Hybrid immunoglobulin isotypes of identical specificity produced by genetic recombination in Escherichia coli and expression in lymphoid cells

We have produced a series of hybrid IgG₁-IgG_2a mouse immunoglobulins with identical light chains (L) and variable regions to facilitate the identification of structural features associated with functional differnces between immunoglobulin isotypes. Hybrid heavy chain (H) constant region gene segments were generated by genetic recombination in Escherichia coli between plasmids carrying mouse γ¹ and γ^2a gene segments. Crossovers occured through out these segments although the frequency was highest in regions of high nucleotide sequence homology. Eleven variant immunoglobulins produced by transfected hybridoma cell lines are assembled into H₂L₂ tetramers and properly glycosylated. In addition, all 11 immunoglbulins have identical antigen combining sites specific for the fluorescent hapten ε-dansyll-L-lysine. Protein A binding was used as probe of the structural integrity of the Fc portion of the variant antibodies. Differeneces in protein A binding between IgG₁ and IgG_2a appear to be due to amino acid differances at postions 252 (Thr→Met) and 254 (Thr→Ser) of the heavy chain (EU numbering).