TY - JOUR
T1 - IgG4 autoantibodies against muscle-specific kinase undergo Fab-arm exchange in myasthenia gravis patients
AU - Koneczny, Inga
AU - Stevens, Jo A. A.
AU - De Rosa, Anna
AU - Huda, Saif
AU - Huijbers, Maartje G.
AU - Saxena, Abhishek
AU - Maestri, Michelangelo
AU - Lazaridis, Konstantinos
AU - Zisimopoulou, Paraskevi
AU - Tzartos, Socrates
AU - Verschuuren, Jan
AU - van der Maarel, Silvere M.
AU - van Damme, Philip
AU - De Baets, Marc H.
AU - Molenaar, Peter C.
AU - Vincent, Angela
AU - Ricciardi, Roberta
AU - Martinez-Martinez, Pilar
AU - Losen, Mario
PY - 2017/2
Y1 - 2017/2
N2 - Autoimmunity mediated by IgG4 subclass autoantibodies is an expanding field of research. Due to their structural characteristics a key feature of IgG4 antibodies is the ability to exchange Fab-arms with other, unrelated, IgG4 molecules, making the IgG4 molecule potentially monovalent for the specific antigen. However, whether those disease-associated antigen-specific IgG4 are mono- or divalent for their antigens is unknown. Myasthenia gravis (MG) with antibodies to muscle specific kinase (MuSK-MG) is a well recognized disease in which the predominant pathogenic IgG4 antibody binds to extracellular epitopes on MuSK at the neuromuscular junction; this inhibits a pathway that clusters the acetylcholine (neurotransmitter) receptors and leads to failure of neuromuscular transmission. In vitro Fab-arm exchange-inducing conditions were applied to MuSK antibodies in sera, purified IgG4 and IgG1-3 sub-fractions. Solid-phase cross-linking assays were established to determine the extent of pre-existing and inducible Fab-arm exchange. Functional effects of the resulting populations of IgG4 antibodies were determined by measuring inhibition of agrin-induced AChR clustering in C2C12 cells. To confirm the results, kappa/kappa, lambda/lambda and hybrid kappa/lambda IgG4s were isolated and tested for MuSK antibodies. At least fifty percent of patients had IgG4, but not IgG1-3, MuSK antibodies that could undergo Fab-arm exchange in vitro under reducing conditions. Also MuSK antibodies were found in vivo that were divalent (monospecific for MuSK). Fab-arm exchange with normal human IgG4 did not prevent the inhibitory effect of serum derived MuSK antibodies on AChR clustering in C2C12 mouse myotubes. The results suggest that a considerable proportion of MuSK IgG4 could already be Fab-arm exchanged in vivo. This was confirmed by isolating endogenous IgG4 MuSK antibodies containing both kappa and lambda light chains, i.e. hybrid IgG4 molecules. These new findings demonstrate that Fab-arm exchanged antibodies are pathogenic. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.
AB - Autoimmunity mediated by IgG4 subclass autoantibodies is an expanding field of research. Due to their structural characteristics a key feature of IgG4 antibodies is the ability to exchange Fab-arms with other, unrelated, IgG4 molecules, making the IgG4 molecule potentially monovalent for the specific antigen. However, whether those disease-associated antigen-specific IgG4 are mono- or divalent for their antigens is unknown. Myasthenia gravis (MG) with antibodies to muscle specific kinase (MuSK-MG) is a well recognized disease in which the predominant pathogenic IgG4 antibody binds to extracellular epitopes on MuSK at the neuromuscular junction; this inhibits a pathway that clusters the acetylcholine (neurotransmitter) receptors and leads to failure of neuromuscular transmission. In vitro Fab-arm exchange-inducing conditions were applied to MuSK antibodies in sera, purified IgG4 and IgG1-3 sub-fractions. Solid-phase cross-linking assays were established to determine the extent of pre-existing and inducible Fab-arm exchange. Functional effects of the resulting populations of IgG4 antibodies were determined by measuring inhibition of agrin-induced AChR clustering in C2C12 cells. To confirm the results, kappa/kappa, lambda/lambda and hybrid kappa/lambda IgG4s were isolated and tested for MuSK antibodies. At least fifty percent of patients had IgG4, but not IgG1-3, MuSK antibodies that could undergo Fab-arm exchange in vitro under reducing conditions. Also MuSK antibodies were found in vivo that were divalent (monospecific for MuSK). Fab-arm exchange with normal human IgG4 did not prevent the inhibitory effect of serum derived MuSK antibodies on AChR clustering in C2C12 mouse myotubes. The results suggest that a considerable proportion of MuSK IgG4 could already be Fab-arm exchanged in vivo. This was confirmed by isolating endogenous IgG4 MuSK antibodies containing both kappa and lambda light chains, i.e. hybrid IgG4 molecules. These new findings demonstrate that Fab-arm exchanged antibodies are pathogenic. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.
KW - Fab-arm exchange
KW - IgG4
KW - MuSK
KW - Myasthenia gravis
KW - Autoimmunity
KW - THROMBOTIC THROMBOCYTOPENIC PURPURA
KW - HUMAN-IMMUNOGLOBULIN-G
KW - PEMPHIGUS-VULGARIS
KW - ACQUIRED NEUROMYOTONIA
KW - ACETYLCHOLINE-RECEPTOR
KW - NEUROMUSCULAR-JUNCTION
KW - SUBCLASS DISTRIBUTION
KW - LIMBIC ENCEPHALITIS
KW - COMPLEMENT ACTIVATION
KW - IMMUNE-COMPLEXES
U2 - 10.1016/j.jaut.2016.11.005
DO - 10.1016/j.jaut.2016.11.005
M3 - Article
C2 - 27965060
SN - 0896-8411
VL - 77
SP - 104
EP - 115
JO - Journal of Autoimmunity
JF - Journal of Autoimmunity
ER -