RESUMO
CD4(+) T-helper type 2 (T(H)2) cells, characterized by their expression of interleukin (IL)-4, IL-5, IL-9 and IL-13, are required for immunity to helminth parasites and promote the pathological inflammation associated with asthma and allergic diseases. Polymorphisms in the gene encoding the cytokine thymic stromal lymphopoietin (TSLP) are associated with the development of multiple allergic disorders in humans, indicating that TSLP is a critical regulator of T(H)2 cytokine-associated inflammatory diseases. In support of genetic analyses, exaggerated TSLP production is associated with asthma, atopic dermatitis and food allergies in patients, and studies in murine systems demonstrated that TSLP promotes T(H)2 cytokine-mediated immunity and inflammation. However, the mechanisms through which TSLP induces T(H)2 cytokine responses remain poorly defined. Here we demonstrate that TSLP promotes systemic basophilia, that disruption of TSLP-TSLPR interactions results in defective basophil responses, and that TSLPR-sufficient basophils can restore T(H)2-cell-dependent immunity in vivo. TSLP acted directly on bone-marrow-resident progenitors to promote basophil responses selectively. Critically, TSLP could elicit basophil responses in both IL-3-IL-3R-sufficient and -deficient environments, and genome-wide transcriptional profiling and functional analyses identified heterogeneity between TSLP-elicited versus IL-3-elicited basophils. Furthermore, activated human basophils expressed TSLPR, and basophils isolated from eosinophilic oesophagitis patients were distinct from classical basophils. Collectively, these studies identify previously unrecognized heterogeneity within the basophil cell lineage and indicate that expression of TSLP may influence susceptibility to multiple allergic diseases by regulating basophil haematopoiesis and eliciting a population of functionally distinct basophils that promote T(H)2 cytokine-mediated inflammation.
Assuntos
Basófilos/citologia , Citocinas/metabolismo , Hematopoese , Hipersensibilidade Imediata/imunologia , Inflamação/imunologia , Inflamação/metabolismo , Interleucina-3 , Animais , Asma/imunologia , Basófilos/metabolismo , Citocinas/genética , Citocinas/imunologia , Dermatite Atópica/imunologia , Hipersensibilidade Alimentar/imunologia , Humanos , Interleucina-3/metabolismo , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos C57BL , Fenótipo , Receptores de Citocinas/metabolismo , Receptores de Interleucina-3/deficiência , Receptores de Interleucina-3/genética , Receptores de Interleucina-3/metabolismo , Células Th2/imunologia , Linfopoietina do Estroma do TimoRESUMO
Basophils are recognized as immune modulators through their ability to produce IL-4, a key cytokine required for Th2 immunity. It has also recently been reported that basophils are transiently recruited into the draining lymph node (LN) after allergen immunization and that the recruited basophils promote the differentiation of naive CD4 T cells into Th2 effector cells. Using IL-3(-/-) and IL-3Rbeta(-/-) mice, we report in this study that the IL-3/IL-3R system is absolutely required to recruit circulating basophils into the draining LN following helminth infection. Unexpectedly, the absence of IL-3 or of basophil LN recruitment played little role in helminth-induced Th2 immune responses. Moreover, basophil depletion in infected mice did not diminish the development of IL-4-producing CD4 T cells. Our results reveal a previously unknown role of IL-3 in recruiting basophils to the LN and demonstrate that basophils are not necessarily associated with the development of Th2 immunity during parasite infection.
