Binding to Antigen

A third elimination pathway occurs if anti-idiotype antibodies are formed as an immune response of the human body to the administration of mAbs. Following repeated administration, anti-idiotype antibodies are usually observed after one to two weeks, with the extent of the adverse reaction strongly depending on several factors  

The formed anti-idiotype antibodies almost irreversibly bind the therapeutic antibodies and therefore, by neutralization, eliminate them from the body. In total, the formation of anti-idiotype antibodies will alter the pharmacokinetics and consequently the pharmacodynamic effect (loss of effectiveness) of affected mAbs. 

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The goal of most protein modification or conjugation procedures is to create a stable product with good retention of the native state and activity. Ideally, any derivatization should result in a protein that performs exactly as it would in its unmodified form, but with the added functionality imparted by whatever is conjugated to it. Thus, an antibody molecule tagged with a fluorophore should retain its ability to bind to antigen and also have the added functionality of fluorescence. 

Figure 7.21 Dendrimers that are fluorescently labeled as well as biotinylated create enhanced detection reagents for use in (strept)avidin-biotin-based assays. Large complexes containing multiple fluorescent dendrimers can bind to antigens and form a highly sensitive detection system that exceeds the detection capability of fluorescently labeled antibodies.

In some cases, the preparation of a fluorescently labeled antibody is not even necessary. Particularly, if indirect methods are used to detect antibody binding to antigen, then preparing a fluorescently labeled primary antibody is not needed. Instead, the selection from a commercial source of a labeled secondary antibody having specificity for the species and class of primary antibody to be used is all that is required. However, if the primary antibody needs to be labeled and it is not manufactured commercially, then a custom labeling procedure will have to be done. 

Price, M.R., Sekowski, M., Hooi, D.S.W., Durrant, L.G., Hudecz, F., and Tendler, S.J.B. (1993) Measurement of antibody binding to antigenic peptides conjugated in situ to albumin-coated microti-tre plates./. Immunol. Meth. 159, 277-281. 

IHC techniques provide important tools for the localization of specific antigens within individual cells. In CL IHC the probes used are highly specific antibodies that bind to antigens such as proteins, enzymes, and viral or bacterial products. The bound specific antibody is revealed indirectly by species-specific or class-specific secondary antibodies conjugated to CL enzymes. 

Figure 1.11. Schematic representation of an IgG molecule. The heavy chains comprise three constant regions (Cri-C ) the molecular sites involved in binding to antigen, complement or to Fc receptors are indicated.

B cells are produced by the bone marrow. In response to activation of CD4+ T helper cells (see below), B cells proliferate and produce antibodies. (The term CD stands for cluster of differentiation. They are proteins coating cell surfaces. Altogether, there are more than 160 different types of CDs.) The antibodies produced by B cells circulate in the bloodstream and bind to antigens. Once bound, other cells are in turn activated to destroy the antigens. 

Compare and contrast the different types of antibody immunoglobulins. Provide a detailed description of the structure of the IgG antibody with particular reference to how it binds to antigens. 

They bind to antigens on the surface of pathogens and thereby prevent them from interacting with body cells (neutralization see p. 404, for example). 

As well as their function in binding to antigen, immunoglobulins have other roles within the immune system that necessitate interactions with other proteins such as those of the complement and phagocytic systems. In techniques such as immunofluorescence or in in vivo applications, these interactions can be problematic but can be solved by the use of selective proteolysis to remove parts of the molecule. The polypeptide chains making up the IgG molecule... 

Type II, or cytotoxic immune, responses can be complement-independent or complement-dependent in nature. In the former case, IgG antibodies bind to antigens attached to the surface of normal cells (e.g., erythrocytes, platelets, etc.). Cytotoxic cells (macrophages, neutrophils, and eosinophils) then attach to the crystallizable fragment (Fc) portion of the antigen, release cytotoxic granules, and lyse the cell. 

Hawkins RE, Russell SJ, Baier M, Winter G, The contribution of contact and noncontact residues of antibody in the affinity of binding to antigen. The interaction of mutant D1.3 antibodies with lysozyme, J. Mol. Biol., 234 958-964, 1993. 

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