an immunoassay is to modify the surface so that it can interact to form biotin-avidin or biotin-streptavidin complexes. The avidin-biotin interaction can be used to increase detectability or sensitivity in immunoassay tests (Chapter 23) (Savage et al., 1992). 

The model immunoassay is the enzyme-linked immunosorbent assay (ELISA) in which a non-specific capture antibody is bound to a surface, such as a multi-well plate or small tube [13]. In the basic form of ELISA, a second antibody tagged with an enzyme interacts specifically with the analyte. The enzyme assay produces a colored product that is read with a spectrophotometer. There are many variations on the basic immunoassay format that serve to increase sensitivity, specificity, linear range, and speed. Many commercial instruments have been developed to take advantage of various technologies for reporter molecules. The immunoassay may be coupled to an electronic sensor and transducer, such as a surface acoustical wave (SAW) sensor. Electrochemiluminescence (ECL) is a method in which the detector antibody is tagged with a ruthenium-containing chelate [13-15]. When the tag is... 

Enzyme-linked immunosorbent assay (ELISA) is a new method in alkaloid studies. The application of ELISA to alkaloid study is based on antibody incubations. It differs from classical precipitation-based methods in that specific antigen-antibody interactions are recognized by assaying an enzyme label conjugated to one reactant, usually an antibody. Because of the sensitivity with which enzyme... 

The most predominant application of antibodies has been in the area of diagnostic assays, known as immunoassays, which exploits the specific interaction between the antibody and antigen. The world immunoassay market for clinical and food diagnostics, environmental analysis and other applications exceeded 1.2 billion in 1990. ELISA (Enzyme-Linked Immunosorbant Assay) represents 60% of that market (2). Annual growth rates have been projected at 10-15%. The food diagnostics is projected to grow to 500 million by the year 2000 (3). 

Fig. 10.10. Determination of thermogenin amount in brown adipose tissue mitochondria by the enzyme-linked immunosorbent assay (ELISA) system. The amount of thermogenin was determined as elsewhere described (Cannon et al. [13] Sundin et al. [40] Hansen et al. [56]) in an assay system based on the competition between absorbed and added thermogenin for rabbit on/r-rat-thermogenin antibodies. The interaction was followed with a sheep onri-rabbit-IgG antibody conjugated to alkaline phosphatase. The reaction was linearized as indicated (abs 0 is the absorbance developed in the absence of competing thermogenin). It is seen that this assay can detect less than 0.25 fig thermogenin, i.e., the content in less than 10 fig of mitochondria. It is also seen that the thermogenin content of rat brown fat mitochondria is approximately doubled after a 24 h cold stress. (Our unpublished observations.)...

On the basis of an enzyme thermistor, Mattiasson et al. (1977) developed one of the first immunosensors. Immobilized antibodies against albumin are placed in a column and set into an ET. After injection of an albumin-sample and a known amount of enzyme-labeled albumin, both are separated from the sample matrix by antibody-antigen-interaction. After injection of a substrate, the change in heat is a measure of analyte concentration. The less heat produced means that more albumin has been bound. An elution step regenerates the ELISA. Due to its thermal detection principle, the procedure is called TELISA (thermometric enzyme-linked immunosorbent assay). Figure 3 shows the principle of the TELISA procedure in its sandwich configuration. 

The release of different cytokines and chemokines is often measured in the supernatant of NM-exposed cells in order to estimate the pro-inflammatory potential of NMs. It is usually done using a reliable and very sensitive enzyme-linked immunosorbent assay (ELISA). Since the presence of NMs could interact with the optical readouts of ELISA, the cell supernatants are centrifuged to sediment the NMs. However, due to the high affinity of the different proteins to NM surface, also cytokines can adsorb on the particles and be removed during the centrifugation, so their production can be underestimated [59, 65]. 

Antibodies can be used for a variety of applications in the molecular characterization of receptors and receptor-hgand interactions. Antibodies can be used for the detection of receptors in tissue shces. Western blot experiments [48], or ELISAs (enzyme-linked immunosorbent assays) [49]. They can also be used in competition experiments to map the binding epitope of a hgand [50]. Even though the use of antibodies is routine, fhere is no general protocol for fheir generation. 

Many types of assay are available to be used in HTS protocols to identify inhibitors of PPIs, but a competition assay, in which inhibition of complex formation is measured, is most common. Fluorescence polarization (FPA), fluorescence resonance energy transfer (FRET), enzyme-linked immunosorbent assays (ELISA), and other assay formats have been used. The interacting proteins can be used in their full-length forms though, more frequently only the interacting domains are employed, and if possible the excised interacting peptide is usually preferred. 

Immunoassay techniques are based on the antigen-antibody interaction. These techniques involve a competitive reaction between antigen molecules of the target molecules and labeled antigen molecules for a limited number of antibodies. Enzyme-linked immunosorbent assays (ELISA) in which antibodies are immobilized on a solid phase are the most popular for pesticide detection. As pesticides are small molecules, in order to synthesize antibodies, pesticide derivatives (haptens) must be synthesized and coupled to carrier proteins. ... 

The antagonistic effect of all 25 candidate compounds on LFA-l/ICAM-1 binding was tested in a competition enzyme-linked immunosorbent assay (ELISA). One weakly active compound was identified that blocked the interaction with an IC50 value of 70 [xM (compound 6). This compound was identified by similarity searching. 

Purity for a small molecule is a relatively simple concept. Normally, an HPLC method is sufficient to measure the content and impurity levels of a small molecule drug. A macromolecule, such as a protein, has a much more complex behavior. Determining protein concentration by UV absorption spectroscopy can give a measure of the total protein in the product, but it will not necessarily differentiate between active protein and inactive protein (i.e., denatured or otherwise degraded). A validated method or methods to determine the biological activity of the molecule is needed. So, whereas protein concentration is usually tested as part of the specifications, it is also normally accompanied by one or more methods that measure or correlate to biological activity. This is the bioassay. These methods can be animal-based or cell-based, protein interaction assays, binding methods such as surface plas-mon resonance or ELISA (enzyme-linked immunosorbent assay) and immunoblot methods. 

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