RFLP analysis of the MHC class III region defines unique haplotypes for the non-obese diabetic, cataract Shionogi and the non-obese non-diabetic mouse strains

Congenic mapping and candidate sequencing of susceptibility genes for Type 1 diabetes in the NOD mouse

Inheritance of type 1 diabetes is polygenic with a major susceptibility gene located in the major histocompatibility complex (MHC). In addition to MHC-linked susceptibility, a number of susceptibility genes have been mapped outside the MHC in both humans and animal models. In order to localize and identify susceptibility genes for type 1 diabetes, we have developed a series of congenic strains in which either susceptibility intervals from the NOD mouse, a mouse model of type 1 diabetes, were introgressed onto control background genes or protective intervals from control strains were introgressed onto NOD background genes. NOD. CTS-H-2 congenic mice, which possess recombinant MHC with NOD alleles at class II A and E genes, which are candidates for Idd1, revealed that Idd1 consists of multiple components, one in class II (Idd1) and the other adjacent to, but distinct from, Idd1 (Idd16). Phenotypes of NOD. IIS-Idd3 congenic mice, which share the same alleles at both Il2 and Il21 as the NOD mouse, were indistinguishable from the NOD parental strain, indicating that both Il2 and Il21 are candidates for Idd3. In contrast, NOD. IIS-Idd10 congenic mice, which share the same alleles at Fcgr1, a previous candidate for Idd10, as the NOD mouse, were protected from type 1 diabetes, suggesting that Fcgr1 may not be responsible for the Idd10 effect. These data suggest that the use of strain colony closely related to a disease model to find the same candidate mutation on different haplotypes and make congenic strains with this recombinant chromosome, termed ancestral haplotype congenic mapping, is an effective strategy for fine mapping and identification of genes responsible for complex traits.

A locus affecting immunoglobulin isotype selection (Igis1) maps to the MHC region in C57BL, BALB/c and NOD mice

We have previously shown that H2b mice with B10 or BALB genetic backgrounds have higher basal levels of IgG2a than H2k and H2d congenic strains and, hence, have low IgG1/IgG2a ratios, which is consistent with a T1 cytokine milieu. The phenotypic marker of the high IgG2a levels, denoted immunoglobulin isotype-1 (Igis1) was provisionally mapped telomeric of IEbeta using MHC recombinant mice. In addition, data from B10.A(2R), B10.A(1R) and B10.A(18R) mice indicated that Igis1 may lie in a 27 kb region between G7b (Sm-X5) and G7c. In the present study we confirm that Igis1 is in the H2 region using BALB and B10 congenic F2 mice. H2bb F2 mice had higher IgG2a levels than the H2dd parental strains. H2bd F1 and F2 mice on the B10 background produced IgG2a levels comparable with the H2bb parental strain, indicating that the b allele was dominant. In contrast, the H2bd F1 and F2 mice on the BALB background produced IgG2a levels between those of the H2bb and H2dd parental strains, indicating codominance of the b and d alleles. This suggests that a background gene influences regulation of IgG2a levels by Igis1. Non-obese diabetic (NOD) mice (KdIAg7IEnu11Db), which can develop type 1 diabetes, had higher levels of IgG2a than NOD-H2d congenic mice. Thus, Igis1 affects isotype selection in the presence of non-MHC diabetes genes. As type 1 diabetes is associated with T1 responses, Igis1 may affect susceptibility to this condition.

A defect in bone marrow derived dendritic cell maturation in the nonobesediabetic mouse

