SummaryInsulin-dependent diabetes meUitus (IDDM) in NOD/Lt mice represents a complex polygenic disease. NOR/Lt is a recombinant congenic strain (RCS) in which limited regions of the NOD/Lt genome have been replaced by genome from the C57BL/KsJ strain. NOR. mice are insulitis resistant and diabetes free despite genetic identity with NOD at numerous chromosomal regions containing previously described insulin-dependent diabetes (Idd) genes, including the strongly diabetogenic H2g 7 major histocompatibility complex (MHC) haplotype. The present study revealed BKs-derived genome on segments of chromosomes (Chr) 1, 2, 4, 5, 7, 11, 12, and 18, approximating 11.6% of the total NOR genome analyzed. (NOD x NOR)F2 segregation analysis was employed to identify chromosomal regions in NOR containing Idd resistance alleles. IDDM developed in 33% (10/30) of F1 females, and 29.3% (36/123) of F2 females aged to 1 yr. A previously unrecognized diabetes resistance locus (designated Idcl13") strongly protective in homozygous state was identified on NOR Chr 2 in linkage with the Illcr structural gene. The existence of this locus was confirmed by construction of a NOD stock congenic for NORderived markers on Chr 2. Our analysis shows the utility of RCS and congenic stocks for the identification and isolation of non-MHC genes with strong antidiabetogenic functions.

Carboxypeptidase D (CPD) is a recently described 180-kD enzyme with carboxypeptidase E-like enzymatic properties. CPD has been proposed to be present in the secretory pathway and to contribute to peptide hormone processing in the Cpe(fat)/Cpe(fat) mouse, which lacks functional CPE. Sequence analysis of cDNA clones encoding rat CPD show the protein to contain an amino-terminal signal peptide, three carboxypeptidase-like domains, a putative transmembrane domain, and a 60-amino-acid cytoplasmic tail. Whereas active site, substrate-binding, and metal-binding residues of other metallocarboxypeptidases are conserved in the first two domains of CPD, several of the critical residues are not conserved in the third domain; this third domain is not predicted to form an active carboxypeptidase. The overall homology between rat CPD and the duck homolog gp180 is high, with 75% amino acid identity. The three carboxypeptidase domains show 66%, 83%, and 82% amino acid identity between rat CPD and duck gp180. Homology is also high in the transmembrane domain (86%) and in the cytoplasmic tail (97%). The mouse Cpd gene maps to the medial portion of chromosome 11, approximately 45.5 cM distal to the centromere. Northern blot analysis of CPD mRNA shows major bands of approximately 8 and 4 kb in many rat tissues, and additional species ranging from 1.4 to 5 kb that are expressed in some tissues or cell lines. CPD mRNA is detectable in most tissues examined, and is most abundant in hippocampus, spinal cord, atrium of the heart, colon, testis, and ovaries. In situ hybridization of CPD mRNA shows a distribution in many cells in rat brain and other tissues, with high levels in hippocampus, olfactory bulb, and the intermediate pituitary. The broad distribution is consistent with a role for CPD in the processing of many peptides and proteins that transit the secretory pathway.

Several lines of evidence point to abnormalities of the phenotype, cytokine responses, and function of cells of the myeloid lineage in non-obese diabetic (NOD) mice. In this study we have characterized the phenotype and myeloid progenitor function of NOD bone marrow. Two hematopoietic differentiation antigens, Ly-6C and AA4.1, are expressed abnormally on NOD bone marrow cells. While multilineage erythromyeloid progenitor cells (day 12 CFU-S) are normal in number in NOD mice, more differentiated myeloid progenitors are deficient in their in vitro responses to IL-3, granulocyte/macrophage colony-stimulating factor (GM-CSF), and IL-5. Since the diabetes-predisposing Idd-5 gene of NOD mice maps close to the IL-1 receptor, we tested NOD bone marrow cells for a defect in synergy between IL-1 and IL-3; no defect was found. The defects in myelopoiesis described here may predispose the NOD mouse to autoimmunity by impairing macrophage maturation.

Although expressed at very low levels in islets of NOD mice, GAD65 is a candidate islet autoantigen. Two transgenic lines of NOD/Lt mice expressing high levels of human GAD65 from a rat insulin promoter were generated. Transgenes were integrated on proximal chromosome 15 of the A line and on the Y chromosome of the Y line. Transgenic A-line mice were obligate hemizygotes, since homozygous expression resulted in developmental lethality. A twofold higher level of hGAD65 transcripts in A-line islets from young donors was associated with higher GAD protein and enzyme activity levels. Y-line males developed diabetes at a similar rate and incidence as standard NOD/Lt males. In contrast, A-line mice of both sexes exhibited a markedly lowered incidence of diabetes. Insulitis, present in both transgenic lines, developed more slowly in A-line mice and correlated with a reduction in the ratio of gamma-interferon to interleukin-10 transcripts. Splenic leukocytes from young A-line donors transferred diabetes into NOD-scid recipients at a retarded rate compared with those from nontransgenic donors. Further, nontransgenic NOD T-cells transferred diabetes more slowly in NOD-scid recipients that were congenic for A-line transgenes as compared with standard NOD-scid recipients. Primed T-cell responses and spontaneous humoral reactivity to GAD65 failed to distinguish transgenic from nontransgenic mice. Quantitative differences in expression level or insertional mutagenesis are possible mechanisms of protection in the A line.

The murine alloantigen, Ly‐6C, is found on 45% of bone marrow cells, 25% of splenocytes and 15% of lymph node cells in all inbred strains of mice tested, with the exception of NOD, NZB and ST. In these three strains, Ly‐6C expression can be detected on only 5% of bone marrow cells and not at all on cells from spleen or lymph node. NOD and NZB, which are models for the autoimmune diseases, diabetes and lupus, respectively, also exhibit a depressed syngeneic mixed lymphocyte reaction. Southern blot analysis reveals a restriction fragment length polymorphism involving the Ly‐6C gene which is unique to these three strains. Cloning of the affected genomic segment from the NOD mouse indicates the presence of an interruption in the flanking region of the Ly‐6C gene at a point 475 bp upstream of the transcription initiation site and the consequent separation of distal 5′ sequences from the body of the gene by at least 10 kb. Inspection of the recombination borders reveals a set of inverted copies of a mouse repetitive R element. Transfection of the Ly‐6C genes from NOD and BALB/c into a murine carcinoma line indicates relative functional impairment of the NOD gene, thus paralleling performance in vivo.