Immunocomplex

In type III or immunocomplex-mediated allergy, IgG antibodies form complexes with antigen. At low exposures, the body is able to remove diese complexes, but if there is a severe exposure, immunocomplexes release a variety of proinflammatory cytokines. The involvement of this mechanism is clearest in serum sickness. This mechanism is also considered to be most important in the development of extrinsic allergic alveolitis (hypersensitivity pneumonitis, especially... 

In amperometry, the current produced by the oxidation or reduction of an electroactive analyte species at an electrode surface is monitored under controlled potential conditions. The magnitude of the current is then related to the quantity of analyte present. However, as both antibody and antigen are not intrinsically electroactive, a suitable label must be introduced to the immunocomplex to promote an electrochemical reaction at the immunosensors. In this respect, enzyme labels including the... 

The development of electrochemical immunosensors generally involves the immobilization of an immunocomplex on a single electrode, followed by detection via the... 

Very often, the electrode-solution interface can be represented by an equivalent circuit, as shown in Fig. 5.10, where Rs denotes the ohmic resistance of the electrolyte solution, Cdl, the double layer capacitance, Rct the charge (or electron) transfer resistance that exists if a redox probe is present in the electrolyte solution, and Zw the Warburg impedance arising from the diffusion of redox probe ions from the bulk electrolyte to the electrode interface. Note that both Rs and Zw represent bulk properties and are not expected to be affected by an immunocomplex structure on an electrode surface. On the other hand, Cdl and Rct depend on the dielectric and insulating properties of the electrode-electrolyte solution interface. For example, for an electrode surface immobilized with an immunocomplex, the double layer capacitance would consist of a constant capacitance of the bare electrode (Cbare) and a variable capacitance arising from the immunocomplex structure (Cimmun), expressed as in Eq. (4). 

As the immunocomplex structure is generally electroinactive, its coverage on the electrode surface will decrease the double layer capacitance and retard the interfacial electron transfer kinetics of a redox probe present in the electrolyte solution. In this case, Ra can be expressed as the sum of the electron transfer resistance of the bare electrode CRbare) and that of the electrode immobilized with an immunocomplex (R immun) ... 

There are several ways to present the Faradaic impedance data obtained at an electrode immobilized with an immunocomplex in the presence of a redox probe. For example, ZIm is plotted vs ZRe as a function of decreasing frequency to obtain a... 

There are mainly three types of transducers used in immunosensors electrochemical, optical, and microgravimetric transducers. The immunosensors may operate either as direct immunosensors or as indirect ones. For direct immunosensors, the transducers directly detect the physical or chemical effects resulting from the immunocomplex formation at the interfaces, with no additional labels used. The direct immunosensors detect the analytes in real time. For indirect immunosensors, one or multiple labeled bio-reagents are commonly used during the detection processes, and the transducers should detect the signals from the labels. These indirect detections used to need several washing and separation steps and are sometimes called immunoassays. Compared with the direct immunosensors, the indirect immunosensors may have higher sensitivity and better ability to defend interference from non-specific adsorption. 

At the end of the incubation pulse, spin the tube to pellet the immunocomplex. 

JP Ou, STH Chang, WSB Yeung. Separation of bovine serum albumin and its monoclonal antibody from their immunocomplexes by sodium dodecyl sulfate-capillary gel electrophoresis and its application in capillary electrophoresis-based immunoassay. J Chromatogr B 731 389—394, 1999. 

Immunosensors can be classified into two broad categories non-labelled and labelled. Non-labelled immunosensors are designed in such a way that the immunocomplex i.e. the antigen-antibody complex) is directly determined by measuring the physical changes induced by the complex formation. In contrast, labelled immimosensors include a sensitively detectable label, so the inmumocomplex is determined by measuring the label. 

Non-labelled immunosensors rely on various principles (Fig. 3.27.A). Either the antibody or the antigen is immobilized on the solid matrix to form a sensing device. The solid matrix should be sensitive enough at the surface to detect immunocomplex formation. Electrode, membrane, piezoelectric and optically active surfaces may in principle be used to construct non-labelled immunosensors. The antigen or antibody to be determined is dissolved in a solution and reacted with the complementary matrix-bound antibody or antigen to form an immunocomplex that alters the physical e.g. the electrode potential or intrinsic piezofrequency) or optical properties of the... 

Much research has gone into raising the sensitivity and selectivity of immunosensors to the desired levels. Several labels have proved to ensure a high sensitivity, yet radioisotopic labels have essentially been avoided. Non-isotopic labels for immunosensors include various enzymes, catalysts, fluorophores, electrochemically active molecules and liposomes. Labelled immunosensors are basically designed so that immunochemical complexation takes place on the surface of the sensor matrix. There are several variants of the procedure used to form an immunocomplex on the matrix. In the final step, however, the label should always be incorporated into the immunocomplex for determination, as shown in Fig. 3.27.B. 

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