A human anti-insulin IgG autoantibody apparently arises through clonal selection from an insulin-specific "germ-line" natural antibody template: Analysis by V gene segment reassortment and site-directed mutagenesis

Yuji Ichiyoshi, Min Zhou, Paolo Casali

Research output: Contribution to journalArticlepeer-review

43 Scopus citations

Abstract

We analyzed the structural correlates underlying the insulin-dependent selection of the specific anti-insulin IgG1 κ mAb13-producing cell clone, derived from a patient with insulin-dependent diabetes mellitus treated with recombinant human insulin. First, we cloned the germ-line genes that putatively gave rise to the expressed VH and Vκ segments and used them to generate the full (unmutated) "germ-line revertant" of the "wild-type" (somatically mutated) mAb13, using recombinant PCR methods and an in vitro human Cγ1 and Cκ expression system. The full "germ-line revertant" bound insulin specifically and in a dose-saturable fashion, but with a relative avidity (Avrel) more than three-fold lower than that of its wild-type counterpart (Avrel, 1.69 × 10-8vs4.91 × 10-9 g/μl). Second, we established, by reassorting wild-type and germ-line revertant forms of the mAb13 VH and Vκ segments, that the increased Avrel for insulin of mAb13 when compared with its full "germ-line revertant" counterpart was entirely dependent on the mutations in the VH not those in the Vκ chain. Third, we determined, by site-directed mutagenesis experiments, that of the three mutations in the mAb13 VH segment (Ser→Gly, Ser→Thr, and Ser→Arg at positions 31, 56, and 58, respectively), only Arg58 was crucial in increasing the mAb13 Avrel (from 1.44 × 10-8 to 5.14 × 10-9 g/μl) and affinity (Kd, from 189 to 59 nM) for insulin. The affinity enhancement mediated by the VH segment Arg58 residue reflected about a threefold decrease in dissociation rate constant (Koff, from 4.92 × 10-3 to 1.54 × 10-3 s-1) but not an increase in association rate constant (Kon, from 2.60 × 104 to 2.61 × 104 M-1 s-1), and it contrasted with the complete loss of insulin binding resulting from the substitution of the VH segment Asn52 by Lys. The present findings suggest that human insulin, a self Ag, has the potential to recruit a natural autoantibody-producing cell precursor expressing a specific surface receptor for Ag in unmutated configuration, and drive it through affinity maturation. They also show that binding of insulin by such a receptor can be enhanced or completely abrogated by a single amino acid change.

Original languageEnglish (US)
Pages (from-to)226-238
Number of pages13
JournalJournal of Immunology
Volume154
Issue number1
StatePublished - Jan 1 1995
Externally publishedYes

ASJC Scopus subject areas

  • Immunology and Allergy
  • Immunology

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