The Journal of Immunology, Vol 157, Issue 2 763-771, Copyright © 1996 by American Association of Immunologists

ARTICLES

Somatically mutated B cell pool provides precursors for insulin antibodies

JW Thomas and C Hulbert
Division of Rheumatology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.

Antibodies to insulin are products of autoreactive B lymphocytes that escape inactivation or clonal deletion and are examples of "clonal ignorance." To understand the genetic origin of Abs from clonally ignorant B cells, the roles of somatic mutation and germ-line V(H) structures were examined for two murine IgG1 mAb that bind human and rodent insulin. Engineered mAb constructs that express germ-line or mutated V(H) genes show that somatic mutations introducing aspartic acid in or adjacent to CDRH2 play a key role in insulin binding. When either of the two anti-insulin V(H) regions is returned to its germ- line (unmutated) sequence, neither mAb binds insulin and the germ-line- encoded mAb are not polyreactive. Reconstruction of the somatic evolution of insulin binding in both mAbs shows that a single mutation in CDRH2 is sufficient to generate anti-insulin activity from a nonbinding precursor. When the role of somatic mutation in the binding of rodent insulin is examined, autoreactivity is associated with single mutations in both Abs. Together these findings indicate that, despite a low mutation frequency, IgG insulin Abs may not be derived directly from germ-line (unmutated) precursors. The requirement for somatic mutation as a prerequisite for measurable insulin binding suggests these Abs have their origin in a previously mutated B cell pool as a consequence of the individual's immune history. Low avidity interaction with endogenous insulin may play a role in selection of these B cells and contribute to the origin of clonal ignorance.

This article has been cited by other articles:

				J. W. Thomas, P. L. Kendall, and H. G. Mitchell The Natural Autoantibody Repertoire of Nonobese Diabetic Mice Is Highly Active J. Immunol., December 1, 2002; 169(11): 6617 - 6624. [Abstract] [Full Text] [PDF]

				C. Hulbert, B. Riseili, M. Rojas, and J. W. Thomas Cutting Edge: B Cell Specificity Contributes to the Outcome of Diabetes in Nonobese Diabetic Mice J. Immunol., November 15, 2001; 167(10): 5535 - 5538. [Abstract] [Full Text] [PDF]

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