Polyclonal and Monoclonal Antibodies
The breadth of repertoire yet beautiful specificity of the antibody response is the key to its physiological efficacy in vivo; it also underpins the attractiveness of antibodies as laboratory and clinical reagents. One aspect of the body’s reaction to inv
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2 Polyclonal and Monoclonal Antibodies Mary A. Ritter 1. Introduction The breadth of repertoire yet beautiful specificity of the antibody response is the key to its physiological efficacy in vivo; it also underpins the attractiveness of antibodies as laboratory and clinical reagents. One aspect of the body’s reaction to invasion by a microorganism is the activation and clonal expansion of antigen-reactive B lymphocytes. Once these have matured into plasma cells, each clone of cells will secrete its own unique specificity of antibody—thus, the invading pathogen will be met by a barrage of antibody molecules capable of binding to many different sites on its surface. Such a polyclonal response, whose range of specificities and affinities can shift with time, is ideal for combatting infection, and indeed for certain laboratory applications (such as secondary reagents for immunoassay); however, in many experimental and clinical situations the ability to have an unlimited supply of a single antibody that is clearly defined and of reproducible specificity and affinity is of greater value. To produce such a reagent it is necessary to isolate and culture a single clone of B lymphocytes secreting antibody of the appropriate characteristics—that is, to produce a monoclonal antibody (mAb). 2. Generation of an Immune Response 2.1. Selection of Animal for Immunization The generation of an immune response to the antigen of interest is a necessary prerequisite to the production of both polyclonal and monoclonal antibodies; the major difference between the two systems lies mainly in the size of the animal to be immunized. Since polyclonal antibodies are collected from the serum of the immunized individual it is advisable to use as large an animal as From: Methods in Molecular Medicine, Vol. 40: Diagnostic and Therapeutic Antibodies Edited by: A. J. T. George and C. E. Urch © Humana Press Inc., Totowa, NJ
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possible; for commercial reagents rabbit, goat, and sheep are the usual choices, although pig, donkey, horse, and kangaroo antibodies are also available. For a phylogenetically more distant view of a mammalian immunogen, the chicken can be very useful. Two further factors affect the choice of animal. First, the greater the genetic disparity between donor antigen and recipient to be immunized, the greater the number of distinct epitopes to which the immune response can be directed. Thus, unless the target antigen is a defined alloantigen, the recipient should be as phylogenetically unrelated to the donor as possible. For polyclonal antibodies this is not a problem since the choice of recipient is a wide one. However, for mAbs, for which mouse, rat, and hamster are the best source of immune cells (see Subheading 4.2.), this can cause a problem for those working with rodent antigens. Second, it is better to use female recipients since they, in general, mount a more effective immune response than their male counterparts—a characteristic that has as its downside an increased incidence of autoimmune disease. Additio
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