Comparative analysis of IgM sub-variants in salmonid fish and identification of a residue in μ3 which is essential for MAb4C10 reactivity

► Salmon IgM-B holds a higher degree of inter-chain disulfide bonding than IgM-A. ► A proline residue in salmon μA3 is essential for MAb4C10 binding. ► Two distinct μ genes are present in the genome of arctic char. ► Hybrids of char and salmon express four μ sub-variants.