Assuntos
Basófilos/imunologia , Basófilos/patologia , Movimento Celular/imunologia , Interleucina-3/fisiologia , Linfonodos/imunologia , Linfonodos/patologia , Infecções por Strongylida/imunologia , Células Th2/imunologia , Animais , Basófilos/parasitologia , Movimento Celular/genética , Técnicas de Introdução de Genes , Interleucina-3/deficiência , Interleucina-3/genética , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Knockout , Nippostrongylus/imunologia , Receptores de Interleucina-3/deficiência , Receptores de Interleucina-3/genética , Receptores de Interleucina-3/fisiologia , Infecções por Strongylida/parasitologia , Infecções por Strongylida/patologia , Células Th2/parasitologiaRESUMO
Deficiency of the granulocyte-macrophage colony-stimulating factor (GM-CSF)/interleukin-3 (IL-3)/IL-5 receptors common beta chain (betac) is a cause of fatal respiratory failure. betac deficiency manifests as pulmonary alveolar proteinosis (PAP). PAP has heterogenous etiologies that may be genetic or aquired. Some cases of PAP have been reported to be associated with hematologic malignancies such as acute myeloid leukemia (AML). In mice, the PAP phenotype was generated by targeted deletion of the gene for betac and can be treated by transplantation of wild-type bone marrow into betac -/- mice. Thus, our findings in betac -/- mice provide evidence for a causal relationship between the lung disease and the hematopoietic system. We describe here expression defects of betac or betac plus GM-CSF receptor alpha chain (GM-CSFR alpha) in 3 pediatric patients with AML and PAP symptoms. All of the patients' leukemic cells failed to express normal levels of betac. The leukemic cells of patients no. 2 and 3 additionally lacked the expression of GM-CSFR alpha, as shown by flow cytometry. Strikingly reduced or absent function of betac was demonstrated in clonogenic progenitor assays with absent colony-forming unit (CFU) growth after GM-CSF or IL-3 stimulation. The response to growth factors acting via a growth factor receptor distinct from the GM-CSF/IL-3/IL-5 system (recombinant human granulocyte colony-stimulating factor [rhG-CSF]) was normal. After antileukemic treatment, the pulmonary symptoms resolved and betac or betac plus GM-CSFR alpha expression was normal. Our findings provide evidence that a defect in the expression of betac or betac plus GM-CSFR alpha on AML blasts can be associated with respiratory failure in patients with AML.
Assuntos
Regulação Leucêmica da Expressão Gênica , Leucemia Mieloide/complicações , Proteinose Alveolar Pulmonar/etiologia , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/deficiência , Receptores de Interleucina-3/deficiência , Receptores de Interleucina/deficiência , Insuficiência Respiratória/etiologia , Doença Aguda , Adulto , Animais , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Transplante de Medula Óssea , Líquido da Lavagem Broncoalveolar/química , Líquido da Lavagem Broncoalveolar/citologia , Linhagem da Célula , Criança , Evolução Fatal , Feminino , Humanos , Lactente , Leucemia Monocítica Aguda/complicações , Leucemia Monocítica Aguda/genética , Leucemia Monocítica Aguda/terapia , Leucemia Mieloide/tratamento farmacológico , Leucemia Mieloide/genética , Leucemia Mielomonocítica Aguda/complicações , Leucemia Mielomonocítica Aguda/tratamento farmacológico , Leucemia Mielomonocítica Aguda/genética , Macrófagos Alveolares/patologia , Masculino , Camundongos , Camundongos Knockout , Proteinose Alveolar Pulmonar/diagnóstico , Proteinose Alveolar Pulmonar/genética , Surfactantes Pulmonares/análise , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/biossíntese , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/química , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/genética , Receptores de Interleucina/biossíntese , Receptores de Interleucina/química , Receptores de Interleucina/genética , Receptores de Interleucina-3/biossíntese , Receptores de Interleucina-3/química , Receptores de Interleucina-3/genética , Receptores de Interleucina-5RESUMO
The receptors for interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-5 share a common signaling subunit betac. However, in the mouse, there is an additional IL-3 signaling protein, betaIL-3, which is specific for IL-3. We have previously reported that IL-3 abrogates the lymphoid potentials of murine lymphohematopoietic progenitors and the reconstituting ability of hematopoietic stem cells. We used bone marrow cells from betac- and betaIL-3-knock-out mice to examine the relative contributions of the receptor proteins to the negative regulation by IL-3. First, we tested the effects of IL-3 on lymphohematopoietic progenitors by using lineage-negative (Lin-) marrow cells of 5-fluorouracil (5-FU)-treated mice in the two-step methylcellulose culture we reported previously. Addition of IL-3 to the combination of steel factor (SF, c-kit ligand) and IL-11 abrogated the B-lymphoid potential of the marrow cells of both types of knock-out mice as well as wild-type mice. Next, we investigated the effects of IL-3 on in vitro expansion of the hematopoietic stem cells. We cultured Lin-Sca-1-positive, c-kit-positive marrow cells from 5-FU-treated mice in suspension in the presence of SF and IL-11 with or without IL-3 for 7 days and tested the reconstituting ability of the cultured cells by transplanting the cells into lethally irradiated Ly-5 congenic mice together with "compromised" marrow cells. Presence of IL-3 in culture abrogated the reconstituting ability of the cells from both types of knock-out mice and the wild-type mice. In contrast, addition of GM-CSF to the suspension culture abrogated neither B-cell potential nor reconstituting abilities of the cultured cells of wild-type mice. These observations may have implications in the choice of cytokines for use in in vitro expansion of human hematopoietic stem cells and progenitors.