The pathogenesis of diabetes in the nonobese diabetic (NOD) mouse is characterized by a selective destruction of the insulin-producing beta-cells in the islets of Langerhans mediated by autoreactive T cells. The function of T cells is controlled by dendritic cells (DC), which are not only the most potent activators of naïve T cells, but also contribute significantly to the establishment of central and peripheral tolerance. In this study, we demonstrate that the NOD mouse (H2: K(d), Ag(7), E*, D(b)) shows selective phenotypic and functional abnormalities in DC derived from bone marrow progeny cells in response to GM-CSF (DC(NOD)). NOD DC, in contrast to CBA DC, have very low levels of intracellular I-A molecules and cell surface expression of MHC class II, CD80, CD86 and CD40 but normal beta 2-microglobulin expression. Incubation with the strong inflammatory stimulus of LPS and IFN-gamma does not increase class II MHC, CD80 or CD86, but upregulates the level of CD40. The genetic defect observed in the DC(NOD) does not map to the MHC, because the DC from the MHC congenic NOD.H2(h4) mouse (H2: K(k), A(k), E(k), D(k)) shares the cell surface phenotype of the DC(NOD). DC from these NOD.H2(h4) also fail to present HEL or the appropriate HEL-peptide to an antigen-specific T cell hybridoma. However all the DC irrespective of origin were able to produce TNF-alpha, IL-6, low levels of IL-12(p70) and NO in response to LPS plus IFN-gamma. A gene or genes specific to the NOD strain, but outside the MHC region, therefore must regulate the differentiation of DC in response to GM-CSF. This defect may contribute to the complex genetic aetiology of the multifactorial autoimmune phenotype of the NOD strain.

Identification of a sialidase encoded in the human major histocompatibility complex

Mammalian sialidases are important in modulating the sialic acid content of cell-surface and intracellular glycoproteins. However, the full extent of this enzyme family and the physical and biochemical properties of its individual members are unclear. We have identified a novel gene, G9, in the human major histocompatibility complex (MHC), that encodes a 415-amino acid protein sharing 21-28% sequence identity with the bacterial sialidases and containing three copies of the Asp-block motif characteristic of these enzymes. The level of sequence identity between human G9 and a cytosolic sialidase identified in rat and hamster (28-29%) is much less than would be expected for analogous proteins in these species, suggesting that G9 is distinct from the cytosolic enzyme. Expression of G9 in insect cells has confirmed that it encodes a sialidase, which shows optimal activity at pH 4.6, but appears to have limited substrate specificity. The G9 protein carries an N-terminal signal sequence and immunofluorescence staining of COS7 cells expressing recombinant G9 shows localization of this sialidase exclusively to the endoplasmic reticulum. The location of the G9 gene, within the human MHC, corresponds to that of the murine Neu-1 locus, suggesting that these are analogous genes. One of the functions attributed to Neu-1 is the up-regulation of sialidase activity during T cell activation.

Genetic requirements for acceleration of diabetes in non-obese diabetic mice expressing interleukin-2 in islet beta-cells

Diabetes was dramatically accelerated in non-obese diabetic (NOD) transgenic mice that expressed interleukin-2 (IL-2) in their beta cells. A single cross to C57BL/6 completely prevented this effect and a further backcross to the NOD genetic background showed that at least two diabetes susceptibility loci (Idd1s and Idd3/10s) were required for the diabetes acceleration T cells activated to islet antigens were not circulating in the mice. The accelerating effect of IL-2 was present; but decreased, in NOD mice that lacked CD8+ T cells as well as in NOD SCID mice. The implications are that in the NOD genetic background, the production of cytokines, such as IL-2, by islet-specific CD4+ T cells can lead to beta cell damage and diabetes and that CD8+ T cells may have a role in accelerating diabetes onset.

Pulsed field gel electrophoretic analysis of the rat major histocompatibility complex class III region shows extensive inter-species conservation

Using pulsed field gel electrophoresis (PFGE), we have examined the rat major histocompatibility complex (MHC) for the presence of a number of new class III region genes recently identified in the human MHC. We find homologous genes to the human G1, G2, G4, G7a, G9, G9a, G10, G13, G15, and G18 genes, but not the G8 gene in the rat genome, and show that these are linked to the rat TNF-alpha and C4/Slp loci. A long-range restriction map has been constructed on the basis of a PFGE analysis which demonstrates extensive co-linearity in the positions of the homologous sequences in the region between the C4/Slp and TNF loci in the rat MHC when compared with that of the human MHC class III region.