PURIFICATION AND CHARACTERIZATION OF CHIMERIC HUMAN IGA1 AND IGA2 EXPRESSED IN COS AND CHINESE-HAMSTER OVARY CELLS

Ag-specific chimeric human IgA molecules, of the two human subclasses, IgA1 and IgA2, have been expressed in two mammalian cell systems. Ana lysis of the secreted IgA molecules, purified in milligram quantities from stable Chinese hamster ovary transfectants by Ag affinity chromat ography, has allowed a direct comparison of the biologic properties of the two subclasses. HPLC gel filtration analysis revealed that in bot h subclasses, the IgA molecules associate predominantly into dimers. T he monomer units are presumed to interact noncovalently, inasmuch as n o dimers are evident when the antibodies are subjected to SDS-PAGE. Th e recombinant antibodies are glycosylated, inasmuch as a lectin blotti ng procedure revealed that the H chains of both subclasses are recogni zed by Con A. When subjected to digestion by preparations of IgA1-spec ific proteases secreted by two pathogenic streptococcal strains, Strep tococcus sanguis and Streptococcus oralis, the recombinant IgA molecul es behave just as their natural equivalents. Thus, only the chimeric I gA1 molecule is cleaved, with the IgA2 remaining intact. In terms of i nteraction with natural effector molecules, both recombinant IgA isoty pes were shown to interact with Fcalpha receptors on calcitriol-stimul ated HL-60 cells with similar affinity, but neither antibody was found to interact with human C1q. The expression system described readily p ermits manipulation of the human IgA genes, which should lead to a ful ler molecular understanding of how this important antibody mediates it s function.