Allotype-associated variation in the human gamma3 switch region as a basis for differences in IgG3 production.
High and low serum concentrations of IgG3 are associated with the human G3 m(b) and G3 m(g) allotypes, respectively. We previously hypothesized that a low frequency of switching is the most likely defect in (g) allotype-positive individuals, and therefore analyzed the structure, recombination breakpoints, and binding of nuclear proteins to the switch (S)gamma3 regions of these two allotypes. There are no allotype-associated differences in the length and basic structure of the Sgamma3, since both contain eighteen 79-bp repeats. However, we found a number of allotype-associated nucleotide changes. As in the mouse system, there is a preferential switching to the B site, or switch nuclear protein/nuclear factor-kappaB motif, with a clustering of switch breakpoints at the most 5' residue of the B site. The B site sequence used most frequently in switching was found to be mutated at this nucleotide in the (g) allotype-associated Sgamma3. This change was shown by electrophoretic mobility shift assay to alter the binding of the switch nuclear protein/nuclear factor-kappaB protein to the B site. Taken together, these data suggest that polymorphism within Sgamma3 may contribute to allotype-associated differences in IgG3 switching, and that specific sequences within the Sgamma3 79-bp repeats could be mechanistically important for switch recombination.
Pan
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Q
Department of Clinical Immunology and Center for BioTechnology, NOVUM Karolinska Institute at Huddinge Hospital, Sweden. qiang.pan@csb.ki.se
Rabbani
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H
Mills
F C
FC
Severinson
E
E
Hammarström
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L
D000818:Animals; D001483:Base Sequence; D004586:Electrophoresis; D006801:Humans; D007126:Immunoglobulin Allotypes; D007074:Immunoglobulin G / Q000096:biosynthesis*; D007134:Immunoglobulin Switch Region; D051379:Mice; D008969:Molecular Sequence Data; D009705:Nucleosides / Q000032:analysis; D011110:Polymorphism, Genetic
D007126:Immunoglobulin Allotypes; D007074:Immunoglobulin G; D009705:Nucleosides