Assuntos
Linfócitos B/citologia , Fator Estimulador de Colônias de Granulócitos e Macrófagos/farmacologia , Inibidores do Crescimento/farmacologia , Células-Tronco Hematopoéticas/efeitos dos fármacos , Interleucina-3/farmacologia , Receptores de Interleucina-3/fisiologia , Transdução de Sinais/fisiologia , Animais , Células Cultivadas , Feminino , Sobrevivência de Enxerto/efeitos dos fármacos , Transplante de Células-Tronco Hematopoéticas , Células-Tronco Hematopoéticas/citologia , Humanos , Interleucina-11/farmacologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Conformação Proteica , Quimera por Radiação , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/química , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/fisiologia , Receptores de Interleucina/química , Receptores de Interleucina-3/química , Receptores de Interleucina-3/deficiência , Receptores de Interleucina-3/efeitos dos fármacos , Receptores de Interleucina-3/genética , Receptores de Interleucina-5 , Proteínas Recombinantes/farmacologia , Transdução de Sinais/efeitos dos fármacos , Fator de Células-Tronco/farmacologia , Especificidade por SubstratoRESUMO
Thrombopoietin is a lineage-dominant cytokine involved primarily in the control of platelet production. The physiological importance of thrombopoietin (TPO) in the regulation of megakaryocyte and platelet production was demonstrated by the production of mice deficient in TPO or its receptor, c-Mpl. Even though these mice are profoundly thrombocytopenic they maintain a basal level of approximately 10% of the normal count of fully functional platelets. These platelets prevent any abnormal bleeding episodes and highlight the potential importance of other factors in the control of platelet production. Among the factors with in vitro megakaryocytopoietic activity, the most potent is undoubtedly interleukin 3 (IL-3). To analyze the contribution of IL-3 to platelet formation in the absence of TPO, we have generated mice deficient in both c-Mpl and IL-3Ralpha by taking advantage of a natural mutation present in this gene in the A/J mouse. Surprisingly, these double knockout mice did not show any further reduction in their platelet or megakaryocyte counts when compared with c-Mpl-deficient mice. Similarly, progenitors from other lineages that are also reduced in c-Mpl-deficient mice are not further affected by the absence of a functional IL-3Ralpha gene. These results demonstrate that IL-3 alone is not responsible for the production of a basal level of normal platelets in the absence of thrombopoietin signaling.
Assuntos
Plaquetas/efeitos dos fármacos , Interleucina-3/farmacologia , Proteínas de Neoplasias , Proteínas Proto-Oncogênicas/deficiência , Receptores de Citocinas , Receptores de Interleucina-3/deficiência , Trombopoetina/deficiência , Animais , Contagem de Células Sanguíneas , Plaquetas/citologia , Plaquetas/metabolismo , Exame de Medula Óssea , Células Cultivadas , Interleucina-3/metabolismo , Camundongos , Camundongos Knockout , Proteínas Proto-Oncogênicas/genética , Receptores de Interleucina-3/genética , Receptores de Trombopoetina , Células-Tronco/citologia , Trombopoetina/genéticaRESUMO
Pulmonary alveolar proteinosis (PAP) is a heterogeneous disorder of genetic or acquired etiologies. In some cases congenital PAP is associated with hereditary surfactant protein (SP)-B deficiency. To date, the molecular defect in the majority of patients with PAP has not been identified. In mice, PAP has been generated by targeted deletion of the genes for either the GM-CSF/IL-3/IL-5 receptor common beta chain (beta c) or GM-CSF. Here, we describe an expression defect of beta c in three of seven pediatric patients with PAP and in one patient with severe lung disease suspected to be PAP. The patients failed to express normal levels of beta c as shown by flow cytometry. Strikingly reduced or absent function of beta c was demonstrated by ligand binding studies and progenitor clonogenic assays. Analysis of beta c DNA revealed a point mutation from proline to threonine at codon 602 in one patient. Our findings provide evidence that a defect in the expression of a hematopoietic cytokine receptor is associated with human PAP.
