Secondary antibody recognizes denatured/reduced primary antibody released during the IP procedure or endogenous IgGs
Using secondary antibodies, recognizing the heavy and light-chain of the primary antibody for WB detection of IP samples will always result in two bands (the heavy-chain at 50kDa and the light-chain at 25kDa).
To avoid interference by the antibody chains we recommend using secondary antibodies, such as VeriBlot for IP, that specifically recognize native (non-reduced) primary antibodies.