See Ivell et al (20) for more details. Immunohistochemistry of tissues from gene-deleted animals An ideal control, where feasible, is to make use of tissues in which the target gene product of interest has been genetically deleted. powerful tools in modern biological science. They combine extremely high precision of identification at the protein level, with high sensitivity, and also localization at a cellular or even a subcellular scale. Although the technique of immunocytochemistry has been around for some 50 years (1), the methodology itself is still relatively crude, and our understanding of what factors influence specificity and sensitivity is usually often rudimentary. In the postgenomic era of the Internet we are inundated by information from companies (R)-Baclofen offering large numbers of antibodies, mostly against peptides or (R)-Baclofen recombinant proteins, all of which postulate very high specificity combined with rigorous controls. But how much of this should we believe, and what are the minimal controls that still need to be carried out to ensure adequate scientific rigor in our experiments? Referees and journal editors are becoming alarmed by the often superficial way in which antibody specificity is usually dealt with (2,C4). This guide briefly discusses how antibodies are produced, how they function in the context of immunohistochemistry, and what controls and documentation are essential if a result is to be believed. Unfortunately, the scientific literature is usually pervaded by examples of erroneous results using antibodies, particularly in immunohistochemistry. Here we hope to alert the investigator and potential referees to the possible pitfalls that can be encountered. What Are Antibodies? What Types Are There? How Are They Generated? This article cannot hope to summarize the vast amount of very detailed literature concerning antibodies, their generation, and their functionality. There are numerous excellent reviews and books covering these topics (eg, Refs. 5,C9). Here we intend to introduce only sufficient knowledge of antibodies to explain the issues that contribute to the way they work in our experimental systems and, consequently, also their limitations and potential artifacts. In general, antibodies are produced (R)-Baclofen by B cells (or plasma cells) within the body as part of the humoral response to contamination. Antibodies circulate in the blood or in peritoneal fluid, or may be attached to the surface of lymphocytes, and serve to interact specifically with foreign antigens, causing these to be ingested by phagocytosis. Antibodies are of several types, the most common being IgG, which possesses 2 larger heavy chains, each linked to shorter chains by disulfide bridges (Physique 1). The ends of the chains form a hypervariable paratope (Physique 1), which can specifically recognize a small 3-dimensional differentially charged surface (the immunological epitope) of its cognate immunogen (the protein used for immunization), which we refer to as the antigen (meaning antibody-generating molecule). Upon infection or immunization, specific IgG molecules, and the cells producing them, are (R)-Baclofen clonally selected, and variability can be amplified by recombination and site-specific mutation within these cells. Immunization of a living mammal with a large immunogen gives rise to so-called polyclonal antisera, because many different IgGs are generated, each recognizing a different 3-dimensional epitope within the same immunizing protein. For comprehensive details of immunization procedures, see Harlow and Lane (6, 7). Antisera are the serum or sometimes plasma fractions from the blood of immunized animals. The IgG fraction within the antiserum may be further purified crudely, for example, using the IgG-specific binding properties of Protein A or Protein G, or by differential ammonium sulfate precipitation. Alternatively, an antiserum can be purified quite specifically by using (R)-Baclofen affinity chromatography binding to the original immunizing antigen. Such affinity-purified antisera, although highly enriched in the specific IgG, may have lost concentration (titer) because the highest affinity antibodies do not elute well from the columns, and/or may be structurally damaged by the exposure to the very acidic pH needed to elute KRT13 antibody the antibodies from the affinity column. In general, species are chosen for immunization, which are evolutionarily distant from either the species of the immunizing antigen, and/or the species in which the antibodies are to be applied. Most commonly, polyclonal antibodies are raised in rabbits, guinea pigs, donkeys, goats, or sheep, although other species (eg, rats or chicken) may also be used. Open in a separate window Physique 1. Diagrammatic representation of an IgG molecule to indicate terms used in the text. Fab fragments are those generated by papain cleavage and comprise only a single antigen-combining site, whereas F(ab)2 fragments are generated by pepsin cleavage and have 2 antigen-combining sites. Monoclonal antibodies are created in much the same way as polyclonal antibodies by the immunization of living mice (or sometimes rats). However,.
