Idd-linked genetic regulation of TACIhigh expressing B cells in NOD mice

In NOD mice, B cells play a key role in the initiation of type 1 diabetes pathogenesis. We have identified a novel NOD-specific B cell-related trait, i.e. the increased percentage of TACIhigh-expressing splenic B cells, by comparing NOD mice with non-autoimmune C57BL/6 mice. Using athymic NOD mice, we determined that this trait was T cell independent. We mapped the loci contributing to the increased proportion of TACIhigh expressing splenic B cells and found that the control of TACI expression was strongly linked to chromosome 1, in a region which includes the insulin-dependent diabetes (Idd) 5 loci. Moreover, another locus potentially involved was detected in the vicinity of Idd22 on chromosome 8. Interestingly, when analyzing age-dependent contribution to the obtained LOD scores we observed that the linkage to chromosome 8 was explained solely by mice ≥61 days of age, suggesting a temporal genetic regulation of TACI expression. In addition, analysis of genetic interaction between chromosome 1 and chromosome 8 indicated that the two loci acted in an additive fashion. Our findings corroborate the notion that B cell deviations contribute to type 1 diabetes development, and suggest a temporal regulation of TACIhigh expression, possibly influenced by the ongoing autoimmune process.