ABSTRACT
Most humans with autoimmune lymphoproliferative syndrome (ALPS) carry heterozygous dominant mutations in one allele of the gene encoding Fas/APO-1/CD95. ALPS patients, like Fas-deficient MRL lpr/lpr mice, have lymphoproliferation, autoimmunity, increased CD4(-)/CD8(-) T lymphocytes, and apoptosis defects. Consistent with the phenotypic variability of lpr/lpr mice of different background strains, human genetic studies indicate that a Fas mutation is insufficient to induce ALPS in all mutation carriers. To investigate the dominant function of human Fas mutations and the additional genetic factor(s) involved in the development of ALPS, we generated transgenic mice expressing, in addition to endogenous Fas, mouse Fas molecules bearing mutations in the intracellular death domain corresponding to mutations identified in ALPS patients. Transgenic mice developed mild features of ALPS, including hepatosplenomegaly, elevated proportions of lymphocytes in spleen and lymph nodes, apoptotic defects, and hepatic lymphocytic infiltrates. Therefore defective murine Fas proteins act in a dominant manner to impair apoptosis of activated lymphocytes and disrupt lymphocyte homeostasis. The influence of genetic background on phenotype was studied by comparing transgenic mice on FVB/N and (FVB/N x MRL) backgrounds with syngenetic control mice and with MRL and MRL lpr/lpr mice. While expression of transgenic mutant Fas contributed mainly to hepatosplenomegaly and accumulation of lymphocytes, MRL background genes played a major role in the production of autoantibodies and elevated serum immunoglobulin levels. Moreover, compared to FVB/N (+/+) mice, a substantial Fas-specific apoptotic defect was found in MRL (+/+) mice, suggesting a mechanism for the known tendency of this strain to develop autoimmunity.
Subject(s)
Lymphoproliferative Disorders/immunology , Membrane Glycoproteins/genetics , Animals , Antibodies, Antinuclear/analysis , Antigens, Surface/analysis , Apoptosis/immunology , Autoimmune Diseases/genetics , Fas Ligand Protein , Genes, Dominant , Humans , Liver/chemistry , Liver/pathology , Liver Diseases/genetics , Lymph Nodes/chemistry , Lymph Nodes/pathology , Lymphatic Diseases/genetics , Lymphoproliferative Disorders/genetics , Mice , Mice, Inbred MRL lpr , Mice, Transgenic , Mutation , Phenotype , Spleen/chemistry , Spleen/pathology , Splenomegaly/genetics , T-Lymphocytes/cytologyABSTRACT
The hemoglobin-deficit mouse mutant (hbd) is characterized by a severe microcytic anemia that is inherited in an autosomal-recessive manner. Previous results from our laboratory indicated that normal mice develop anemia if they are transplanted with bone marrow from mutant animals. Furthermore, we demonstrated a delay in erythroid reconstitution from hbd marrow compared to normal marrow. Although these experiments show a defect that is intrinsic to hbd marrow, it is unclear if the hbd phenotype is solely the result of a bone marrow-derived defect. To exclude an environmental influence on hbd anemia, we attempted to cure the defect by transplanting normal marrow into the hbd mouse. We observed that the transplanted animals converted to a normal phenotype. These results indicated that the defect is bone marrow derived. In contrast to the microcytosis mutant whose defective gene is ubiquitously expressed, our data suggest that the defective gene product is specific to hematopoietic cells.
Subject(s)
Hemoglobins/deficiency , Anemia/blood , Anemia/therapy , Animals , Blood Cell Count , Bone Marrow Transplantation , Cell Lineage/genetics , Erythrocyte Indices , Erythrocytes/physiology , Female , Glucose-6-Phosphate Isomerase/genetics , Male , Mice , Mice, Inbred C57BL , Mice, Mutant Strains , Time FactorsSubject(s)
Chromosome Mapping , Hemoglobins/deficiency , Hemoglobins/genetics , Animals , Crosses, Genetic , Female , Ferritins/genetics , Genetic Linkage , Genetic Markers , Heterozygote , Homozygote , Male , Mice , Mice, Inbred C57BL , MuridaeABSTRACT
The mouse mutant hemoglobin deficit (gene symbol hbd) is characterized by a severe microcytic anemia that is inherited in an autosomal-recessive manner. To assess the mutation's effect on hematopoiesis, unfractionated bone marrow (BM) from either a mutant C57BL6/J-hbd/hbd, Gpi1b/Gpi1b (phenotype symbol HBD), or normal C57BL6/J-+hbd/+hbd, Gpi1b/Gpi1b mouse was injected intravenously into irradiated congenic C57BL6/J-+hbd/+hbd, Gpi1a/Gpi1a, lgh(a)/lgh(a), Thy1a/Thy1a mice. The congenic recipients of mutant or normal marrow obtained complete red blood cell (RBC) and leukocyte reconstitution, with the exception of one recipient of HBD marrow. After 24 weeks posttransplantation, the normal recipients of HBD marrow obtained a microcytic anemia similar to the donor. These results suggest that the HBD phenotype is caused by a BM defect. We observed that the erythroid lineage derived from donor HBD marrow repopulated more slowly than the normal marrow at 4 weeks post-transplantation. To determine if this difference was a result of an erythropoietic defect, competitive repopulation was performed using either mutant or normal marrow competed against normal congenic marrow. For the erythroid lineage, no significant contribution from HBD marrow was observed. To assess if the RBC block was based on a deficiency of myeloid progenitors, both in vitro and in vivo assays were performed: absolute numbers of bone progenitors were increased, suggesting that the defect results in a late block to erythroid differentiation.
