Diabetes segregates as a single locus in crosses between inbred BB rats prone or resistant to diabetes

Diabetic Rodent Models for Chronic Stroke Studies

Chronic diabetes may cause secondary complications like stroke and also increase post-stroke brain damage. In stroke research, the Stroke Therapy Academic Industry Roundtable (STAIR) identified criteria to increase translational value of preclinical studies, which highlighted the importance of using animal models of comorbidities. Numerous animal models have been used to study the aggravation of ischemic brain damage in diabetics. In this chapter, we discuss rat and mouse models of streptozotocin (STZ)-induced diabetes, with an efficient method provided. We also provide an overview of spontaneously diabetic rodent models. We present different pathophysiological features of diabetes in each rodent model along with the advantages and disadvantages of each model. Utilizing these models may aid the advancement of novel treatments and therapies to lower ischemic brain damage in patients of diabetes.

The Vbeta13 T Cell Receptor Monoclonal Antibody Reduces Hyaluronan and CD68+, CD3+, and CD8+ Cell Infiltrations to Delay Diabetes in Congenic BB DRLyp/Lyp Rats

The depleting Vβ13a T cell receptor monoclonal antibody (mAb) 17D5 prevents both induced and spontaneous autoimmune diabetes in BB rats. Here it was tested in congenic DRLyp/Lyp rats, all of which spontaneously developed diabetes. Starting at 40 days of age, rats were injected once weekly with either saline, His42 Vβ16 mAb, or 17D5 mAb and monitored for hyperglycemia. Diabetes occurred in 100% (n = 5/5) of saline-treated rats (median age, 66 days; range 55-73), and in 100% (n = 6/6) of His42-treated rats (median age, 69 days; range 59-69). Diabetes occurred in fewer (n = 8/11, 73%) 17D5-treated rats at a later age (median 76 days, range 60-92). Three (27%) of the 17D5-treated rats were killed at 101-103 days of age without diabetes (17D5 no-diabetes rats). Survival analysis demonstrated that 17D5 mAb delayed diabetes onset. Saline- and His42-treated rats had severely distorted islets with substantial loss of insulin-positive cells. These rats exhibited prominent hyaluronan (HA) staining, with the intra-islet HA+ accumulations measuring 5,000 ± 2,400 µm2 and occupying 36 ± 12% of islet area, and severe (grade 4) insulitis with abundant infiltration by CD68+, CD3+, and CD8+ cells. The 17D5 mAb-treated rats with delayed diabetes onset exhibited less severe insulitis (predominantly grade 3). In contrast, the 17D5 no-diabetes rats had mostly normal islets, with insulin+ cells representing 76 ± 3% of islet cells. In these rats, the islet HA deposits were significantly smaller than in the diabetic rats; the intra-islet HA+ areas were 1,200 ± 300 µm2 and accounted for 8 ± 1% of islet area. Also, islet-associated CD68+ and CD3+ cells occurred less frequently (on average in 60 and 3% of the islets, respectively) than in the diabetes rats (present in >95% of the islets). No CD8+ cells were detected in islets in all 17D5 no-diabetes rats. We conclude that mAb 17D5 delayed diabetes in DRLyp/Lyp rats and markedly reduced expression of HA and concomitant infiltration of CD68+, CD3+, and CD8+ cells. Our findings underscore the importance of refining immune suppression in prevention or intervention clinical trials to use mAb reagents that are directed against specific T cell receptors.

Autoimmune Diabetes: An Overview of Experimental Models and Novel Therapeutics

Type 1 diabetes (T1D) results from a chronic and selective destruction of insulin-secreting β-cells within the islets of Langerhans of the pancreas by autoreactive CD4(+) and CD8(+) T lymphocytes. The use of animal models of T1D was instrumental for deciphering the steps of the autoimmune process leading to T1D. The non-obese diabetic (NOD) mouse and the bio-breeding (BB) rat spontaneously develop the disease similar to the human pathology in terms of the immune responses triggering autoimmune diabetes and of the genetic and environmental factors influencing disease susceptibility. The generation of genetically modified models allowed refining our understanding of the etiology and the pathogenesis of the disease. In the present review, we provide an overview of the experimental models generated and used to gain knowledge on the molecular and cellular mechanisms underlying the breakdown of self-tolerance in T1D and the progression of the autoimmune response. Immunotherapeutic interventions designed in these animal models and translated into the clinical arena in T1D patients will also be discussed.

Iddm30 controls pancreatic expression of Ccl11 (Eotaxin) and the Th1/Th2 balance within the insulitic lesions

The autoimmune diabetic syndrome of the BioBreeding diabetes-prone (BBDP) rat is a polygenic disease that resembles in many aspects human type 1 diabetes (T1D). A successful approach to gain insight into the mechanisms underlying genetic associations in autoimmune diseases has been to identify and map disease-related subphenotypes that are under simpler genetic control than the full-blown disease. In this study, we focused on the β cell overexpression of Ccl11 (Eotaxin), previously postulated to be diabetogenic in BBDR rats, a BBDP-related strain. We tested the hypothesis that this trait is genetically determined and contributes to the regulation of diabetes in BBDP rats. Similar to the BBDR strain, we observed a time-dependent, insulitis-independent pancreatic upregulation of Ccl11 in BBDP rats when compared with T1D-resistant ACI.1u.lyp animals. Through linkage analysis of a cross-intercross of these two parental strains, this trait was mapped to a region on chromosome 12 that overlaps Iddm30. Linkage results were confirmed by phenotypic assessment of a novel inbred BBDP.ACI-Iddm30 congenic line. As expected, the Iddm30 BBDP allele is associated with a significantly higher pancreatic expression of Ccl11; however, the same allele confers resistance to T1D. Analysis of islet-infiltrating T cells in Iddm30 congenic BBDP animals revealed that overexpression of pancreatic Ccl11, a prototypical Th2 chemokine, is associated with an enrichment in Th2 CD4+ T cells within the insulitic lesions. These results indicate that, in the BBDP rat, Iddm30 controls T1D susceptibility through both the regulation of Ccl11 expression in β cells and the subsequent Th1/Th2 balance within islet-infiltrating T lymphocytes.

Increased GABA(A) channel subunits expression in CD8(+) but not in CD4(+) T cells in BB rats developing diabetes compared to their congenic littermates

GABA (γ-aminobutyric acid), the main inhibitory neurotransmitter in the central nervous system is also present in the pancreatic islet β cells where it may function as a paracrine molecule and perhaps as an immunomodulator of lymphocytes infiltrating the pancreatic islet. We examined CD4(+) and CD8(+) T cells from diabetes prone (DR(lyp/lyp)) or resistant (DR(+/+)) congenic biobreeding (BB) rats for expression of GABA(A) channels. Our results show that BB rat CD4(+) and CD8(+) T cells express α1, α2, α3, α4, α6, β3, γ1, δ, ρ1 and ρ2 GABA(A) channel subunits. In CD8(+) T cells from DR(lyp/lyp) animals the subunits were significantly upregulated relative to expression levels in the CD8(+) T cells from DR(+/+) rats as well as from CD4(+) T cells from both DR(lyp/lyp) and DR(+/+) rats. Functional channels were formed in the T cells and physiological concentrations of GABA (100 nM) decreased T cell proliferation. Our results are consistent with the hypothesis that GABA in the islets of Langerhans may diminish inflammation by inhibition of activated T lymphocytes.

