Congenic analysis of the NKT cell control gene Nkt2 implicates the peroxisomal protein Pxmp4.

Type 1 NKT cells play a critical role in controlling the strength and character of adaptive and innate immune responses. We have previously reported deficiencies in the numbers and function of NKT cells in the NOD mouse strain, which is a well-validated model of type 1 diabetes and systemic lupus erythematosus. Genetic control of thymic NKT cell numbers was mapped to two linkage regions: Nkt1 on distal chromosome 1 and Nkt2 on chromosome 2. Herein, we report the production and characterization of a NOD.Nkrp1(b).Nkt2b(b) congenic mouse strain, which has increased thymic and peripheral NKT cells, a decreased incidence of type 1 diabetes, and enhanced cytokine responses in vivo and increased proliferative responses in vitro following challenge with alpha-galactosylceramide. The 19 highly differentially expressed candidate genes within the congenic region identified by microarray expression analyses included Pxmp4. This gene encodes a peroxisome-associated integral membrane protein whose only known binding partner is Pex19, an intracellular chaperone and component of the peroxisomal membrane insertion machinery encoded by a candidate for the NKT cell control gene Nkt1. These findings raise the possibility that peroxisomes play a role in modulating glycolipid availability for CD1d presentation, thereby influencing NKT cell function.

Interactions between B-lymphocytes and type 1 NKT cells in autoimmune diabetes.

Type 1 diabetes is one of the most prevalent autoimmune conditions that develops during childhood and has an increasing incidence worldwide. The disease results from the destruction of pancreatic beta cells mediated by autoreactive T-lymphocytes. In order to develop preventive therapies, the cellular mechanisms responsible for the generation and activation of beta cell-specific T-lymphocytes need to be characterized. Recent studies in the NOD mouse model of autoimmune diabetes suggest that the MHC Class II presentation of beta cell-derived antigens by B-lymphocytes could support the development and activity of autoreactive CD4+ T-lymphocytes in this disease. Interestingly, B-lymphocytes are also the most frequent antigen presenting cells expressing the MHC Class I like molecule, CD1d, the restriction molecule responsible for presentation of lipid and glycolipid antigens to Type 1 NKT cells. Splenic marginal zone B-lymphocytes, which express CD1d at particularly high levels, seem poised to signal to Type 1 NKT cells. In contrast to the disease-promoting role of conventional CD4+ T-lymphocytes, several lines of evidence have shown that Type 1 NKT cells are involved in the prevention of Type 1 Diabetes. This review will analyze current knowledge on the roles of B-lymphocytes and Type 1 NKT cells in the onset of Type 1 Diabetes and explore possible outcomes of their interactions in relation to disease.