EFFECT OF ALTERED C(H)2-ASSOCIATED CARBOHYDRATE STRUCTURE ON THE FUNCTIONAL-PROPERTIES AND IN-VIVO FATE OF CHIMERIC MOUSE-HUMAN IMMUNOGLOBULIN G1

Immunoglobulin G (IgG) molecules are glycosylated in C(H)2 at Asn297; the N-linked carbohydrates attached there have been shown to contribut e to antibody (Ab) stability and various effector functions. The carbo hydrate attached to the IgG constant region is a complex biantennary s tructure. Alterations in the structure of oligosaccharide have been as sociated with human diseases such as rheumatoid arthritis and osteoart hritis. To study the effects of altered carbohydrate structure on Ab e ffector function, we have used gene transfection techniques to produce mouse-human chimeric IgG1 Abs in the Chinese hamster ovary (CHO) cell line Lec 1, which is incapable of processing the high-mannose interme diate through the terminal glycosylation steps. We also produced IgG1 Abs in Pro-5, the wild-type CHO cell line that is the parent of Lec 1. The Pro-5-produced Ab (IgG1-Pro-5) was similar to IgG1-My 1, a myelom a-produced IgG1 Ab of the same specificity, in its biologic properties such as serum half-life, ability to effect complement-mediated cytoly sis, and affinity for Fc gamma RI. Although the Lec 1-produced Ab, IgG 1-Lec 1, was properly assembled and retained antigen specificity, it w as incapable of complement-mediated hemolysis and was substantially de ficient in complement consumption, Clq binding, and C1 activation. IgG 1-Lec 1 also showed reduced but significant affinity for Fc gamma R1 r eceptors. The in vivo half-life of IgG1-Lec 1 was shorter than that of either the myeloma- or Pro-5-produced counterpart, with more being cl eared during the cr-phase and with more rapid clearance during the bet a-phase. Clearance of IgG1-Lec 1 could be inhibited by the administrat ion of yeast-derived mannan. Thus the uptake of IgG1-Lec 1 appears to be accelerated by the presence of terminally mannosylated oligosacchar ide. Therefore, certain Ab functions as well as the in vivo fate of th e protein are dramatically affected by altered carbohydrate structure. Expression of Igs in cell lines with defined glycosylation mutations is shown to be a useful technique for investigating the contribution o f carbohydrate structure to Ab function.