Use of the most JH-proximal human Ig H chain V region gene, VH6, in the expressed immune repertoire
Varade, W.S.; Marin, E.; Kittelberger, A.M.; Insel, R.A.
Journal of Immunology 150(11): 4985-4995
1993
ISSN/ISBN: 0022-1767 PMID: 8496600 Document Number: 412668
V-H6, the most 3' human H chain V region gene, is preferentially expressed in the preimmune repertoire of the developing human fetus. To determine whether V-H6 contributes to the immune repertoire, we amplified and sequenced from human spleen RNA V-H6 rearrangements that were isotype-switched to IgG. Eighteen distinct in-frame V-H6 clones were sequenced. Definitive assignment to C-gamma-1 could be made in the majority of clones, and all had undergone extensive somatic hypermutation in the V region with an average of 14 (range, 2 to 25) mutations/281 bp in the V-H6 segment. The overall frequency of somatic mutation was 5.2% of the total nucleotides sequenced. Replacement somatic mutations were targeted to the complementarity determining region, and the complementarity determining region had higher replacement to silent mutation ratios, consistent with antigenic selection. Silent somatic mutations were also significantly more frequent in the complementarity determining region compared to the framework region. Five clones were derived from the same V-H6D-xp'1J-H6 rearrangement, each containing unique and shared mutations. All D-H segments used by independently arising clones were unique, and all D-H reading frames were seen. N segments were lacking at either the 5'D-H-J-H junction or the 3'D-H-J-H junction in 7 of 13 independent rearrangements. D-H-D-H recombinations were frequently observed, and there was biased usage of J-H3b and J-H4b in the clones. The data imply that a high degree of diversity arises from use of this 3'-VH gene in the immune repertoire.