Evaluation of blocking agents in protein A-gold immunocytochemistry
Various blocking agent solutions are used in protein A-gold immunocytochemistry to prevent or reduce nonspecific attachment of antibodies and/or protein A-gold particles to tissue sections. In our study of intracellular antigens present at low levels, the inadequacy of some commonly used blocking solutions became evident. We, therefore, compared several blocking solutions by exposing L929 cell cultures, at 4 °C, to a hapten-labeled lectin (dinitro-phenol-labeled wheat germ agglutinin, DNP-WGA) that binds specifically to the plasma membrane. We then used the protein A-gold method to locate the bound DNP-WGA. Since endocytosis had been prevented, gold particles not associated with the plasma membrane were regarded as nonspecific.The cells were incubated with DNP-WGA for 2 h at 4 °C, and were then fixed with 2% glutaraldehyde and 2% paraformaldehyde in 0.1 M cacodylate buffer, pH 7.2. Some samples were also postfixed with osmium tetroxide.