Genetic control of parasite clearance leads to resistance to Plasmodium berghei ANKA infection and confers immunity.

Unprecedented cure after infection with the lethal Plasmodium berghei ANKA was observed in an F2 progeny generated by intercrossing the wild-derived WLA and the laboratory C57BL/6 mouse strains. Resistant mice were able to clear parasitaemia and establish immunity. The observed resistance was disclosed as a combinatorial effect of genetic factors derived from the two parental strains. Genetic mapping of survival time showed that the WLA allele at a locus on chromosome 1 (colocalizing with Berghei resistance 1 (Berr1), a locus associated with resistance to experimental cerebral malaria) increases the probability to resist early death. Also, the C57Bl/6 allele at a novel locus on chromosome 9 (Berr3) confers overall resistance to this lethal Plasmodium infection. This report underlines the value of using wild-derived mouse strains to identify novel genetic factors in the aetiology of disease phenotypes, and provides a unique model for studying parasite clearance and immunity associated with malaria.

Low rate of proliferation in immature thymocytes of the non-obese diabetic mouse maps to the Idd6 diabetes susceptibility region.

AIMS/HYPOTHESIS: The non-obese diabetic (NOD) mouse spontaneously develops T-cell-dependent autoimmune diabetes. This mouse strain has a number of immune dysfunctions related to T-cell development but so far there are no available data on the proliferation of NOD immature thymocytes. We therefore studied the thymocyte proliferation in the NOD mouse in discrete stages of T-cell development. METHODS: We depleted thymocytes in vivo and analysed thymocyte proliferation during the thymus recovery from depletion. We used co-segregation analysis and quantitative loci trait analysis to investigate the genetic control of proliferation impairments in NOD thymocytes. RESULTS: Immature thymocytes of female NOD mice proliferate with a relatively low rate compared to non-autoimmune C57Bl/6 mice. This aberrant proliferation was most pronounced in CD4-/lo CD8+ cells differentiating from the CD4-CD8- to the CD4+CD8+ stage. A genetic mapping study using an F2 intercross between the NOD and the C57BL/6 strains showed that a major locus controlling this trait is linked to the insulin-dependent diabetes susceptibility locus Idd6. CONCLUSION/INTERPRETATION: Our results suggest that impairment of proliferation of immature thymocytes is one possible mechanism through which the Idd6 locus contributes to the pathogenesis of diabetes.

CTLA-4-/- mice display T cell-apoptosis resistance resembling that ascribed to autoimmune-prone non-obese diabetic (NOD) mice.

The genes conferring susceptibility to autoimmune (insulin-dependent) diabetes mellitus (IDDM) are, in most cases, not defined. Among the loci so far identified as associated with murine IDDM (Idd1-19), only the nature of Idd1 has been assessed. Here we show that thymocytes and peripheral lymphocytes of the non-obese diabetic (NOD) mouse are relatively resistant to apoptosis induced by gamma-irradiation. By linkage analysis of F2 progeny mice, we map this trait to a locus on chromosome 1 containing the Idd5 diabetes susceptibility region. By the use of congenic mice, we confirm the linkage data and map this locus to a 6 cM region on proximal chromosome 1. Ctla4, being localized in this chromosomal region and mediating crucial functions in T cell biology, is a logical candidate gene in the Idd5 susceptibility region. In line with this, we demonstrate that T cells from Ctla4(-/-)deficient mice show a similar resistance to gamma-irradiation-induced apoptosis as observed in the NOD mice. This reinforces the notion that CTLA-4 contributes to the pathogenesis of autoimmune diabetes.

Diabetes induction in C57BL/6 mice reconstituted with lymphocytes of nonobese diabetic <--> C57BL/6 mouse embryo aggregation chimeras.

