[21] The two-cross immunodiffusion technique for determining diffusion coefficients and precipitating titers of antigen and antibody

Publisher Summary This chapter discusses the two-cross immunodiffusion technique for determining the diffusion coefficients and precipitating titers of antigen and antibody. The two-cross immunodiffusion technique is essentially a two-dimensional double immunodiffusion procedure. The diffusion proceeds simultaneously from two crosses, each consisting of four troughs cut at a right angle in a gel plate. The troughs of each cross are filled in alternate order with antigen solution and antibody solution. The concentrations of the diffusing components are adjusted to obtain a narrow and sharp precipitation band in the gel plate. The two-cross immunodiffusion technique is restricted to the antigen and antibody concentrations that give visible precipitin bands. The consistency of the results over time obtained for precipitating titers, critical precipitating concentrations, and diffusion coefficients for the immunoprecipitating system human IgG in serum-rabbit antibody preparation is discussed in the chapter. It is found that the antigen-to-antibody ratio in the precipitate at the equivalency for the system IgG-anti-IgG is constant from pH 5 up to pH 7, and then increases slightly.