Isotyping and quantitation of murine IgG2a antibodies are widely performed with commercial monoclonal and polyclonal antisera raised against BALB/c IgG2a myeloma proteins. Recently it became evident that inbred mouse strains with the Igh1-b allele do not have the gene for IgG2a and instead express the IgG2c isotype. We show that commercial anti-IgG2a sera cross-react inadequately against IgG2c in immunoblot and ELISA and hence, are not suitable to detect and measure this subclass in mouse strains such as C57BL/6, C57BL/10 and NOD. We have used DNA immunization to generate polyclonal anti-IgG2c serum and demonstrated that it is essential to use IgG2c-specific antiserum to quantify accurately isotypic responses in mouse strains with the Igh1-b allele.
