Target Signal Masked by IgG Heavy/Light Chains (Immunoprecipitation (CST Guide))

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Western blot after IP shows strong bands at ~25 kDa and ~50 kDa obscuring target protein. Target protein migrating near these molecular weights cannot be detected due to overwhelming IgG signal. Common causes: 1) Denatured IgG light chain (25 kDa) and heavy chain (50 kDa) from IP antibody detected by western blot secondary antibody 2) Same host species antibody used for both IP and western blot detection, causing secondary to recognize IP antibody chains 3) High concentration of IP antibody IgG chains overwhelms target protein signal at similar molecular weight Solutions: 1) Use antibodies from different species for IP versus western blot (e.g., rabbit for IP, mouse for WB, or vice versa) with species-specific secondaries (Anti-rabbit IgG HRP #7074, Anti-mouse IgG HRP #7076) 2) Use biotinylated primary antibody from same species for western blot, detect with Streptavidin-HRP #3999 (no IgG cross-reactivity) 3) If target does not migrate near 25 kDa, use light chain-specific secondary: Mouse Anti-Rabbit IgG (Light-Chain Specific) (D4W3E) mAb HRP #93702 or Rabbit Anti-Mouse IgG (Light Chain Specific) (D3V2A) mAb HRP #58802 4) Replace western blot secondary with Protein A (HRP Conjugate) #12291, which preferentially binds native IgG (note: may cross-react with denatured IgG at high concentrations) 5) Use conformation-specific secondary antibody: Mouse Anti-Rabbit IgG (Conformation Specific) (L27A9) mAb #5127, preferentially binding native IgG (note: may cross-react with denatured IgG at high concentrations)