I am trying to screen human B cell culture supernatants for autoreactivity on Hep-2 slides (IFA). The supernatants contain both IgG (~10μg/mL) and IgM (~60μg/mL) antibodies. There are several commercially available kits for IgG reactivity (eg. Inova Diagnostics), but nothing for IgM. Has anyone tried to screen IgM antibodies on Hep-2 cells? What is the secondary antibody used? Any tips? I have tried a couple of polyclonal anti-IgM antibodies (rabbit and goat) but I am getting too much background staining...I also tried a goat polyclonal antibody against light chains that reacts with both IgG and IgM that stains nicely but obviously cannot distinguish between IgM and IgG...