Assuntos
Proteinose Alveolar Pulmonar/metabolismo , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/deficiência , Receptores de Interleucina-3/deficiência , Receptores de Interleucina/deficiência , Adulto , Substituição de Aminoácidos , Pré-Escolar , Fator Estimulador de Colônias de Granulócitos e Macrófagos/metabolismo , Hematopoese , Humanos , Lactente , Cinética , Mutação Puntual , Proteolipídeos/metabolismo , Surfactantes Pulmonares/metabolismo , Receptores de Interleucina-5Assuntos
Camundongos Knockout , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/deficiência , Receptores de Interleucina-3/deficiência , Receptores de Interleucina/deficiência , Animais , Transplante de Medula Óssea , Doenças Hematológicas/etiologia , Humanos , Camundongos , Proteinose Alveolar Pulmonar/etiologia , Receptores de Interleucina-5RESUMO
Mice deficient for the IL-3/GM-CSF/IL-5 beta c receptor (beta cR KO) develop lung disease similar to that seen in human pulmonary alveolar proteinosis (PAP) which includes lymphocytic infiltration around airways and vessels and the progressive accumulation of surfactant and macrophages within the alveolar space. We investigated bone marrow transplantation (BMT) as a curative treatment of PAP in beta cR KO mice by semiquantitative histologic analysis and evaluation of pulmonary function. BMT from wild-type (WT) donors into lethally irradiated beta cR KO recipients (WT --> KO) led to the complete resolution of alveolar protein accumulation and to normalization of BAL fluid cellularity and macrophage morphology. However, detailed microscopic analysis of lung tissue revealed the persistence of significant cellular infiltrates in WT --> KO recipients which were equivalent to those seen in KO --> KO animals. Evaluation of pulmonary function demonstrated that only dynamic compliance (Cdyn) and not airway conductance (G[L]) was significantly improved in the WT --> KO group compared to KO --> KO animals and that both of these measurements remained significantly abnormal when compared to WT --> WT controls. We conclude, that although BMT for PAP reverses alveolar macrophage and protein accumulation, it does not decrease the interstitial inflammatory component of this disease. The importance of this residual pathology is demonstrated by the incomplete correction of alveolar function (Cdyn) and lack of improvement in increased airway resistance (G[L]). These findings may have important implications with regard to the extent that BMT can be considered a potential curative procedure for this clinical disorder.
