Differential clearance of glycoforms of IgG in normal and autoimmune-prone mice

Abstract

SUMMARYIn order to understand better the origins of the elevated levels of the glycoform of IgG that lacks galactose on both arms of the oligosaccharide chain (G0%) located in the Fc, which occurs in man and mouse with age, and in particular in autoimmune disease, we investigated the clearance of two glycosylated forms of IgG2a and IgG1 in normal (BALB/c) and autoimmune-prone (MRL/lpr, MRL/, and non-obese diabetic (NOD)) mice. To investigate the possibility of different rates of catabolism, enzymatically generated glycoforms of monomeric IgG1 and IgG2a (fully glycosylated or G0%), were iodinated and injected into the tail vein of the mice. We found that the G0% IgG2a remained in circulation significantly longer than the fully glycosylated variants, in all of the mouse strains tested. In contrast, the two forms of IgG1 had similar kinetics in all the autoimmune-prone mice, whereas in BALB/c, there was a longer half-life (t 1/2 ) for G0% IgG1. These data suggest that there may be differences in the ability of the IgG glycoforms to bind to the Fc°receptors, in particular Fc°RI. The clearance rates were found to vary among the strains studied, with MRL/lpr having the fastest catabolic rates for all glycoforms and IgG subclasses tested. This appeared to be due to the presence of circulating IgG and IgM rheumatoid factors (RF). There were significantly increased frequencies and titres for both IgM and IgG RF in MRL/lpr mice compared with the other strains. In contrast, interferon-gamma, known to induce the Fc°RI, was found to be similar in the sera, in all of the strains of mice examined. These results suggest that RF probably play an important biological function in the MRL/lpr mice and aid in the clearance of circulating IgG. Our study shows that the state of glycosylation of IgG affects the t 1/2 in vivo, and that by removing the terminal sugars (sialic acid and galactose), the antibody (IgG2a) will remain in circulation significantly longer. These observations may thus provide a partial explanation for the increase in relative percentage of this glycoform that occurs with age.

A novel in vitro assay to predict neonatal Fc receptor-mediated human IgG half-life

“…Early reports were conflicted regarding effects of glycosylation on antibody half-life, 18,[72][73][74][75] but our results support the most recent reports suggesting glycosylation does not affect FcRn-mediated PK. [66][67][68][69] In our study, this was confirmed by removing all N-glycosylation (only the natural germline Fc glycosylation site exists in the antibodies tested) and the in vitro FcRn binding measurement was used to compare the aglycosylated mAb to the naturally occurring glycosylated form produced in CHO cells.…”

A prominent lack of IgG1-Fc fucosylation of platelet alloantibodies in pregnancy

“…A high degree of galactosylation has been found to negatively affect IgG half-life in mice, 40 suggesting that galactosylation may also influence the transport of IgG from mother to child because both half-life and transport of IgG are mainly mediated by the neonatal Fc receptor FcRn. 41 However, no such skewing for IgG transport across the human placenta was found in our previous study, 42 in accordance with the fact that the Fc glycans are not involved in binding to FcRn.…”

Improved tumor targeting of anti–epidermal growth factor receptor Nanobodies through albumin binding: taking advantage of modular Nanobody technology

“…Several strategies have been described in literature to reduce blood clearance of targeting molecules. Most of these strategies focus on the enlargement of the targeting molecule above the critical size for renal clearance (60-70 kDa) by fusion to other proteins like albumin (30) and the Fc portion of an IgG (31) or by glycosylation (32) or pegylation (33). The use of bispecific antibodies as described herein, aiming a noncovalent association with albumin as a means to improve biodistribution and tumor deposition, was pioneered by Dennis et al from the Genentech labs (17).…”