Differential effects of leptin receptor mutation on male and female BBDR Gimap5-/Gimap5- spontaneously diabetic rats

Rodents homozygous for autosomal leptin receptor gene mutations not only become obese, insulin resistant, and hyperleptinemic but also develop a dysregulated immune system. Using marker-assisted breeding to introgress the Koletsky rat leptin receptor mutant (lepr-/lepr-), we developed a novel congenic BBDR.(lepr-/lepr-) rat line to study the development of obesity and type 2 diabetes (T2D) in the BioBreeding (BB) diabetes-resistant (DR) rat. While heterozygous lepr (-/+) or homozygous (+/+) BBDR rats remained lean and metabolically normal, at 3 wk of age all BBDR.(lepr-/lepr-) rats were obese without hyperglycemia. Between 45 and 70 days of age, male but not female obese rats developed T2D. We had previously developed congenic BBDR.(Gimap5-/Gimap5-) rats, which carry an autosomal frameshift mutation in the Gimap5 gene linked to lymphopenia and spontaneous development of type 1 diabetes (T1D) without sex differences. Because the autoimmune-mediated destruction of pancreatic islet beta-cells may be affected not only by obesity but also by the absence of leptin receptor signaling, we next generated BBDR.(lepr-/lepr-,Gimap5-/Gimap5-) double congenic rats carrying the mutation for Gimap5 and T1D as well as the Lepr mutation for obesity and T2D. The hyperleptinemia rescued end-stage islets in BBDR.(lepr-/lepr-,Gimap5-/Gimap5-) congenic rats and induced an increase in islet size in both sexes, while T1D development was delayed and reduced only in females. These results demonstrate that obesity and T2D induced by introgression of the Koletsky leptin receptor mutation in the BBDR rat result in islet expansion associated with protection from T1D in female but not male BBDR.(lepr-/lepr-,Gimap5-/Gimap5-) congenic rats. BBDR.(lepr-/lepr-,Gimap5-/Gimap5-) congenic rats should prove valuable to study interactions between lack of leptin receptor signaling, obesity, and sex-specific T2D and T1D.

Sequence variation and expression of the Gimap gene family in the BB rat

Positional cloning of lymphopenia (lyp) in the BB rat revealed a frameshift mutation in Gimap5, a member of at least seven related GTPase Immune Associated Protein genes located on rat chromosome 4q24. Our aim was to clone and sequence the cDNA of the BB diabetes prone (DP) and diabetes resistant (DR) alleles of all seven Gimap genes in the congenic DR.lyp rat line with 2 Mb of BB DP DNA introgressed onto the DR genetic background. All (100%) DR.^lyp/lyp rats are lymphopenic and develop type 1 diabetes (T1D) by 84 days of age while DR.^+/+ rats remain T1D and lyp resistant. Among the seven Gimap genes, the Gimap5 frameshift mutation, a mutant allele that produces no protein, had the greatest impact on lymphopenia in the DR.^lyp/lyp rat. Gimap4 and Gimap1 each had one amino acid substitution of unlikely significance for lymphopenia. Quantitative RT-PCR analysis showed a reduction in expression of all seven Gimap genes in DR.^lyp/lyp spleen and mesenteric lymph nodes when compared to DR.^+/+. Only four; Gimap1, Gimap4, Gimap5, and Gimap9 were reduced in thymus. Our data substantiates the Gimap5 frameshift mutation as the primary defect with only limited contributions to lymphopenia from the remaining Gimap genes.

Genetic dissection reveals diabetes loci proximal to the gimap5 lymphopenia gene

Congenic DRF.(f/f) rats are protected from type 1 diabetes (T1D) by 34 Mb of F344 DNA introgressed proximal to the gimap5 lymphopenia gene. To dissect the genetic factor(s) that confer protection from T1D in the DRF.(f/f) rat line, DRF.(f/f) rats were crossed to inbred BBDR or DR.(lyp/lyp) rats to generate congenic sublines that were genotyped and monitored for T1D, and positional candidate genes were sequenced. All (100%) DR.(lyp/lyp) rats developed T1D by 83 days of age. Reduction of the DRF.(f/f) F344 DNA fragment by 26 Mb (42.52-68.51 Mb) retained complete T1D protection. Further dissection revealed that a 2 Mb interval of F344 DNA (67.41-70.17 Mb) (region 1) resulted in 47% protection and significantly delayed onset (P < 0.001 compared with DR.(lyp/lyp)). Retaining <1 Mb of F344 DNA at the distal end (76.49-76.83 Mb) (region 2) resulted in 28% protection and also delayed onset (P < 0.001 compared with DR.(lyp/lyp)). Comparative analysis of diabetes frequency in the DRF.(f/f) congenic sublines further refined the RNO4 region 1 interval to approximately 670 kb and region 2 to the 340 kb proximal to gimap5. All congenic DRF.(f/f) sublines were prone to low-grade pancreatic mononuclear cell infiltration around ducts and vessels, but <20% of islets in nondiabetic rats showed islet infiltration. Coding sequence analysis revealed TCR Vbeta 8E, 12, and 13 as candidate genes in region 1 and znf467 and atp6v0e2 as candidate genes in region 2. Our results show that spontaneous T1D is controlled by at least two genetic loci 7 Mb apart on rat chromosome 4.

PolyI:C induction of diabetes is controlled by Iddm4 in rats with a full regulatory T cell pool

The Iddm4 gene controls diabetes in rats depleted of regulatory T cells (T reg) and immune-activated via treatment with the toll-like receptor 3 (TLR-3) ligand, polyI:C. Both diabetes-resistant (BBDR) and diabetes-prone (BBDP) BB rats carry dominant permissive alleles of Iddm4, while the recessive Wistar Furth (WF) rat allele is protective. Iddm4 is positioned close to Iddm2 on chromosome 4, but when we introgressed BBDP-derived parts of this region--either containing both genes or Iddm2 alone--into the WF genome, none of these congenic strains developed spontaneous diabetes. Although both strains harbor two copies of the recessive Iddm2 allele of the BBDP rat, making these animals devoid of T reg cells, immune activation in itself via polyI:C treatment did not induce overt diabetes. Interestingly, TLR-3 ligation without depletion of T regs resulted in diabetes and insulitis development in nonlymphopenic F1-offspring of mating the Iddm4+Iddm2 congenic strain to WF. This demonstrates that the diabetogenic allele of Iddm4 is able to confer diabetes susceptibility even in a nonlymphopenic host with a full T reg pool, and that homozygosity for Iddm2--although responsible for an almost total lack of T regs-delays the disease process. Finally, we have confirmed the position of Iddm4 in truly congenic strains.