Assuntos
Transplante de Medula Óssea , Pulmão/patologia , Proteinose Alveolar Pulmonar/patologia , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/deficiência , Receptores de Interleucina-3/deficiência , Receptores de Interleucina/deficiência , Animais , Líquido da Lavagem Broncoalveolar/citologia , Modelos Animais de Doenças , Humanos , Complacência Pulmonar , Camundongos , Camundongos Knockout , Proteinose Alveolar Pulmonar/terapia , Receptores de Interleucina-5RESUMO
Interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-5 are major hematopoietic cytokines produced by activated T cells and exhibit similar biologic activities by signaling through a common receptor subunit (beta c). Mice lacking beta c show a pulmonary alveolar proteinosis-like disease and reduced numbers of peripheral eosinophils, which are explained by the lack of GM-CSF and IL-5 function, respectively. However, beta c-deficient hematopoietic cells do respond to IL-3 normally, probably through an additional beta subunit of the IL-3 receptor (beta IL3) that is present in the mouse. Thus, almost normal hematopoiesis in beta c-deficient mice may be caused by functional redundancy between IL-3 and GM-CSF. To clarify the role of the entire IL-3/GM-CSF/IL-5 system in hematopoiesis in vivo, we crossed the beta c mutant mice with mice deficient for IL-3 ligand to generate mice lacking the entire IL-3/GM-CSF/IL-5 functions. The double-mutant mice were apparently normal and fertile. The severity of the lung pathology in the beta c/IL-3 double-mutant mice showed normal hemodynamic parameters except for reduced numbers of eosinophils and the lack of eosinophilic response to parasites, which were also found in beta c mutant mice. The immune response of the beta c/IL-3 double-mutant mice to Listeria mono-cytogenes was normal, as was hematopoietic recovery after administration of the cytotoxic drug, 5-fluorouracil. Although it has been believed that IL-3/GM-CSF/IL-5 produced by activated T cells play a major role in expansion of hematopoietic cells in emergency, our results indicate that the entire function of IL-3/GM-CSF/IL-5 is dispensable for hematopoiesis in emergency as well as in the steady state. Thus, there must be an alternative mechanism to produce blood cells in both situations.
Assuntos
Fator Estimulador de Colônias de Granulócitos e Macrófagos/fisiologia , Hematopoese , Interleucina-3/fisiologia , Interleucina-5/fisiologia , Pneumopatias/genética , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/deficiência , Receptores de Interleucina-3/deficiência , Receptores de Interleucina/deficiência , Animais , Medula Óssea/efeitos dos fármacos , Medula Óssea/patologia , Cruzamentos Genéticos , Eosinófilos/patologia , Fluoruracila/toxicidade , Imunocompetência , Leucopenia/genética , Leucopenia/patologia , Listeriose/imunologia , Pneumopatias/patologia , Macrófagos Alveolares/patologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Nippostrongylus , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/química , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/genética , Receptores de Interleucina/química , Receptores de Interleucina/genética , Receptores de Interleucina-3/química , Receptores de Interleucina-3/genética , Receptores de Interleucina-5 , Infecções por Strongylida/imunologiaRESUMO
Hematopoietic progenitor cells of the A/J strain of mice show a pronounced defect in the ability to form colonies or proliferate in response to interleukin-3 (IL-3). Comparison of immunoblots of A/J mast cells and of mast cells from the C57BL/6 strain that respond normally to IL-3 showed that, in both strains, a 125-kD band of the expected size was recognized by an antibody against the beta chain of the IL-3 receptor, the AIC2A molecule. However, in the C57BL/6 cells, there was an additional 110-kD species not seen in cells of the A/J strain. Analyses using bone marrow-derived mast cells from a panel of A/J x C57BL/6 and A/J x C57BL/6 recombinant inbred (RI) mice showed that the hypo-responsiveness to IL-3 is governed by a single gene. However, the absence of this 110-kD species in the A/J strain did not co-map with IL-3 hypo-responsiveness but did indeed map to the AIC2A genetic locus. These data show that this trait in the A/J strain was due to a polymorphism of the AIC2A gene unrelated to IL-3 hypo-responsiveness. Typing of the RI strains for the markers D14Mit98, D14Mitl4, and D14Mit133 mapped the locus determining hypo-responsiveness to IL-3 to the subtelomeric region of chromosome 14, the region that also bears the gene encoding the alpha chain of the IL-3 receptor (lL-3Ralpha). Immunofluorescence analyses indicated that IL-3Ralpha protein was undetectable on fresh bone marrow cells from A/J mice, although clearly detectable on cells from the responder C57BL/6 strain. However, IL-3Ralpha was readily detectable at normal levels on A/J mast cells generated by culture of A/J bone marrow cells in a combination of IL-3 and steel factor. Moreover, IL-3Ralpha on these A/J mast cells appears to be functional in that IL-3 stimulation of these cells results in tyrosine phosphorylation events characteristic of IL-3 signaling, including tyrosine phosphorylation of the beta chain of the IL-3 receptor, Jak-2 kinase, and SHPTP2. Collectively, these data indicate that the hypo-responsiveness of A/J mice to IL-3 is due to a defect in the gene encoding IL-3Ralpha and that, although this defect gives rise to reduced expression of alpha chain on primary bone marrow cells, this defect is not absolute and that, under certain circumstances, A/J cells can express functional receptors.
