Analysis of anti-GM1 ganglioside IgM antibodies cloned from motor neuropathy patients demonstrates diverse V region gene usage with extensive somatic mutation.

Serum anti-GM1 ganglioside Abs are abnormally elevated in patients with chronic motor neuropathies and Guillain-Barré syndrome. We have cloned six anti-GM1 IgM Abs from PBMCs of five affected patients. VH and VL gene analysis demonstrated substantial somatic mutation, predominantly clustered around VH CDR2 and FR3 in all six Abs. The Abs SM1, DO1, and WO1, isolated from three different patients, are encoded by closely related VH gene segments with restricted canonical structures. The corresponding L chains are encoded by V lambda II and V lambda VIII genes and also share the same canonical structures, containing nucleotide deletions at the VL/JL boundary to form a VLCDR3 of 10 amino acids. DO1 and WO1 VH segments show nucleotide identities of 95.6% and 88.8%, respectively, to the VH3 member 1.9III, and SM1 shows 87.8% identity to the closely related VH3 member, Hv3005. The Abs BO1 and BO3, derived from a single patient and containing the same VH-D-JH and VL-JL rearrangements, are encoded by the VH3 gene, HHg19, with nucleotide identities of 92.2 and 91.2%, respectively, and have both common and unique somatic mutations. The VH sequence of BR1 has 91.3% identity to the VH4 member, V71-2. These data indicate that neuropathy-associated anti-GM1 IgM Abs can be encoded by both diverse and closely related V genes in association with restricted canonical structures, and that their V genes are somatically mutated, consistent with an origin through an Ag-driven immune response.