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Sci Rep. 2019 May 14;9(1):7363. doi: 10.1038/s41598-019-40731-2.

Reduced FcRn-mediated transcytosis of IgG2 due to a missing Glycine in its lower hinge.

Author information

1
Sanquin Research, Department of Experimental Immunohematology, Amsterdam, The Netherlands, and Landsteiner Laboratory, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands, Plesmanlaan 125, Amsterdam, 1066 CX, The Netherlands.
2
HALIX B.V., J.H. Oortweg 15/17, 2333 CH, Leiden, The Netherlands.
3
Department of Pathology, Division of Immunology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK.
4
Department of Haematology, University of Cambridge, Cambridge, UK.
5
LifeArc, Open Innovation Campus, Stevenage, SG1 2FX, UK.
6
Sanquin Reagents, Amsterdam, Netherlands.
7
Clark Antibodies Ltd, 10 Wellington Street, Cambridge, CB1 1HW, UK.
8
NHS Blood and Transplant, Long Road, Cambridge, CB2 2PT, UK.
9
Sanquin Research, Department of Experimental Immunohematology, Amsterdam, The Netherlands, and Landsteiner Laboratory, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands, Plesmanlaan 125, Amsterdam, 1066 CX, The Netherlands. G.Vidarsson@sanquin.nl.

Abstract

Neonatal Fc-receptor (FcRn), the major histocompatibility complex (MHC) class I-like Fc-receptor, transports immunoglobuline G (IgG) across cell layers, extending IgG half-life in circulation and providing newborns with humoral immunity. IgG1 and IgG2 have similar half-lives, yet IgG2 displays lower foetal than maternal concentration at term, despite all known FcRn binding residues being preserved between IgG1 and IgG2. We investigated FcRn mediated transcytosis of VH-matched IgG1 and IgG2 and mutated variants thereof lacking Fc-gamma receptor (FcγR) binding in human cells expressing FcRn. We observed that FcγR binding was not required for transport and that FcRn transported less IgG2 than IgG1. Transport of IgG1 with a shortened lower hinge (ΔGly236, absent in germline IgG2), was reduced to levels equivalent to IgG2. Conversely, transport of IgG2 + Gly236 was increased to IgG1 levels. Gly236 is not a contact residue between IgG and FcRn, suggesting that its absence leads to an altered conformation of IgG, possibly due to a less flexible Fab, positioned closer to the Fc portion. This may sterically hinder FcRn binding and transport. We conclude that the lack of Gly236 is sufficient to explain the reduced FcRn-mediated IgG2 transcytosis and accounts for the low maternal/fetal IgG2 ratio at term.

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