Low-density cells isolated from the rat thymus resemble branched cortical macrophages and have a reduced capability of rescuing double-positive thymocytes from apoptosis in the BB-DP rat

Biobreeding-diabetes prone (BB-DP) rats spontaneously develop organ-specific autoimmunity and are severely lymphopenic and particularly deficient in ART2(+) regulatory T cells. A special breed, the so-called BB-diabetic-resistant (DR) rats, are not lymphopenic and do not develop organ-specific autoimmunity. The genetic difference between both strains is the lymphopenia (lyp) gene. Intrathymic tolerance mechanisms are important to prevent autoimmunity, and next to thymus epithelial cells, thymus APC play a prominent part in this tolerance. We here embarked on a study to detect defects in thymus APC of the BB-DP rat and isolated thymus APC using a protocol based on the low-density and nonadherent character of the cells. We used BB-DP, BB-DR, wild-type F344, and F344 rats congenic for the lyp gene-containing region. The isolated thymus, nonadherent, low-density cells appeared to be predominantly ED2(+) branched cortical macrophages and not OX62(+) thymus medullary and cortico-medullary dendritic cells. Functionally, these ED2(+) macrophages were excellent stimulators of T cell proliferation, but it is more important that they rescued double-positive thymocytes from apoptosis. The isolated thymus ED2(+) macrophages of the BB-DP and the F344.lyp/lyp rat exhibited a reduced T cell stimulatory capacity as compared with such cells of nonlymphopenic rats. They had a strongly diminished capability of rescuing thymocytes from apoptosis (also of ART2(+) T cells) and showed a reduced Ian5 expression (as lyp/lyp thymocytes do). Our experiments strongly suggest that branched cortical macrophages play a role in positive selection of T cells in the thymus and point to defects in these cells in BB-DP rats.

Introgression of F344 rat genomic DNA on BB rat chromosome 4 generates diabetes-resistant lymphopenic BB rats

Failure to express the Gimap5 protein is associated with lymphopenia (lyp) and linked to spontaneous diabetes in the diabetes-prone BioBreeding (BBDP) rat. Gimap5 is a member of seven related genes located within 150 Kb on rat chromosome 4. Congenic DR.(lyp/lyp) rats, where BBDP lyp was introgressed onto the diabetes-resistant BBDR background (BBDR.BBDP.(lyp/lyp)), all develop diabetes between 46 and 81 days of age (mean +/- SE, 61 +/- 1), whereas DR.(lyp/+) and DR.(+/+) rats are nonlymphopenic and diabetes resistant. In an intercross between F1(BBDP x F344) rats, we identified a rat with a recombination event on chromosome 4, allowing us to fix 33 Mb of F344 between D4Rat253 and D4Rhw6 in the congenic DR.lyp rat line. Gimap1 and Gimap5 were the only members of the Gimap family remaining homozygous for the BBDP allele. Offspring homozygous for the F344 allele (f/f) between D4Rat253 and D4Rhw6 were lymphopenic (85 of 85, 100%) but did not develop diabetes (0 of 85). During rescue of the recombination, 102 of 163 (63%) rats heterozygous (b/f) for the recombination developed diabetes between 52 and 222 days of age (88 +/- 3). Our data demonstrate that introgression of a 33-Mb region of the F344 genome, proximal to the mutated Gimap5 gene, renders the rat diabetes resistant despite being lymphopenic. Spontaneous diabetes in the BB rat may therefore be controlled, in part, by a diabetogenic factor(s), perhaps unrelated to the Gimap5 mutation on rat chromosome 4.

DR.lyp/lyp bone marrow maintains lymphopenia and promotes diabetes in lyp/lyp but not in +/+ recipient DR.lyp BB rats

Lymphopenia is due to a frameshift mutation in Gimap5 on rat chromosome 4 and is linked to type 1 diabetes in the diabetes prone (DP) BB rat. The hypothesis that bone marrow derived cells confer the lymphopenia phenotype was tested by reciprocal bone marrow transplantation in 40-day-old lethally irradiated diabetes resistant (DR) congenic DR.lyp/lyp (lymphopenia and diabetes) and DR.+/+ (no lymphopenia and no diabetes) rats. In two independent series of transplants, all DR.lyp/lyp rats (n=5 and 4) receiving DR.lyp/lyp bone marrow retained lymphopenia and developed insulitis (5/5 and 4/4) as well as diabetes in some (2/5 and 3/4). Both DR.+/+ and DR.lyp/lyp rats receiving DR.+/+ bone marrow cells as well as DR.+/+ rats receiving DR.lyp/lyp bone marrow cells showed no lymphopenia or diabetes. In accordance with earlier studies in non-congenic BB rats, the DR.+/+ rats receiving DR.lyp/lyp bone marrow cells recapitulated an intermediary phenotype rather than the +/+ or lyp/lyp phenotypes. Our data demonstrate that BBDP rat lymphopenia and diabetes are transferred by bone marrow transplantation to syngeneic DR.lyp/lyp but not DR.+/+ recipients. The intermediary recapitulation of DR.lyp/lyp T cells in recipient DR.+/-/+/- rats suggests that radiation resistant +/-/+/- T cells, the Gimap5 mutation in bone marrow cells, or both may not support the development of lymphopenia.

Control of homeostatic proliferation by regulatory T cells

Homeostatic proliferation of T cells leads to the generation of effector/memory cells, which have the potential to cause harm to the host. The role of Tregs in the control of homeostatic proliferation is unclear. In this study we utilized mice that either harbor or lack Tregs as recipients of monoclonal or polyclonal T cells. We observed that while Tregs completely prevented cell division of T cells displaying low affinity for self ligands, they had a less marked, albeit significant, effect on cell cycle entry of T cells displaying higher affinity. The presence of Tregs resulted in a lower accumulation of T cells, enhanced apoptosis, and impaired differentiation to a cytokine-producing state. We conclude that Tregs play a major role in the control of homeostatic proliferation.

