Recombination activating gene-2 (RAG-2) plays a crucial role in the development of lymphocytes by mediating recombination of T cell receptors and immunoglobulins, and loss of RAG-2 causes severe combined immunodeficiency (SCID) in humans. RAG-2 knockout mice created using homologous recombination in ES cells have served as a valuable immunodeficient platform, but concerns have persisted on the specificity of RAG-2-related phenotypes in these animals due to the limitations associated with the genome engineering method used. To precisely investigate the function of RAG-2, we recently established a new RAG-2 knockout FVB mouse line (RAG-2(−/−)) manifesting lymphopenia by employing a CRISPR/Cas9 system at Center for Mouse Models of Human Disease. In this study, we further characterized their phenotypes focusing on histopathological analysis of lymphoid organs. RAG-2(−/−) mice showed no abnormality in development compared to their WT littermates for 26 weeks. At necropsy, gross examination revealed significantly smaller spleens and thymuses in RAG-2(−/−) mice, while histopathological investigation revealed hypoplastic white pulps with intact red pulps in the spleen, severe atrophy of the thymic cortex and disappearance of follicles in lymph nodes. However, no perceivable change was observed in the bone marrow. Moreover, our analyses showed a specific reduction of lymphocytes with a complete loss of mature T cells and B cells in the lymphoid organs, while natural killer cells and splenic megakaryocytes were increased in RAG-2(−/−) mice. These findings indicate that our RAG-2(−/−) mice show systemic lymphopenia with the relevant histopathological changes in the lymphoid organs, suggesting them as an improved Rag-2-related immunodeficient model.
Animals ; Atrophy ; B-Lymphocytes ; Bone Marrow ; Genome ; Homologous Recombination ; Humans ; Immunoglobulins ; Killer Cells, Natural ; Lymph Nodes ; Lymphocytes ; Lymphopenia* ; Megakaryocytes ; Methods ; Mice* ; Mice, Knockout ; Negotiating ; Phenotype ; Receptors, Antigen, T-Cell ; Recombination, Genetic ; Sensitivity and Specificity ; Severe Combined Immunodeficiency ; Spleen ; T-Lymphocytes ; Thymus Gland

CD47 (integrin-associated protein), a multi-spanning transmembrane protein expressed in all cells including red blood cells (RBCs) and leukocytes, interacts with signal regulatory protein α (SIRPα) on macrophages and thereby inhibits phagocytosis of RBCs. Recently, we generated a novel C57BL/6J CD47 knockout (CD47(−/−) hereafter) mouse line by employing a CRISPR/Cas9 system at Center for Mouse Models of Human Disease, and here report their hematological phenotypes. On monitoring their birth and development, CD47(−/−) mice were born viable with a natural male-to-female sex ratio and normally developed from birth through puberty to adulthood without noticeable changes in growth, food/water intake compared to their age and sex-matched wild-type littermates up to 26 weeks. Hematological analysis revealed a mild but significant reduction of RBC counts and hemoglobin in 16 week-old male CD47(−/−) mice which were aggravated at the age of 26 weeks with increased reticulocyte counts and mean corpuscular volume (MCV), suggesting hemolytic anemia. Interestingly, anemia in female CD47(−/−) mice became evident at 26 weeks, but splenomegaly was identified in both genders of CD47(−/−) mice from the age of 16 weeks, consistent with development of hemolytic anemia. Additionally, helper and cytotoxic T cell populations were considerably reduced in the spleen, but not in thymus, of CD47(−/−) mice, suggesting a crucial role of CD47 in proliferation of T cells. Collectively, these findings indicate that our CD47(−/−) mice have progressive hemolytic anemia and splenic depletion of mature T cell populations and therefore may be useful as an in vivo model to study the function of CD47.
Adolescent ; Anemia ; Anemia, Hemolytic* ; Animals ; Erythrocyte Indices ; Erythrocytes ; Female ; Humans ; Leukocytes ; Macrophages ; Male ; Mice* ; Parturition ; Phagocytosis ; Phenotype ; Puberty ; Reticulocyte Count ; Sex Ratio ; Spleen ; Splenomegaly* ; T-Lymphocytes ; Thymus Gland