Antigens bivalent

The advantage of this system is linked with the specificity of the mAb in possibly capturing only the targeted antigen. Bivalent mAbs usually capture well, but have to be tested individually for required performance. 

Antibody molecules are bivalent whilst antigens can be multivalent. The resultant combination may result in either small, soluble complexes, or large insoluble aggre tes, depending on the nature of the two molecules in the system. The following are examples of the reactions that can occur. 

The fluidity of lipid bilayers permits dynamic interactions among membrane proteins. For example, the interactions of a neurotransmitter or hormone with its receptor can dissociate a transducer protein, which in turn will diffuse to interact with other effector proteins (Ch. 19). A given effector protein, such as adenylyl cyclase, may respond differently to different receptors because of mediation by different transducers. These dynamic interactions require rapid protein diffusion within the plane of the membrane bilayer. Receptor occupation can initiate extensive redistribution of membrane proteins, as exemplified by the clustering of membrane antigens consequent to binding bivalent antibodies [8]. In contrast to these examples of lateral mobility, the surface distribution of integral membrane proteins can be fixed by interactions with other proteins. Membranes may also be partitioned into local spatial domains consisting of networks... 

The polyvalency of IgM causes it to bind more firmly to an antigen than either a univalent or bivalent antibody. In this respect, a single molecule of IgM can cause lysis of a cell. Furthermore, the joining chain (J) has been detected in polymeric IgM and IgA, but not in the other immunoglobulins. About 10% of the IgM in external secretions has the secretory component attached. One wonders whether these characteristics of the IglNI are responsible for its take-over role in the gut, when there is a defective synthesis of IgA as in celiac or in Crohn s disease or in ulcerative colitis. 

Calculation of binding capacity if IgG is the antibody used for immobilization the molar ratio between the IgG and the antigen (analyte) is 1 2 because IgG is bivalent. Thus, the theoretical binding capacity of the column is as follows ... 

Each IgG antibody molecule consists of four polypeptide chains (two identical light chains and two identical heavy chains joined by disulfide bonds) and has two antigen-binding sites (i.e. is bivalent). 

Above we described only rather simple cases, for which the stoichiometry of interaction is 1 1 or n l, and cooperativity effect is absent. In strict terms, neither of the mentioned linear transformations is suited for more complex systems such as, e.g., bivalent antibodies and multivalent antigens. Only rough estimation of the total affinity is possible. Separate determinations of the affinity of all interactions occurring in a studied multivalent system (see, e.g., Ref. 7)... 

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