Effects of polyinosinic-polycytidylic acid and adoptive transfer of immune cells in the Lew.1AR1-iddm rat and in its coisogenic LEW.1AR1 background strain

The importance of the cellular immune system for the development of T1DM in the LEW.1AR1-iddm rat was investigated by use of polyinosinic-polycytidylic acid (Poly I:C) and by adoptive transfer of concanavalin A (Con A) activated lymphocytes from diabetic LEW.1AR1-iddm rats and the coisogenic LEW.AR1 background strain. Poly I:C treatment induced diabetes, characterized morphologically by a diffuse infiltration of the pancreas, in up to 20% of the animals of the coisogenic LEW.1AR1 background strain. It did not increase the diabetes incidence of 30% of the LEW.1AR1-iddm strain. In contrast Poly I:C treatment induced diabetes in up to 80% of the animals of the Mhc congenic LEW.1WR1 strain. Adoptive transfer of lymphocytes activated by the T-cell mitogen Con A from diabetic donors doubled the incidence of diabetes, characterized morphologically by a focal insulitis, in diabetes prone LEW.1AR1-iddm recipients. In contrast, animals of the LEW.1AR1 background strain did not develop diabetes after adoptive transfer. Moreover, adoptive transfer of Con A activated lymphocytes from LEW.1AR1 rats to LEW.1AR1-iddm rats with 30 or 60% diabetes incidence, significantly decreased the incidence of diabetes in LEW.1AR1-iddm rats with 60% diabetes incidence. The results show that autoreactive lymphocytes induce beta cell destruction in the LEW.1AR1-iddm rat, while the LEW.AR1 background strain apparently contains regulatory potential, which is able to counteract the autoimmune response.

Aberrancies in the differentiation and maturation of dendritic cells from bone-marrow precursors are linked to various genes on chromosome 4 and other chromosomes of the BB-DP rat

BB-Diabetes Prone (BB-DP) rats, a model for endocrine autoimmune diseases, are severely lymphopenic, especially lacking ART2+ regulatory T cells. BB-Diabetes Resistant (DR) rats are not lymphopenic and do not develop autoimmunity. BB-DP and BB-DR rats only differ at the lymphopenia (lyp) gene (iddm2) on chromosome 4. Since BB-DP rats also show aberrancies in the differentiation of dendritic cells (DC) from bone-marrow precursors, we tested the hypothesis that F344 rats congenic for a BB-DP chromosome 4 region (42.5-93.6Mb; including the lyp gene, but also iddm4) display an in vitro DC differentiation different from normal F344 rats. Here we show that the 42.5-93.6Mb BB-DP chromosome 4 region is linked to an increased DC precursor apoptosis, a low MHC class II expression, a reduced IL-10 production and a reduced T cell stimulatory capacity of DC. From our previous report on DC differentiation defects in BB rats (only differing in iddm2) and the present report, we deduce that the abnormal apoptosis and low MHC class II expression is linked to iddm2. The reduced T cell stimulatory capacity is linked to other genes on chromosome 4 (candidate gene: iddm4). The reduced IL-10 production has a complex linkage pattern.

Involvement of eotaxin, eosinophils, and pancreatic predisposition in development of type 1 diabetes mellitus in the BioBreeding rat

Allergy and autoimmunity are both examples of deregulated immunity characterized by inflammation and injury of targeted tissues that have until recently been considered disparate disease processes. However, recent findings have implicated mast cells, in coordination with granulocytes and other immune effector cells, in the pathology of these two disorders. The BioBreeding (BB) DRlyp/lyp rat develops an autoimmune insulin-dependent diabetes similar to human type 1 diabetes mellitus (T1DM), whereas the BBDR+/+ rat does not. To better understand immune processes during development of T1DM, gene expression profiling at day (d) 40 (before insulitis) and d65 (before disease onset) was conducted on pancreatic lymph nodes of DRlyp/lyp, DR+/+, and Wistar-Furth (WF) rats. The eosinophil-recruiting chemokine, eotaxin, and the high-affinity IgE receptor (FcepsilonRI) were up-regulated >5-fold in d65 DRlyp/lyp vs d65 DR+/+ pancreatic lymph nodes by microarray (p < 0.05) and quantitative RT-PCR studies (p < 0.05). DR+/+, WF, and d40 DRlyp/lyp animals possessed normal pancreatic histology; however, d65 DRlyp/lyp animals possessed eosinophilic insulitis. Therefore, immunohistochemistry for pancreatic eotaxin expression was conducted, revealing positive staining of d65 DRlyp/lyp islets. Islets of d65 DR+/+ rats also stained positively, consistent with underlying diabetic predisposition in the BB lineage, whereas WF islets did not. Other differentially expressed transcripts included those associated with eosinophils, mast cells, and lymphocytes. These data support an important role for these inflammatory mediators in BB rat T1DM and suggest that the lymphopenia due to the Ian5/(lyp) mutation may result in a deregulation of cells involved in insulitis and beta cell destruction.

Transgenic rescue demonstrates involvement of the Ian5 gene in T cell development in the rat

A single point mutation in a novel immune-associated nucleotide gene 5 ( Ian5) coincides with severe T cell lymphopenia in BB rats. We used a transgenic rescue approach in lymphopenic BB-derived congenic F344. lyp/ lyp rats to determine whether this mutation is responsible for lymphopenia and to establish the functional importance of this novel gene. A 150-kb P1 artificial chromosome (PAC) transgene harboring a wild-type allele of the rat Ian5 gene restored Ian5 transcript and protein levels, completely rescuing the T cell lymphopenia in the F344. lyp/ lyp rats. This successful complementation provides direct functional evidence that the Ian5 gene product is essential for maintaining normal T cell levels. It also demonstrates that transgenic rescue in the rat is a practical and definitive method for revealing the function of a novel gene.

Genetic dissection of lymphopenia from autoimmunity by introgression of mutated Ian5 gene onto the F344 rat

Peripheral T cell lymphopenia (lyp) in the BioBreeding (BB) rat is linked to a frameshift mutation in Ian5, a member of the Immune Associated Nucleotide (Ian) gene family on rat chromosome 4. This lymphopenia leads to type 1 (insulin-dependent) diabetes mellitus (T1DM) at rates up to 100% when combined with the BB rat MHC RT1 u/u genotype. In order, to better study the lymphopenia phenotype without possible confounding effects of diabetes or other autoimmune disease, we generated congenic F344.lyp rats by introgression of lyp on diabetes-resistant MHC RT1 lv1/lv1 F344 rats. Analysis of thymic CD4 and CD8 T lymphocytes revealed no difference in the percentage of CD4⁻CD8⁺and CD4⁺CD8⁻subsets in lyp/lyp compared to +/+ F344 rats. The same subsets was however dramatically reduced in blood (P=0.005), spleen (P=0.019) and mesenteric lymph nodes (MLN) (P<0.0001). Compared to F344 +/+ rats double positive CD4⁺CD8⁺T cells were increased only in lyp/lyp spleen (P=0.034) while double negative CD4⁻CD8⁻were increased in thymus (P=0.033), spleen (P=0.012), MLN (P<0.0001), and peripheral blood (P<0.0001). There were no signs of inflammatory lesions in organs and tissues in F344.lyp/lyp rats examined at 120 days of age or older. We thus conclude that the lymphopenia phenotype was reconstituted by introgression of lyp on to F344 rats without subsequent development of organ-specific autoimmunity. The congenic F344.lyp rat should prove useful to dissect the mechanisms by which the Ian5 frameshift mutation affects T cell selection, differentiation and maturation without organ-specific autoimmunity.

