Antisera to human IgE can also recognize IgA and IgM molecules as produced by selected B lymphoblastoid cell lines.

A series of polyclonal and monoclonal anti-human IgE sera reacted with a panel of 11 selected IgA and IgM producing B lymphoblastoid cell lines (BLCLs) in cytoplasmic fluorescence, ELISA and immunoprecipitation assays. The reactions were discordant between the BLCLs and the individual antisera. The panel of 11 BLCLs was selected from over 500 BLCLs by an ELISA spot assay using a polyclonal anti-human IgE serum. The BLCLs produced exclusively IgM or IgA, both with either kappa or lambda light chains as shown by immunoprecipitation/PAGE and mRNA analyses. The data indicate that IgE antisera may recognize IgE-like epitopes on the variable parts of some IgM or IgA molecules. These reactivities of IgE antisera may lead to false positive results of serum IgE determinations. Selected BLCLs are useful targets for exposing such reactivities in IgE antisera.