Introduction to Immunoprecipitation (IP)

IP is a technique used to enrich or purify a specific protein from a complex mixture using an antibody.

During IP, an antibody (monoclonal or polyclonal) is allowed to form an immune complex with the antigen it recognizes, typically a protein present in a suspension (e.g. cell lysate). The immune complex is then captured on a solid support (e.g.agarose or sepharose) carrying immobilized Protein A or Protein G. After washing away any proteins not bound by the immobilized Protein A or G, the components of the immune complex(antibody and antigen) are eluted and analyzed by SDS-PAGE, often followed by Western blot analysis (WB) to visualize the protein of interest. 

Comparision between polyclonal antibodies and monoclonal antbibodies

Polyclonal antibodies Monoclonal antibodies
Inexpensive to produce Expensive to produce
Skills required are low Training is required for the technology used
Time scale is short Time scale is long for hybridomas
Produces large amounts of non-specific antibodies Can produce large amounts of specific antibodies
Recognizes multiple epitopes on any one antigen Recognizes only one epitope on an antigen
Can have batch-to-batch variability Once a hybridoma is made, it is a constant and renewable source
- No or low batch-to-batch variability