Mouse immunoglobulin allotypes: multiple differences between the nucleic acid sequences of the IgEa and IgEb alleles

To clarify the allotypic difference of the IgE antibody molecule, we determined the complete nucleotide sequence of the genes encoding the constant portion of mouse IgE of a (BALB/c) as well as b (B10.A) allotypes. A comparison of the sequences revealed that there were 12 single-base changes: 2 single-base changes in CH1 and CH2, 3 in CH3, and 7 in CH4. Five of them were silent changes, but seven resulted in amino acid substitutions. Although the silent changes are scattered through CH1 to CH4, the nonsilent substitutions were found only in CH3 (two substitutions) and CH4 (five). The allotypic determinant(s) that conventional antisera detect most likely reflects an amino acid difference(s) in CH3 and/or CH4.