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Western Cross-Blotting 1025<br />

149<br />

Detection of Serological Cross-Reactions<br />

by Western Cross-Blotting<br />

Peter Hammerl, Arnulf Hartl, Johannes Freund, and Josef Thalhamer<br />

1. Introduction<br />

Antisera are frequently used tools for the characterization of proteins and peptides<br />

because they provide unique information about the structural features of antigens. <strong>Protein</strong>s<br />

that share structural similarities can be identified by serological cross-reactions.<br />

The Western blotting technique combines two steps that are characteristic for<br />

immunoaffinity chromatography (1). One is the preparation of monospecific antibodies<br />

against a particular antigen and the second is the testing of their reactivity with the<br />

same or different antigens from any source of antigenic material.<br />

As a rule, such experiments turn out to be elaborate and time-consuming procedures,<br />

consisting of many different steps; particularly because either a purified antigen<br />

or a monospecific antibody are basic requirements. In many cases, monospecific antibodies<br />

need to be purified from polyspecific antisera by immunoaffinity chromatography.<br />

However, only small amounts of monospecific antibody are required for analytical<br />

purposes. In such a case it may be sufficient to elute antibodies from selected bands off<br />

a Western blot. One protocol, for example, has been published by Beall and Mitchell (2).<br />

In contrast to experimental setups for the immunochemical analysis of one particular<br />

antigen, the method described in this chapter is especially designed for single-step<br />

analysis of cross-reactivities of multiple antigens, within the same or between different<br />

protein mixtures. The principle is to test antibodies that have bound to particular antigen<br />

bands of a Western blot against all antigen bands on a second blot. This is done by<br />

electrotransfer of antibodies from one Western blot to a second one, taking advantage<br />

of the dissociative effect of chaotropic ions on antigen–antibody complexes.<br />

The strategy can be dissected into the following steps:<br />

1. Two antigen mixtures are separated by sodium dodecyl sulfate-polyacrylamide gel<br />

electrophoresis (SDS-PAGE), each mixture on a separate gel. The samples are loaded<br />

onto the entire width of the gels. After electrophoresis, the proteins are blotted onto<br />

nitrocellulose (NC) paper.<br />

2. One of the two blots (referred to as the “donor” blot in this text) is incubated with a<br />

polyspecific antiserum and then placed onto the second blot (“receptor” blot), upside<br />

From: The <strong>Protein</strong> <strong>Protocols</strong> Handbook, 2nd Edition<br />

Edited by: J. M. Walker © Humana Press Inc., Totowa, NJ<br />

1025

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