Redemption of autoantibodies on anergic B cells by variable-region glycosylation and mutation away from self-reactivity
The best-understood mechanisms for achieving antibody self/non-self discrimination discard self-reactive antibodies before they can be tested for binding microbial antigens, potentially creating holes in the repertoire. Here we provide evidence for a complementary mechanism: retaining autoantibodies in the repertoire displayed as low levels of IgM and high IgD on anergic B cells, masking a varying proportion of autoantibody-binding sites with carbohydrates, and removing their self-reactivity by somatic hypermutation and selection in germinal centers (GCs). Analysis of human antibody sequences by deep sequencing of isotype-switched memory B cells or in IgG antibodies elicited against allogeneic RhD+ erythrocytes, vaccinia virus, rotavirus, or tetanus toxoid provides evidence for reactivation of anergic IgM(low) IgD+ IGHV4-34+ B cells and removal of cold agglutinin self-reactivity by hypermutation, often accompanied by mutations that inactivated an N-linked glycosylation sequon in complementarity-determining region 2 (CDR2). In a Hy10 antibody transgenic model where anergic B cells respond to a biophysically defined lysozyme epitope displayed on both foreign and self-antigens, cell transfers revealed that anergic IgM(low) IgD+ B cells form twice as many GC progeny as naive IgM(hi) IgD+ counterparts. Their GC progeny were rapidly selected for CDR2 mutations that blocked 72% of antigen-binding sites with N-linked glycan, decreased affinity 100-fold, and then cleared the binding sites of blocking glycan. These results provide evidence for a mechanism to acquire self/non-self discrimination by somatic mutation away from self-reactivity, and reveal how varying the efficiency of N-glycosylation provides a mechanism to modulate antibody avidity.
|ISBN||1091-6490 (Electronic) 0027-8424 (Linking)|
|Authors||Sabouri, Z.; Schofield, P.; Horikawa, K.; Spierings, E.; Kipling, D.; Randall, K. L.; Langley, D.; Roome, B.; Vazquez-Lombardi, R.; Rouet, R.; Hermes, J.; Chan, T. D.; Brink, R.; Dunn-Walters, D. K.; Christ, D.; Goodnow, C. C.;|
|Publisher Name||PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA|
|URL link to publisher's version||http://www.ncbi.nlm.nih.gov/pubmed/24821781|
|OpenAccess link to author's accepted manuscript version||https://publications.gimr.garvan.org.au/open-access/12430|