New autoimmune genes and the pathogenesis of type 1 diabetes

Type 1 diabetes is an autoimmune disease with a complex polygenic inheritance. Until recently, only three susceptibility genes had been reproducibly identified, namely HLA, INS-VNTR, and CTLA4. During the past 7 years, a number of new putative susceptibility genes have been isolated from both human and animal models of the disease. We present eight genes implicated in type 1 diabetes etiology and discuss them in relation to the pathogenesis of the disease: VDR, IL6, IL12B, AIRE, FOXP3, B2m, Cblb, and Lyp/Ian4l1.

The iddm4 locus segregates with diabetes susceptibility in congenic WF.iddm4 rats

Viral antibody-free BBDR and WF rats never develop spontaneous diabetes. BBDR rats, however, develop autoimmune diabetes after perturbation of the immune system, e.g., by viral infection. We previously identified a disease-susceptibility locus in the BBDR rat, iddm4, which is associated with the development of autoimmune diabetes after treatment with polyinosinic:polycytidylic acid and an antibody that depletes ART2(+) regulatory cells. We have now developed lines of congenic WF.iddm4 rats and report that in an intercross of N5 generation WF.iddm4 rats, approximately 70% of animals either homozygous or heterozygous for the BBDR origin allele of iddm4 became hyperglycemic after treatment to induce diabetes. Fewer than 20% of rats expressing the WF origin allele of iddm4 became diabetic. Testing the progeny of various recombinant N5 WF.iddm4 congenic rats for susceptibility to diabetes suggests that iddm4 is centered on a small segment of chromosome 4 bounded by the proximal marker D4Rat135 and the distal marker D4Got51, an interval of <2.8 cM. The allele at iddm4 has 79% sensitivity and 80% specificity in prediction of diabetes in rats that are segregating for this locus. These characteristics suggest that iddm4 is one of the most powerful non-major histocompatibility complex determinants of susceptibility to autoimmune diabetes described to date.

Thymectomy and radiation-induced type 1 diabetes in nonlymphopenic BB rats

Spontaneous type 1 diabetes in BB rats is dependent on the RT1(u) MHC haplotype and homozygosity for an allele at the Lyp locus, which is responsible for a peripheral T-lymphopenia. Genetic studies have shown that there are other, as yet unidentified, genetic loci contributing to diabetes susceptibility in this strain. BB rats carrying wild-type Lyp alleles are not lymphopenic and are resistant to spontaneous diabetes (DR). Here we show that thymectomy and exposure to one sublethal dose of gamma-irradiation (TX-R) at 4 weeks of age result in the rapid development of insulitis followed by diabetes in 100% of DR rats. Administration of CD4(+)45RC(-) T-cells from unmanipulated, syngeneic donors immediately after irradiation prevents the disease. Splenic T-cells from TX-R-induced diabetic animals adoptively transfer type 1 diabetes to T-deficient recipients. ACI, WF, WAG, BN, LEW, PVG, and PVG.RT1(u) strains are resistant to TX-R-induced insulitis/diabetes. Genetic analyses revealed linkage between regions on chromosomes 1, 3, 4, 6, 9, and 16, and TX-R-induced type 1 diabetes in a cohort of nonlymphopenic F(2) (Wistar Furth x BBDP) animals. This novel model of TX-R-induced diabetes in nonlymphopenic BB rats can be used to identify environmental and cellular factors that are responsible for the initiation of antipancreatic autoimmunity.

The diabetes-prone BB rat carries a frameshift mutation in Ian4, a positional candidate of Iddm1

Diabetes-prone (DP) BB rats spontaneously develop insulin-dependent diabetes resembling human type 1 diabetes. They also exhibit lifelong T-cell lymphopenia. Functional and genetic data support the hypothesis that the gene responsible for the lymphopenia, Lyp, is also a diabetes susceptibility gene, named Iddm1. We constructed a 550-kb P1-derived artificial chromosome contig of the region. Here, we present a corrected genetic map reducing the genetic interval to 0.2 cM and the physical interval to 150-290 kb. A total of 13 genes and six GenomeScan models are assigned to the homologous human DNA segment on HSA7q36.1, 8 of which belong to the family of immune-associated nucleotides (Ian genes). Two of these are orthologous to mouse Ian1 and -4, both excellent candidates for Iddm1. In normal rats, they are expressed in the thymus and T-cell regions of the spleen. In the thymus of lymphopenic rats, Ian1 exhibits wild-type expression patterns, whereas Ian4 expression is reduced. Mutational screening of their coding sequences revealed a frameshift mutation in Ian4 among lymphopenic rats. The mutation results in a truncated protein in which the COOH-terminal 215 amino acids-including the anchor localizing the protein to the outer mitochondrial membrane-are replaced by 19 other amino acids. We propose that Ian4 is identical to Iddm1.

The antibody response to bacteriophage is linked to the lymphopenia gene in congenic BioBreeding rats

Congenic BioBreeding (BB) rats, homozygous for the autosomal lymphopenia (Lyp) gene (Lyp/Lyp), heterozygous (Lyp/+), or wild-type (+/+), were immunized with the T cell-dependent bacteriophage PhiX174 to determine effects of Lyp on primary and secondary antibody responses. The primary PhiX174 antibody response did not differ between the three different genotypes. In contrast, the secondary immune response, expressed as the peak neutralizing titer, was markedly reduced in Lyp/Lyp (9.9+/-3.2; mean value+/-S.E.M. for seven rats) compared to both Lyp/+ (51+/-12; n=13; P=0.006) and +/+ (100+/-20; n=7; P=0.004) BB rats. We suggest that the secondary antibody response to the T cell-dependent neoantigen PhiX174 is linked in a recessive manner to genetic factor(s) in the Lyp gene region.

Development and function of diabetogenic T-cells in B-cell-deficient nonobese diabetic mice

Insulin-dependent diabetes (type 1 diabetes) in the NOD mouse is a T-cell-mediated autoimmune disease. However, B-cells may also play a critical role in disease pathogenesis, as genetically B-cell-deficient NOD mice (NOD.microMT) have been shown to be protected from type 1 diabetes and to display reduced responses to certain islet autoantigens. To examine the requirements for B-cells in the development of type 1 diabetes, we generated a B-cell-naive T-cell repertoire by transplantation of NOD fetal thymuses (FTs) into NOD.scid recipients. Surprisingly, these FT-derived NOD T-cells were diabetogenic in 36% of NOD.scid recipients, despite the absence of B-cells. In addition, T-cells isolated from NOD.microMT mice were diabetogenic in 22% of NOD.scid recipients. Together, these results indicate that B-cells are not an absolute requirement for the generation or effector function of an islet-reactive T-cell repertoire in NOD mice. We suggest that conditions favoring rapid lymphocyte expansion can reveal autoreactive T-cell activity and precipitate disease in genetically susceptible individuals.