Assuntos
Hematopoese/efeitos dos fármacos , Interleucina-3/farmacologia , Camundongos Endogâmicos A/genética , Receptores de Interleucina-3/deficiência , Animais , Sequência de Bases , Células Cultivadas , Mapeamento Cromossômico , Expressão Gênica , Células-Tronco Hematopoéticas/efeitos dos fármacos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos DBA , Dados de Sequência Molecular , Polimorfismo Genético , Receptores de Interleucina-3/química , Receptores de Interleucina-3/efeitos dos fármacos , Receptores de Interleucina-3/genética , Proteínas Recombinantes/farmacologia , Transdução de Sinais/efeitos dos fármacos , Especificidade da Espécie , Fator de Células-Tronco/farmacologiaRESUMO
Gene targeting was used to create mice with a null mutation of the gene encoding the common beta subunit (beta C) of the granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 3 (IL-3; multi-CSF), and interleukin 5 (IL-5) receptor complexes (beta C-/- mice). High-affinity binding of GM-CSF was abolished in beta C-/- bone marrow cells, while cells from heterozygous animals (beta C+/- mice) showed an intermediate number of high-affinity receptors. Binding of IL-3 was unaffected, confirming that the IL-3-specific beta chain remained intact. Eosinophil numbers in peripheral blood and bone marrow of beta C-/- animals were reduced, while other hematological parameters were normal. In clonal cultures of beta C-/- bone marrow cells, even high concentrations of GM-CSF and IL-5 failed to stimulate colony formation, but the cells exhibited normal quantitative responsiveness to stimulation by IL-3 and other growth factors. beta C-/- mice exhibited normal development and survived to young adult life, although they developed pulmonary peribronchovascular lymphoid infiltrates and areas resembling alveolar proteinosis. There was no detectable difference in the systemic clearance and distribution of GM-CSF between beta C-/- and wild-type littermates. The data establish that beta C is normally limiting for high-affinity binding of GM-CSF and demonstrate that systemic clearance of GM-CSF is not mediated via such high-affinity receptor complexes.
Assuntos
Medula Óssea/patologia , Pulmão/patologia , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/deficiência , Receptores de Interleucina/deficiência , Animais , Células da Medula Óssea , Divisão Celular , Fator Estimulador de Colônias de Granulócitos e Macrófagos/farmacocinética , Hematopoese/fisiologia , Células-Tronco Hematopoéticas/citologia , Interleucina-3/metabolismo , Camundongos , Camundongos Mutantes , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/genética , Receptores de Interleucina/genética , Receptores de Interleucina-3/deficiência , Receptores de Interleucina-3/genética , Receptores de Interleucina-5RESUMO
Interleukin-3 (IL-3) stimulates colony formation of multiple lineages of hematopoietic cells. Bone marrow cells of A/J mice are nonresponsive to IL-3, and this observation has recently been correlated with aberrant mRNA splicing and impaired expression of the IL-3 receptor alpha subunit (IL-3R alpha), a binding component of the high-affinity receptors. We examined the IL-3R alpha gene in 27 inbred mouse strains and found the identical mutation, a 5-bp deletion at the branch point of intron 7, in 10 of these mouse strains. Bone marrow cells isolated from these 10 mouse strains did not express IL-3R alpha on the cell surface and did not form colonies in response to IL-3. Because the defective IL-3R alpha gene was found in several distantly related mouse strains, it appears to be a recessive allele rather than a sporadic mutation. In contrast, only 1 of 21 wild-derived mouse strains carried the 5-bp deletion in the IL-3R alpha gene. This study suggests that IL-3 function is not required for normal hematopoiesis in mice, but the retention of the IL-3 and IL-3R system may be of some selective advantage in wild populations.