To determine whether the genetic background of the insulin-producing beta cells of the pancreas contributes to autoimmune diabetes susceptibility, we have used a model of the disease based on transferring spleen cells from nonobese diabetic (NOD) <--> C57BL/6 (B6) embryo aggregation (EA) chimeras into B6 and NOD irradiated mice. Insulitis and diabetes could be induced into both B6 and NOD hosts, albeit with low incidence. Cyclophosphamide (CY) treatment, known to accelerate diabetes in prediabetic NOD mice, was found to increase diabetes incidence up to 50-60% in both B6 and NOD mice reconstituted with chimeric splenocytes, while diabetes did not occur in CY-treated B6 mice reconstituted with B6 splenocytes. We conclude that the genetic make-up of the target organ does not affect the final stage of the pathogenesis of insulin-dependent diabetes mellitus.

Apoptosis resistance of nonobese diabetic peripheral lymphocytes linked to the Idd5 diabetes susceptibility region.

Defects in lymphocyte apoptosis may lead to autoimmune disorders and contribute to the pathogenesis of type 1 diabetes. Lymphocytes of nonobese diabetic (NOD) mice, an animal model of autoimmune diabetes, have been found resistant to various apoptosis signals, including the alkylating drug cyclophosphamide. Using an F2 intercross between the apoptosis-resistant NOD mouse and the apoptosis-susceptible C57BL/6 mouse, we define a major locus controlling the apoptosis-resistance phenotype and demonstrate its linkage (logarithm of odds score = 3.9) to a group of medial markers on chromosome 1. The newly defined gene cannot be dissociated from Ctla4 and Cd28 and in fact marks a 20-centimorgan region encompassing Idd5, a previously postulated diabetes susceptibility locus. Interestingly, we find that the CTLA-4 (cytotoxic T lymphocyte-associated antigen 4) and the CD28 costimulatory molecules are defectively expressed in NOD mice, suggesting that one or both of these molecules may be involved in the control of apoptosis resistance and, in turn, in diabetes susceptibility.

Establishment and characterization of RAG-2 deficient non-obese diabetic mice.

The authors have established a new immunodeficient mouse strain on the genetic background of the diabetes prone non-obese diabetic (NOD) mouse. A deletion mutant of the RAG-2 gene was back crossed 10 generations onto the NOD/Bom strain background. The homozygous NODrag-2-/- mice lack functionally mature B and T lymphocytes and do not develop insulitis or diabetes throughout life. In contrast, heterozygous NODrag-2+/- develop both insulitis and diabetes with an incidence similar to the wild type NOD mice. In transfer experiments, spleen cells from diabetic NOD donors were found to transfer disease to NODrag-2-/- recipients similar to what has been previously observed in transfer to irradiated NOD recipients or to immunodeficient NOD-scid/scid mice. While resembling the recently established NOD-scid/scid mice in many respects, the NODrag-2-/- mice represents an advantageous model for reconstitution of the pathogenesis of murine IDDM as it does not produce any endogenous, mature T or B lymphocytes.

Programmed cell death in the pathogenesis of murine IDDM: resistance to apoptosis induced in lymphocytes by cyclophosphamide.

The non-obese diabetic (NOD) mouse displays several immune related defects, each of which could potentially contribute to the immunopathogenesis of diabetes that spontaneously develops in these mice. The reported resistance of NOD-lymphocytes to several apoptosis-inducing signals constitutes one such factor. Apoptosis plays a key role in the homeostasis of the immune system, as a means of selecting lymphocyte repertoires both in primary lymphoid organs and in the periphery; distortions in the apoptotic machinery may therefore be hypothesized to be implicated in the pathogenesis of autoimmune disorders. We now report that cyclophosphamide constitutes an apoptosis signal to peripheral lymphocytes and we provide evidence that NOD B cells as well as both CD4 and CD8 T cells display resistance to cyclophosphamide-induced apoptosis. These observations support the notion that apoptosis resistance in NOD mice exists at various levels, and suggest that the CY-sensitive lymphoid population, believed to play an important role in inhibiting the disease in diabetes resistant NOD mice (particularly males), may be controlled by mechanisms that are mediated by apoptosis.