The identification of a novel T cell activation state controlled by a diabetogenic gene

The cyclin-dependent kinase inhibitor p27(kip) regulates the cell cycle at the G(1)-S phase restriction point. S phase entry and cell cycle commitment in peripheral T cells requires p27(kip) degradation, normally initiated by the receipt of costimulatory signals such as those provided by B7.1 or IL-2. We have previously reported that T cells from BioBreeding (BB)-diabetes-prone (DP) rats exhibit decreased costimulatory requirements for activation and cell cycle entry. In the present study, we find that peripheral T cell subsets from BB-DP rats demonstrate activation-like characteristics, including significantly reduced levels of p27(kip) as well as increased levels of proliferating cell nuclear Ag (PCNA). Since our previous studies have established that expression of extracellular activation markers are relatively low in unmanipulated peripheral BB-DP T cells; this p27(low) PCNA(high) phenotype represents a novel activation state. Analyses of T cell subsets from congenic rats demonstrate that this phenotype segregates with the lyp diabetogenic locus and that the p27(low) PCNA(high) phenotype is T cell specific. This p27(low) PCNA(high) phenotype is not seen in medullary thymocytes, but appears abruptly in the recent thymic emigrant population, suggesting that the lyp locus does not act directly on cell cycle regulators but rather alters the interaction between T cells and the peripheral environment. These results provide a biochemical basis for costimulation-independent activation and suggest a mechanism whereby a diabetes susceptibility gene contributes to disease development.

A sequence-ready PAC contig of a 550-kb region on rat chromosome 4 including the diabetes susceptibility gene Lyp

The Lyp locus controls diabetes development in rats. The diabetogenic allele in diabetes-prone BB rats is responsible for T cell lymphopenia characterized by the absence of regulatory T cells. We present refined genetic and radiation hybrid maps of the Lyp region on rat chromosome 4, a single 800-kb rat yeast artificial chromosome and a rat P1-derived artificial chromosome (PAC) contig corresponding to approximately 550 kb, both encompassing the entire candidate region. The contig, consisting of 48 PACs, gives 3- to 12-fold coverage. Genetic, radiation hybrid, and physical data were all in agreement and supported the same marker order. Nine genes and ESTs were identified in the contig in addition to a rat EST from the University of Iowa rat EST database-all possible candidate genes for Lyp. Alignment of our rat PAC contig with sequenced human PAC/BAC contigs confirms the position within the region of 3 of the 10 candidates and identifies an additional 8 genes/ESTs as candidates. These data will facilitate identification of Lyp.

Elevated apoptosis of peripheral T lymphocytes in diabetic BB rats

Thymocytes and peripheral lymphocytes of BioBreeding (BB) diabetes-prone (BBDP) and diabetes-resistant (BBDR) rat were analysed by fluorescence-activated cell sorter (FACS). The number of CD4- CD8-, CD4+ CD8-, CD4- CD8+ and CD4+ CD8+ subsets was not different between BBDP and BBDR rat thymocytes, whereas spleen and lymph nodes in BBDP rats undergo severe T-cell lymphopenia. Notably, mature CD4- CD8+ [T-cell receptor (TCR)-alphabeta+ and CD5+] cells are certainly present in the BBDP rat thymus, unlike some previous reports, suggesting that the differentiation of CD4- CD8+ from CD4+ CD8+ cells occurs normally in the BBDP rat thymus. As a cause of peripheral T-cell lymphopenia we suspected apoptosis of recent thymic emigrants. By FACS analysis with fluorescein isothiocyanate-labelled annexin V, elevated apoptosis was evident in BBDP rat peripheral lymphocytes. Furthermore, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL) staining in BBDP rat splenic sections revealed that a number of TUNEL-positive cells were observed in the T-lymphocyte-rich area. From these results, we postulate that an abnormally elevated apoptosis of peripheral T lymphocytes, but not impaired thymocyte differentiation, is a cause of the peripheral T-cell lymphopenia in BBDP rats.

A diabetogenic gene prevents T cells from receiving costimulatory signals

T cell fate following antigen encounter is determined by several intracellular signals generated by the interaction of the T cell with an antigen-presenting cell. In the periphery activation requires T cell receptor signaling (signal one) in combination with costimulatory signals (signal two), usually provided through the cognate interaction of CD28 and B7 molecules. Provision of signal one alone to purified murine peripheral T cells in vitro induces apoptosis or anergy rather than promoting activation. These T cells can be rescued from apoptosis if they are provided with costimulation supplied, for example, by engaging the CD28 co-receptor with an anti-CD28 monoclonal antibody or by adding an exogenous source of interleukin-2. However, a majority of peripheral T cells from autoimmune, diabetes-prone Biobreeding (BB) rats exhibited different responses to these stimuli. T cells from these rats could not be rescued from apoptosis by costimulation. This was not due to the inability of BB-DP T cells to upregulate CD28 and the IL-2 receptor in response to TCR crosslinking. The failure of these costimulatory interactions to rescue BB-DP T cells segregated with the diabetes-susceptibility gene iddm1. Iddm1 in the rat causes peripheral T cell lymphopenia, which is associated with a dramatically shortened peripheral T cell life span. Our results indicate that a diabetogenic gene may contribute to autoimmunity by negating costimulatory signals important for the survival of long-lived peripheral T cells.

Recapitulation of Normal and Abnormal BioBreeding Rat T Cell Development in Adult Thymus Organ Culture

Congenitally lymphopenic diabetes-prone (DP) BioBreeding (BB) rats develop spontaneous T cell-dependent autoimmunity. Coisogenic diabetes-resistant (DR) BB rats are not lymphopenic and are free of spontaneous autoimmune disease, but become diabetic in response to depletion of RT6+ T cells. The basis for the predisposition to autoimmunity in BB rats is unknown. Abnormal T cell development in DP-BB rats can be detected intrathymically, and thymocytes from DR-BB rats adoptively transfer diabetes. The mechanisms underlying these T cell developmental abnormalities are not known. To study these processes, we established adult thymus organ cultures (ATOC). We report that cultured DR- and DP-BB rat thymi generate mature CD4 and CD8 single-positive cells with up-regulated TCRs. DR-BB rat cultures also generate T cells that express RT6. In contrast, DP-BB rat cultures generate fewer CD4+, CD8+, and RT6+ T cells. Analysis of the cells obtained from ATOC suggested that the failure of cultured DP-BB rat thymi to generate T cells with a mature phenotype is due in part to an increased rate of apoptosis. Consistent with this inference, we observed that addition of the general caspase inhibitor Z-VAD-FMK substantially increases the number of both mature and immature T cells produced by DP-BB rat ATOC. We conclude that cultured DR-BB and DP-BB rat thymi, respectively, recapitulate the normal and abnormal T cell developmental kinetics and phenotypes observed in these animals in vivo. Such cultures should facilitate identification of the underlying pathological processes that lead to immune dysfunction and autoimmunity in BB rats.

