Distinctive binding properties of human monoclonal LGI1 autoantibodies determine pathogenic mechanisms

Abstract

Autoantibodies against leucine-rich glioma inactivated 1 (LGI1) are found in patients with limbic encephalitis and focal seizures. Here, we generate patient-derived monoclonal antibodies (mAbs) against LGI1. We explore their sequences and binding characteristics, plus their pathogenic potential using transfected HEK293T cells, rodent neuronal preparations, and behavioural and electrophysiological assessments in vivo after mAb injections into the rodent hippocampus. In live cell-based assays, LGI1 epitope recognition was examined with patient sera (n = 31), CSFs (n = 11), longitudinal serum samples (n = 15), and using mAbs (n = 14) generated from peripheral B cells of two patients. All sera and 9/11 CSFs bound both the leucine-rich repeat (LRR) and the epitempin repeat (EPTP) domains of LGI1, with stable ratios of LRR:EPTP antibody levels over time. By contrast, the mAbs derived from both patients recognized either the LRR or EPTP domain. mAbs against both domain specificities showed varied binding strengths, and marked genetic heterogeneity, with high mutation frequencies. LRR-specific mAbs recognized LGI1 docked to its interaction partners, ADAM22 and ADAM23, bound to rodent brain sections, and induced internalization of the LGI1-ADAM22/23 complex in both HEK293T cells and live hippocampal neurons. By contrast, few EPTP-specific mAbs bound to rodent brain sections or ADAM22/23-docked LGI1, but all inhibited the docking of LGI1 to ADAM22/23. After intrahippocampal injection, and by contrast to the LRR-directed mAbs, the EPTP-directed mAbs showed far less avid binding to brain tissue and were consistently detected in the serum. Post-injection, both domain-specific mAbs abrogated long-term potentiation induction, and LRR-directed antibodies with higher binding strengths induced memory impairment. Taken together, two largely dichotomous populations of LGI1 mAbs with distinct domain binding characteristics exist in the affinity matured peripheral autoantigen-specific memory pools of individuals, both of which have pathogenic potential. In human autoantibody-mediated diseases, the detailed characterization of patient mAbs provides a valuable method to dissect the molecular mechanisms within polyclonal populations.

Study of B Cell Repertoire in Patients With Anti-N-Methyl-D-Aspartate Receptor Encephalitis

“…We analyzed 334 sets of BCR sequence data from patients with MS in the SAR database and searched the CDR3 AA (ARVGSKYGFETFDI) of the most common clone. And we also compared our heavy chain common clone with the data of patients with anti-LGI1 encephalitis ( 20 ) or NMOSD as reported previously ( 21 – 23 ). However, we didn't find the most common clone in the comparison data set.…”

“…The B cells germline database from the international ImMunoGeneTics information system (IMGT) was utilized as reference sequence (30). The four antibody consensus frameworks (FR region, To test whether the heavy chain common clone was specific for anti-NMDAR encephalitis, we used CDR3 AA sequence of patients with anti-LGI1 encephalitis (20), another 90 sets of BCR sequencing data from non-Chinese healthy population, 334 sets of BCR sequencing data from patients with multiple sclerosis (MS), and public CDR3 sequence of anti-aquaporin-4 (AQP4) (21-23) as control. Anti-LGI1 encephalitis, MS, and NMOSD are also autoimmune diseases of the central nervous system (CNS).…”

“…The characteristics of B cell immune repertoire we analyzed include clone cluster, gene family usage preference of variable (V), diversity (D) and joining (J) gene segments, amino acid (AA) characteristics in complementary determining region 3 (CDR3), and antibody mutation rate ( 19 ). We compared the data of patients with anti-NMDAR encephalitis, anti-leucine-rich glioma inactivated 1 (anti-LGI1) encephalitis ( 20 ), multiple sclerosis (MS), neuromyelitis optica spectrum disorder (NMOSD) ( 21 – 23 ), and public healthy controls. We expect our study will help identify potential diagnostic markers and provide clues to explain the pathogenesis of the anti-NMDAR encephalitis.…”

Cognitive impact of neuronal antibodies: encephalitis and beyond

“…The dominant effect of EPTP-binding antibodies, on the other hand, appeared to be disruption of the interaction between LGI1 and its receptors. Both LRR-and EPTP-specific antibodies completely abrogated LTP induction at CA3-CA1 hippocampal synapses, which translated to impairment of recognition memory in mice exposed to LRRP-antibodies 48 . These findings likely explain the amnestic syndrome experienced by patients with LGI1 encephalitis.…”

Stop testing for autoantibodies to the VGKC-complex: only request LGI1 and CASPR2

“…For example, LGI1 antibodies can disrupt interactions between LGI1 and its receptors ADAM22/23, internalise the LGI1–ADAM complex and trigger neuronal hyperexcitability and memory deficits in vivo passive transfer models. 20 21 25 42 There is also clear evidence supporting the pathogenicity of CASPR2 antibodies with rodent passive transfer reproducing human pain manifestations, and evidence that the antibodies can disrupt CASPR2 interactions with contactin-2 22 . 43…”