Genetic and Functional Analysis of theNkt1Locus Using Congenic NOD Mice

Abstract

Defective invariant natural killer T-cells (iNKT cells) havebeen implicated in the etiology of type 1 diabetes in nonobese diabetic (NOD) mice. In a genome scan of a cross between NOD and C57BL/6 mice, the most significant locus controlling the number of iNKT cells, referred to as Nkt1, was recently mapped to distal chromosome 1. Here, using congenic mice for this chromosomal segment, we definitively demonstrate the existence of Nkt1 and show that introgression of the C57BL/6 allele onto the NOD background improves both the number of iNKT cells and their rapid production of cytokines elicited by ␣-galactosylceramide treatment, explaining at least half of the difference between the NOD and C57BL/6 strains. Using new subcongenic lines, we circumscribed the Nkt1 locus to a 8.7-cM segment, between the NR1i3 and D1Mit458 markers, that notably includes the SLAM (signaling lymphocytic activation molecule) gene cluster, recently involved in murine lupus susceptibility. However, despite a significant correction of the iNKT cell defect, the Nkt1 locus did not alter the course of spontaneous diabetes in congenic mice. Our findings indicate a complex relationship between iNKT cells and autoimmune susceptibility. Congenic lines nonetheless provide powerful models to dissect the biology of iNKT cells.

Enhanced Early Expansion and Maturation of Semi-Invariant NK T Cells Inhibited Autoimmune Pathogenesis in Congenic Nonobese Diabetic Mice

“…In contrast, it was reported that the Slamf1 expression in NOD thymocytes was low, suggesting an association of iNKT cell deficiency with Slamf1 locus on chromosome 1 (39). iNKT cell development was partially improved in NOD mice congenic for B6 allele of Slamf1 locus, however, the improvement did not alter T1D pathogenesis (35). It is possible that a high level of Slamf1 signal enhances positive selection of iNKT cells, but not their regulatory function.…”

“…These studies indicated that iNKT cell deficiency is a result of complex interplay among different factors. However, these studies did not provide evidence for the connection between T1D susceptibility and iNKT cell deficiency (18,(33)(34)(35). For instance, T1D incidence was reduced in NOD mice congenic for the Idd6 locus of the B6 allele, but the development of iNKT cells was still defective in these mice (33).…”

“…For instance, T1D incidence was reduced in NOD mice congenic for the Idd6 locus of the B6 allele, but the development of iNKT cells was still defective in these mice (33). In contrast, development and cytokine production of iNKT cells were partially recovered in NOD.NKT1 mice (congenic for a B6-derived Nkt1 allele) that developed T1D as frequently as NOD mice (35), suggesting that Nkt1 locus does not encode T1D susceptibility and that incomplete restoration of iNKT cell functions could not provide T1D protection. Alternatively, it is possible that these observations argued against the linkage between T1D susceptibility and iNKT cell deficiency.…”

Influence of a Non-NK Complex Region of Chromosome 6 on CD4+ Invariant NK T Cell Homeostasis

“…Investigations in genetically modified NOD mice harboring either increased numbers of iNKT cells as compared with wild-type NOD mice, or no iNKT cells brought discrepant data. Transgenic mice for a V␣14-J␣18 TCR containing high levels of iNKT cells (14) were protected, and introgression of the C57BL/6 Nkt1 locus corrected the iNKT cell defects but did not alter the course of spontaneous diabetes (21). Diabetes incidence was found either increased (16,30) or unchanged (19,31) in CD1d-deficient NOD mice, and no effect was observed in J␣18-deficient mice (Ref.…”

“…A genome-wide screen of a cross between NOD and C57BL/6 mice identified two major loci controlling iNKT cell number: Nkt1 on distal chromosome 1, and Nkt2 on chromosome 2 that overlaps with the insulin-dependent diabetes susceptibility locus Idd13 (20,21). iNKT cell abnormalities in NOD mice were clearly shown to be independent of Idd1, Idd3, Idd11, and Idd17/10/18 regions (22,23), but some controversy remains concerning Idd5 and Idd9 (22,24).…”