High Frequency Apoptosis of Recent Thymic Emigrants in the Liver of Lymphopenic Diabetes-Prone BioBreeding Rats

Diabetes-prone (DP) BioBreeding (BB) rats develop spontaneous autoimmune diabetes. DP-BB thymocyte export is reduced, and most thymic emigrants disappear rapidly from peripheral lymphoid tissues. DP-BB rats are consequently lymphopenic and circulate severely reduced numbers of T cells. Peripheral T cells present are phenotypically immature (Thy1+) and appear activated. We hypothesized that DP-BB recent thymic emigrants have a shortened life span and disappear by apoptosis. The percentage of T cells with an αβTCRlowB220+CD4−CD8− phenotype was increased in DP peripheral lymphoid tissues when compared with normal, nonlymphopenic diabetes-resistant (DR) BB rat tissues. There was no evidence of DNA fragmentation in freshly isolated DP- or DR-BB rat cells, but, after 24 h of culture, a higher proportion of DP- than DR-BB splenic T cells underwent apoptosis. We then tested the hypothesis that BB rat T cells with the αβTCRlowB220+CD4−CD8− phenotype accumulate and undergo apoptosis in the liver. Such cells were observed undergoing apoptosis in both DP- and DR-BB rats, but comprised ∼80% of intrahepatic T cells in DP vs ∼20% in DR-BB rats. Most αβTCRlowB220+CD4−CD8− cells in the liver were also Thy1+. The data suggest that T cell apoptosis in the DP-BB rat is underway in peripheral lymphoid tissues and is completed in the liver. Increased intrahepatic apoptosis of recent thymic emigrants appears in part responsible for lymphopenia in DP-BB rats and the concomitant predisposition of these animals to autoimmunity.

Segregation of autoimmune type 1 diabetes in a cross between diabetic BB and brown Norway rats

Diabetes-prone DP-BB rats spontaneously develop insulin-dependent diabetes mellitus resembling type 1 diabetes mellitus in man. Expression of T cell lymphopenia and presence of at least one class II major histocompatibility complex (MHC) RT1u haplotype are required for development of diabetes. Diabetes segregation was studied in lymphopenic backcross (BC) offspring from a cross between male DP-BB/HRI and female BN/Mol rats. Diabetes occurred in 75% of BC rats with genotype RT1u/u and in 18% of those being RT1n/u in genotype. The latter developed diabetes significantly later than MHC homozygotes and parental DP-BBs. Our data further point to the existence of additional genes of minor importance for development of IDDM. One of these seemed to be positioned on the X chromosome. The recently published linkage to chromosome 18 could not be confirmed however. Finally, the BN-derived non-albino allele of the C gene was associated with higher diabetes incidence. This points to the existence of minor susceptibility genes in other strains of rats.

Abnormalities in the export and fate of recent thymic emigrants in diabetes-prone BB/W rats

Abnormalities in postthymic T cell development in the BB/W rat model of autoimmune insulin-dependent diabetes mellitus (IDDM) result in part from a lymphopenia (lyp) gene defect. To better characterize these abnormalities, the phenotypes of T cells from diabetes-prone (DP) and diabetes-resistant (DR) coisogenic rats were analyzed by multiparameter flow immunocytometry (FCM). Marked decreases in the numbers of Thy1- RT6+ T cells, most of which are CD8+, were documented in DP rats by live-gating. Conversely, an approximately 3-fold increase was observed in the percentage of Thy1+ RT6- T cells, which normally serve as the precursors of both Thy1- RT6+ and Thy1- RT6- T cell subsets in rats. These results suggested that, at a minimum, an arrest in maturation of the Thy1+ precursors of RT6+ T cells occurs postthymically in DP rats. To determine more precisely the stage(s) in T cell development at which lymphopenia occurs, the export and fate of recent thymic emigrants (RTE's) and their immediate descendants in DP rats was traced after intrathymic (i.t.) labelling with fluorescein isothiocyanate (FITC). The results showed that in DP, as compared with DR, rats: 1) 5-fold fewer RTE's are exported from the thymus per 24 hr; 2) more than 80% of the RTE's are CD4+; 3) most of the immediate descendants of RTE's disappear from the peripheral lymphoid tissues within one week after export from the thymus; and 4) few of the descendants of the RTE's that do survive differentiate into RT6+ T cells. Staining with propidium iodide revealed that a significantly higher proportion of Thy1+ T cells in DP than in DR rats are in cycle (S/G2/M), thereby accounting for their disproportionately high numbers relative to RTE's. These results indicate that, in addition to defective thymic export, most of the immediate descendants of RTE's in DP rats undergo non-productive proliferation and death at the time (3-7 days postthymic) at which their counterparts in DR rats differentiate into Thy1- RT6+ T cells. The resulting deficiency of immunoregulatory T cells, acting in concert with defective intrathymic selection of effector T cell precursors, appears to conspire to markedly enhance the predisposition of DP rats to autoimmunity.

Thyroiditis in the BB rat is associated with lymphopenia but occurs independently of diabetes

The spontaneously diabetic BB rat is an excellent and well studied model for human insulin-dependent diabetes (IDDM), sharing many important features with the human disease. Similarities include an equal frequency of IDDM in males and females, production of antibodies against pancreatic cell antigens, and an MHC disease association. In addition, the BB rat shares with human IDDM patients an increased frequency of autoantibodies against the parietal cells of the stomach and colloid cells of the thyroid gland. Here we investigate the genetic basis of thyroiditis in the BB rat. Based on crosses between BB, Lewis and Fischer rats, we show that two susceptibility factors for diabetes--the lymphopenia trait present in diabetes prone BB rats and the MHC--also appear to be risk factors for thyroiditis. However, the nature of the susceptibility was different for the two autoimmune diseases, with lymphopenia being absolutely required for diabetes although it only conferred increased risk for thyroiditis. Also, in contrast to IDDM, the MHC conferred dominant susceptibility to thyroiditis. Despite these shared risk factors, diabetes per se did not show significant correlation with thyroiditis.

T cells from BB-DP rats show a unique cytokine mRNA profile associated with the IDDM1 susceptibility gene, Lyp

Diabetes prone biobreeding rats display several abnormalities in T cell numbers, T cell function and T cell surface phenotype which are associated with the onset of spontaneous disease. One of the most pronounced abnormalities in these animals is a marked T cell lymphopenia which is evident in both CD4+ and CD8+ peripheral T cell subsets. To gain a better understanding as to the nature of T cell responses in these animals, we have utilized RT-PCR to analyze the cytokine mRNA profiles of mitogen activated peripheral T cells derived from lymphopenic and non-lymphopenic animals. Our results suggest that inheritance of the lymphopenia gene, Lyp, is associated with a unique cytokine profile most similar to that previously described for mouse medullary thymocytes. In addition, cell surface staining of peripheral T cells from diabetes prone animals revealed a high frequency of Thyl+ cells, which is characteristic of both thymocytes and recent thymic emigrants. Following thymectomy, T cell responsiveness to a number of different stimuli is greatly reduced on a cell for cell basis as is the absolute number of surviving T cells. Taken collectively, our results suggest that the majority of the peripheral T cell pool in these diabetic prone rats consists of short lived, recent thymic emigrants which most likely also contain the effector cells required for initiation of diabetes.

