Antigen-specific reactions

Antigen-specific reactions involving T cells, (a) Killer T cells interact and destroy target cells that display complexes of processed antigen with an MHC I protein. Effective interaction requires that the TCR... 

Although there is no direct evidence that molecular structure and gelation properties show such a close correlation, this hypothesis may help to show that the mechanism of gelation is a very specific reaction analogous to specific biochemical reactions, like antigen-antibody reactions, etc., in which polysaccharides are also involved. 

Immobilization techniques have been applied in the preparation of immobilized CL reagents, with specific advantages such as reusability, improved stability, and increased efficiency. These strategies have been applied in the development of CL sensors, which today constitute the most important tools in analytical chemistry because of the high sensitivity offered. Optical fibers have been used to transfer light in order to improve the quality of detection, and new types of flow-through cells have been introduced in the construction of CL sensors. Also, selectivity has been considerably improved by the utilization of enzymatic or antigen-antibody reactions. 

A classical approach is the enzyme linked immunosorbent assay (ELISA), where the antigen (e.g., the protein to be quantified) is immobilized on the surface of a well. A first antigen-specific antibody is applied to occupy all antigens, before a second antibody binds all primary antibodies on the well. The second antibody carries an enzyme, which now catalyzes a color reaction. If the substrate of the enzyme is given in high excess, the enzyme is saturated and the production of product is linear with time and concentration of second antibody and antigen (Fig. 8). 

Biedermann, T. et al, Reversal of established delayed type hypersensitivity reactions following therapy with IL-4 or antigen-specific Th2 cells. Eur. J. Immunol., 31, 1582, 2001. 

Immunochemical techniques are based on the immunological reaction derived from the binding of the antibody to the corresponding antigen. This reaction is reversible and is stabilized by electrostatic forces, hydrogen bonds, and Van der Waals interactions. The formed complex has an affinity constant (k j that can achieve values around the order of 1010 M. This great affinity and specificity between the specific antibody and the antigen (or the analyte) have turned these techniques into powerful analytical tools to detect and quantify... 

The specificity of antibodies can be exploited in order to probe the in situ organization of cells and tissues. Cellular antigens can be identified both in viable cells and in frozen or fixed tissue sections. Antibodies are used to identify the appropriate antigen in the section and then the position of this primary antibody may itself be detected either directly if it was initially labelled or indirectly using another secondary antibody or molecule to attach to the antibody (Figure 7.8). Samples need to be carefully washed after addition of the primary or labelled antibody in order to prevent any non-specific reactions. Labels that have been successfully linked to antibodies include the following ... 

Enzyme-linked immunosorbent assay (ELISA) is based on the specific reaction between an antibody and an antigen. One of the reagents in the reaction is labeled with an enzyme that generates a colorimetric product that can be measured with a spectrophotometric device. The color intensity correlates with the concentration of specific antibody and the respective antigen. The reaction can be formatted in various ways in a multiwell plate (microtiter plate) with the common formats being the sandwich assay, the competitive assay, and the direct assay. (See Figure 11.1.)... 

Aqueous extracts of cotton dust and cotton bract induced the formation of specific precipitating antibodies in rabbits. The antisera cross-reacted with both extracts as well as with extracts of cotton stem, leaf, and burr, baled cotton and gin trash. Cross-reactivity was also demonstrated with extracts of flax, soft hemp, sisal, and jute. No antigen-antibody reaction was obtained with extracts of cottonseed hulls, cottonseed proteins, noncontami-nated cotton lint, or house dust. No reaction was obtained between the antisera to dust and several connmercial preparations of bacterial lipopolysac-charides believed to be present in cotton dust. 

Figure 6. Antigen-antibody reaction between the antisera specific for laccase m and laccases I and III.

The basis for this procedure is the antigen-antibody "reaction"—i e., specific binding of an antibody to the molecule being assayed. Among the many different immunoassay techniques that have been developed—e.g., radioimmunoassay (RIA), and chemoluminescence immunoassay (CIA)—a version of the enzyme-linked immunoassay (ElA) is shown here. 

The interaction of a chemical (hapten) with epidermal proteins (carrier) can result in a hapten-carrier complex capable of activating skin-associated lymphoid tissue (sensitisation) and dissemination of antigen-specific T l)unphocytes (induction). Subsequent encoimter with the same or cross-reactive chemicals can result in the elicitation of a characteristic inflammatory skin reaction. The clinical condition is referred to as allergic contact dermatitis and is characterised by erythema, oedema, vesiculation and pruritus. Allergic contact sensitisation is, therefore, classed as a cell-mediated immunological response to chemicals that contact and penetrate the skin. 

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