Antigenic Determinants Reacting with Antibody

B-cell determinants or haptenic determinants, as they are frequently called, are comparatively well defined with regard to dimensions and specificity relationships. The problem of their size has attracted considerable interest during the last two decades and seems now satisfactorily elucidated. A recent careful review of these aspects has been provided by Goodman (1975). It has been known for some time that haptenic groups such as DNP and BPO do not comprise the entire deter- 

Parameters B-lymphocytes (from bursa of Fabridus in birds or bursal equivalent ) T-lymphocytes (from thymus) 

Antigenic markers on cell membrane MBLA (mouse) Fc-receptor C3-receptor H-2/HL-A la 6, TL (mouse) H-2/HL-A la 

Inactivation by X-irradiation Sensitive Primed cells for helper effect, cytotoxic effect and cell-mediated immunity resistant unprimed cells sensitive 

Corticosteroid Sensitive 95% of thymocytes sensitive population of residual 5% resistant 

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Immunization with denatured DNA-MBSA gives rise to antibodies, often mainly of the IgM class, that react with single-stranded DNA but not with native DNA. The largest antigenic determinant for such antibodies is about the size of a pentanucleotide. When DNA with an unusual base, such as the glucosylated hydroxymethylcytosine of T-even phage, is used, the specificity is directed largely to the modified base and much more IgG may be produced.Similarly, when UV-irradiated DNA or photooxidized DNA is used, the modified bases of the lesions provide the major specificity determinants. - ... 

Precise information on antigenic determinants reactive in T-cell activation, delayed hypersensitivity, and other manifestations of cellular immunity is quite limited. What has clearly emerged, however, is the notion that B- and T-cells react normally or at least frequently to different determinants on the same molecule. The classical example is that of Gell and Benacerraf (1959), where heat-denatured proteins lost their capacity to react with antibody against the native protein, whereas delayed reactions could be provoked with either native or denatured antigen. This finding was open to at least two possible interpretations namely that cellular immunity has a broader specificity than antibody responses, or that the structural entities serving as determinants in humoral and cellular immunity are not the same. 

An IgG-antibody against an individual ribosomal protein binds specifically only to this protein in a ribosomal subunit. Since the antibody is divalent it can form a bridge between the identical proteins in two subunits, leading to a dimer that can be examined under Ae electron microscope. The location of the bound antibody on the subunit surface can be determined, defining the position of the antigenic determinant of a particular protein. The method relies on the fact that IgG-antibodies are able to react with specific proteins within the intact ribosomal subunits and that both subunits have discernible shapes with recognizable morphological landmarks. 

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... 

The degree of specificity of the MAB may also present other disadvantages in assay development for some antigens. For instance, MABs to viral strains may be so specific that they do not cross-react with other minor strains of the same virus. The mixed response of polyclonal antibodies is likely to be directed to several antigenic determinants, one or more being present on each strain. 

Because MIB-1 monoclonal antibody is used extensively to determine the cell proliferation index, its applications are discussed below. This antibody detects the nuclear antigen Ki-67 expressed in proliferating cells but not in resting cells. The antibody reacts with the nuclei of cells in mid-Gj (first gap), S (DNA synthesis), G2 (second gap), and M (mitosis) phases, but not in the G0 or quiescent phases. The use of MIB-1 antibody is one of the simplest and most reliable labeling techniques for assessing the rate of proliferation of a neoplastic cell population. Thus, the antibody can be used to assess the growth fraction (i.e., the number of cells in cell cycle) of normal, reactive, and neoplastic tissues. 

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