Thymic epithelial defects and predisposition to autoimmune disease in BB rats

We report an association between thymic epithelial defects and predisposition to autoimmunity. Diabetes-prone (DP) BB rats develop spontaneous hyperglycemia and are deficient in T cell subsets expressing the RT6 alloantigen. Diabetes resistant (DR) BB rats become diabetic if depleted of RT6+ T cells. The inciting immune system defects are unknown. We made the following observations: 1) Regions of thymic cortex and medulla devoid of thymic epithelium exist in DP-BB, DR-BB, and Lewis rats, all of which are susceptible to autoimmune disorders. Such defects were absent in eight normal rat strains. 2) Thymic epithelial defects are absent at birth, but present in BB rats at 4 weeks of age. 3) The genetic predisposition to thymic epithelial defects is an autosomal dominant trait. 4) The observation of thymic defects in (DP x WF)F1 rats led to the prediction that such animals, which never develop spontaneous autoimmunity, might be susceptible to its induction. Following depletion of RT6+ T cells we observed diabetes in 91%, and thyroiditis in 43%, of treated F1 animals (n = 23). Pancreatic insulitis was uniformly present. Because thymic epithelium participates in the positive and negative selection of developing thymocytes, we propose that thymic epithelial defects may play an important role in the predisposition of BB rats to autoimmunity.

Decreased weight gain in BB rats before the clinical onset of insulin-dependent diabetes

Inbred specific pathogen-free diabetes-prone (DP) and diabetes-resistant (DR) BB rats were crossed to produce F1 and intercrossed to produce F2 rats. Diabetes segregates in these crosses as a recessive trait on rat chromosome 4. The weight gain of genetically diabetes-prone rats born to F1 healthy parents was studied to avoid effects of maternal diabetes. The weight gain of the F2 rats was initially not different from the F1 parents. The F2 rats later developing diabetes grew in parallel with their non-affected siblings up until the last 9 days before onset. During these 9 days they showed a decreased weight gain compared to their healthy litter-mates regardless of age. We conclude that decreased weight gain precedes the abrupt clinical onset of diabetes in BB rats and that it may be due to processes associated with the selective loss of beta cells.

Diabetes mellitus induced inhibition of glucosaminyl N-deacetylase: effect of short-term blood glucose control in diabetic rats

Inhibition of glucosaminyl N-deacetylase activity, a key enzyme in heparan sulphate sulphation, may be involved in the development of late diabetic vascular complications. We examined the effect of short- and long-term metabolic control on N-deacetylase activity in streptozotocin diabetic H and U rats. Spontaneously diabetic BB rats were included in parts of the study. Over a 3-week period blood glucose was maintained at predetermined levels (6-10 mmol/l or 10-20 mmol/l) by insulin treatment and then during the final 2 days rapidly reversed in half of each group. In the U rats, the hepatic N-deacetylase activity significantly decreased by 10-15% following short- and long-term poor metabolic control and the inhibition was entirely reversed by short-term good control. In the H rats a similar, not significant, effect was seen. BB rats in long-term poor control showed a 10% reduction in hepatic N-deacetylase activity (p = 0.003). Glomerular N-deacetylase activity was reduced in U rats after long-term poor control (p = 0.004) but not in H and BB rats. There was an overall correlation between urinary albumin excretion and glomerular N-deacetylase activity (r = -0.60, p < 0.0001). We conclude that diabetes-induced inhibition of hepatic N-deacetylase is not restricted to the streptozotocin diabetic model, and that short-term blood glucose control is of major importance. Genetic factors and tissue specificity influence the vulnerability of the enzyme. Finally, the study suggests an association between N-deacetylase activity and urinary albumin excretion.

BB-DR/Edinburgh: a lymphopenic, non-diabetic subline of BB rats

Diabetes-prone (DP) and diabetes-resistant (DR) sublines of the BB rat have been established in Edinburgh, U.K., separately from other existing colonies. In an examination of the lymphoid status of the two lines, BB-DP/Ed and BB-DR/Ed, it has been found that both lines have very low T-cell numbers, depressed B-lymphocyte numbers and a complete absence of peripheral CD8+ T cells, all features characteristic of the previously described genetic lymphopenia lesion. It was also noted that the peripheral T cells of both BB/Ed lines were larger than normal. The DP/Ed and DR/Ed lines were indistinguishable in all these respects, and furthermore, they were both shown to type as RT1u at the major histocompatibility complex (MHC). The genetic combination of lymphopenia and RT1u without expression of diabetes is not present in other extant BB lines and makes BB-DR/Ed a uniquely useful control strain for BB rat studies as well as a valuable genetic resource for the further genetic analysis of diabetes susceptibility in rats.

Protection from BB rat diabetes by the platelet-activating factor inhibitor BN50730

The platelet-activating factor inhibitor BN50730, a hetrazepine, was injected intraperitoneally daily from 30 days of age into diabetes-prone BB rats. While 96% (22/23) Tween 80 injected control rats developed diabetes, 0.05 mg/kg BN50730 decreased the frequency to 72% (17/24; n.s.) and 0.5 mg/kg to 56% (14/25; p < 0.01). Mean onset age in controls was 81 +/- 9 days (mean +/- SD), but BN50730 delayed onset to 87 +/- 15 days in the low and 93 +/- 12. days (p < 0.01) in high dose rats. The relative degree of insulitis was reduced in both low (p < 0.01) and high (p < 0.05) dose treated groups. Serum insulin in young prediabetic controls decreased from 84 +/- 34 microU/ml to 38 +/- 20 in the 22 rats developing diabetes (p < 0.001). Serum insulin in BN50730-protected compared to unprotected rats was 114 +/- 49 and 32 +/- 22 (p < 0.001) in the low, and 91 +/- 46 and 21 +/- 15 (p < 0.001) microU/ml in the high dose group, respectively. Increased serum insulin correlated with preserved islet beta cells and decreased insulitis. Treatment did not affect thyroiditis. Thus, platelet-activating factor may be involved in insulitis pathogenesis and platelet-activating factor inhibitors may decrease autoimmune beta cell destruction.

Genetic dissection of autoimmune type I diabetes in the BB rat

The BB rat is among the best models of insulin-dependent diabetes mellitus--with onset and pathogenesis closely resembling the human disease. One unusual feature is a severe T-cell lymphopenia, which appears to be inherited as a recessive trait controlled by a single gene, Lyp. Based on genetic analysis of several crosses, we show that development of diabetes involves at least three genes: Lyp, which is tightly linked to the neuropeptide Y (Npy) gene on chromosome 4, a gene linked to the major histocompatibility complex (MHC) on chromosome 20, and a third unmapped gene for which the Fischer rat strain carries an allele conferring resistance.