 However, when compared with natural cells there does appear to be a difference between IgM and IgG antibody reactivities when the functional group (F) is a monomeric peptide antigen.IgM antibodies appear to react poorly with kodecytes made with FSL peptides.Furthermore, FSL constructs may have a restricted antigen/epitope and may not react with a monoclonal antibody unless the FSL construct and monoclonal antibody are complementary.