Other Immunoassays

Spin immunoassay is also a type of homogeneous immunoassay. A change in the electron spin resonance (ESR) spectrum of a spin (marker)-labeled 

For many years, antigen-antibody reactions have been studied by agglutination techniques using red cells or latex particles which were coated with antigen or antibody. In this case, particles are regarded as a labeled marker. Descriptions of several methods that have been devised for detecting agglutination follow. 

In 1977, Cambiaso et al. (C4) showed that agglutination could be quantitatively measured by counting latex particles with a device designed for counting blood cells. The principle is based on the reduction of the total number of particles when they are agglutinated. 

Macromolecular substances with multiple antigenic determinant [Ag] can be determined by agglutination of particles which are coated with specific antibodies [Pa-Ab Ag Ab-Pa]. This method can detect immunoglobulins, human placental lactogens, a-fetoprotein, etc. The sensitivity is approximately 10 (xg/liter. Alternatively, antigen-coated particles are used these particles agglutinate with antibodies. Thus, antibodies can be determined by this system. Cambiaso et al. reported automated determination of immune complexes by their inhibitory effect on the agglutination of IgG-coated particles by rheumatoid factor or Clq (C3). 

The automated system of the particle counting immunoassay is now commercially available as the product impact (Immunoassay by Particle Counting), which can measure C-reactive protein, ferritin, human placental lactogen, thyroxine, a-fetoprotein (C7), IgE (M2), digoxin (C6), somatotropin (C5), and others. 

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Additionally it has been our experience that mass spectrometry as a routine detection/identification technique for bacteria is not well received by microbiologists and clinicians who prefer less expensive, less complicated approaches to bacterial typing and identification, such as methods based on polymerase chain reaction (PCR) and enzyme-linked immunosorbent assays (ELISA). For that reason we have adapted our MS approach to serve as a means of biomarker discovery that feeds candidate proteins or leads into development as PCR targets or other immunoassay techniques. 

The following sections briefly describe the principal enzymes used for conjugation with other protein molecules, particularly in the design of ELISA and other immunoassay systems. 

Other immunoassays are based on the same antibody-antigen binding reaction but use a different labeling system for detection. Instead of an enzyme label, there are radioactive isotopes, and fluorescent and luminescent labels. Some important immunoassays are defined below ... 

It is both encouraging and exciting to observe that the field of immunology has finally been directed toward plants and molecules of plant origin. For all of plant science, the future developments of the RIA, EIA and other immunoassays should aid greatly in solving some of our most troublesome problems. We are of the opinion that the immunoassay has the potential to become a major analytical tool in the citrus industry and in Table IV are listed just some of the areas where this procedure might be employed. 

Other Immunoassay Methods. Other immunoassay methods can be used to quantitate the hapten these include homogeneous enzyme... 

Comparison of a Radioimmunoassay for Plasma Testosterone Using Hydroxyapatite with Other Immunoassays Methods... 

The MAbs and EIA we have developed provide a means of detecting avermectins at the level of sensitivity now possible with HPLC and gas chromatography. The EIA employs standard methods, and it is stable, reproducible, and economical. The solvent tolerance exhibited by the MAbs makes the assay compatible with methods for recovering residues of these very hydrophobic compounds. Monoclonal antibodies have the well-known advantages of defined affinity, specificity, and potentially infinite supply. The IgGi subclass of all of the avermectin MAbs makes them easy to purify to near-homogeneity by well-documented methods. This could facilitate tests of their usefulness in other immunoassay formats. 

Specificity. The specificity of radioimmunoassays, like that of any other immunoassay, relies on the specific reaction between an antibody and an antigen. Since the identity of both is impossible to prove, the specificity must always be open to some doubt. The reaction of antibody with its antigen might be compared with that of an enzyme with its substrate thus ... 

Bounaud, M. P., Bounaud, J. Y., Bouin-Pineau, M. H., Ozget, L., and Begon, F., Chemiluminescence immunoassay of thyrotropin with acridinium ester-labeled antibody evaluated and compared with two other immunoassays. Clin. Chem. (Winston-Salem, N.C.) 33, 2096-2100... 

Another important consideration when using the ELISA (and other immunoassay formats) is the cross-reactivity of the method. Cross-reactivity (CR) can be described as the interaction between an antigen and an antibody, which was generated against a different but similar antigen. The cross-reactivity profile should be characterized during the validation of a new immunoassay. The cross-reactivity. 

Other immunoassays No fluorogenic reaction is needed if the radiolabel or the enzyme label is replaced by a fluorogenic label, which can be measured after the bound-free separation. An example of such a label is 4-methylumbelliferone 3-acetic acid. The advantage of these fluoroimmunoassay methods (FIA) is their simplicity. However, a disadvantage is that, as a consequence of the strong background fluorescence, the sensitivity is poor. 

The immunometric-type assay has also been adapted for use with nonisotopic labels and is typically carried out in a heterogeneous format in which the antibody is immobilized on a solid support, such as a microtiter dish, membrane, or collection of beads. The canonical clinical immunoassay format in toady s laboratories is the enzyme-linked immunosorbent sandwich assay, which employs two antibodies, one to capture the analyte and the other to detect and quantify it. More details of the principles of these and other immunoassay techniques are given elsewhere in this encyclopedia. 

Other biological assays have been developed that avoid the sacrifice of animals. The mouse neuroblastoma assay measures PSTs by the survival of cultured neuroblastoma cells after addition of extract. In this assay, Na /K -ATPase inhibitor ouabain and the sodium channel activator verattidine are added to neuroblastoma cells prior to the addition of toxin extract. PSTs that are present in the extract prevent the veratridine-induced influx of sodium ions into the cells, and thus prevent cell death. A commercially available kit version of this assay, the MIST shippable cell bioassay kit [184], showed good agreement in a comparative study to the mouse bioassay [185] however, it performed unsatisfactorily in an AOAC international collaborative study in 1999, and there have been quality problems related to the shipping of the kit. The MIST kit was eventually replaced by the MIST Alert kit, which is an immunological assay that utilizes antibodies to STX, neoSTX, GTXl-4 [186]. Various other immunoassays exist [187]. 

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