Immunoprecipitation (IP) and coimmunoprecipitation (co-IP) are key techniques 
for studying protein-protein interactions. These methods utilize immobilized 
Protein A or Protein G to isolate antibody-bound target antigens. The main 
disadvantage of traditional IP and co-IP is that the conditions used to elute 
the precipitated antigen also release the antibody thus contaminating the 
antigen and destroying the antibody support. To overcome these problems, we 
describe two methods to generate a reusable antibody support by cross-linking 
the antibody to immobilized Protein A or Protein G, or by coupling it directly 
to the resin (see Scheme 1). Antibody cross-linking can be done in 1 h while 
antibody coupling requires 4 h. IP or co-IP is accomplished by incubating the 
antibody resin with the protein sample. Washes and elutions are carried out in a 
spin column to reduce resin loss and decrease assay time. Target proteins are 
eluted with 0.1 M glycine (pH 2.8) and the resin-bound antibody is 
re-equilibrated in phosphate-buffered saline (PBS) for reuse. Our studies have 
demonstrated that the immobilization efficiency for the antibody coupling method 
was similar for several species of antibody. Furthermore, we illustrate that 
using both methods of antibody immobilization yield IP and co-IP results similar 
to traditional protocols but eliminate the antibody heavy and light chain 
contamination.