This polyclonal antibody reacts with whole molecule rat IgG (heavy and light chains) and may also react with the light chains of other rat immunoglobulins. The antibody has been reported to be reactive in ELISA with rat IgG, IgM, and IgA. In addition, some cross-reactivity with mouse IgG, some hamster Ig and minimal cross-reactivity with human Ig has been reported. Investigators experiencing cross-reactivity with rat IgM may wish to consider using the following alternatives: Biotin Mouse Anti-Rat IgM (Cat. No. 553886) or Biotin Mouse Anti-Rat Ig, κ light chain (Cat. No. 553871). Minimal cross-reaction to mouse, human, bovine, horse and rabbit non-immunoglobulin serum proteins are expected. For immunohistochemical staining (IHC) of acetone-fixed frozen and paraffin-embedded sections, Biotin Goat Anti-Rat Ig (Cat. No. 559286) is recommended. When using rat IgG2b primary antibodies, Biotin Mouse Anti-Rat IgG2b (Cat. No. 550327) is also available as an alternate. When using rat IgM primary antibodies, Mouse Anti-Rat/Hamster Ig κ light chain (Cat. No. 550336) or Mouse Anti-Rat IgM (Cat. No. 550330) are also available alternatives.