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BACKGROUND Human rhinoviruses (HRVs) are a major trigger of asthma exacerbations,with the bronchial epithelium being the major site of HRV infection and replication. Mast cells (MCs) play a key role in asthma where their numbers are increased in the bronchial epithelium with increasing disease severity. OBJECTIVE In view of the emerging role of MCs in innate immunity and increased localization to the asthmatic bronchial epithelium,we investigated whether HRV infection of MCs generated innate immune responses which were protective against infection. METHODS The LAD2 MC line or primary human cord blood-derived MCs (CBMCs) were infected with HRV or UV-irradiated HRV at increasing multiplicities of infection (MOI) without or with IFN-β or IFN-λ. After 24 h,innate immune responses were assessed by RT-qPCR and IFN protein release by ELISA. Viral replication was determined by RT-qPCR and virion release by TCID50 assay. RESULTS HRV infection of LAD2 MCs induced expression of IFN-β,IFN-λ and IFN-stimulated genes. However,LAD2 MCs were permissive for HRV replication and release of infectious HRV particles. Similar findings were observed with CBMCs. Neutralization of the type I IFN receptor had minimal effects on viral shedding,suggesting that endogenous type I IFN signalling offered limited protection against HRV. However,augmentation of these responses by exogenous IFN-β,but not IFN-λ,protected MCs against HRV infection. CONCLUSION AND CLINICAL RELEVANCE MCs are permissive for the replication and release of HRV,which is prevented by exogenous IFN-β treatment. Taken together,these findings suggest a novel mechanism whereby MCs may contribute to HRV-induced asthma exacerbations. View Publication

Current combination antiretroviral therapies (cART) efficiently suppress HIV-1 reproduction in humans,but the virus persists as integrated proviral reservoirs in small numbers of cells. To generate an antiviral agent capable of eradicating the provirus from infected cells,we employed 145 cycles of substrate-linked directed evolution to evolve a recombinase (Brec1) that site-specifically recognizes a 34-bp sequence present in the long terminal repeats (LTRs) of the majority of the clinically relevant HIV-1 strains and subtypes. Brec1 efficiently,precisely and safely removes the integrated provirus from infected cells and is efficacious on clinical HIV-1 isolates in vitro and in vivo,including in mice humanized with patient-derived cells. Our data suggest that Brec1 has potential for clinical application as a curative HIV-1 therapy. View Publication

Gaucher disease is caused by an inherited deficiency of glucocerebrosidase that manifests with storage of glycolipids in lysosomes,particularly in macrophages. Available cell lines modeling Gaucher disease do not demonstrate lysosomal storage of glycolipids; therefore,we set out to develop two macrophage models of Gaucher disease that exhibit appropriate substrate accumulation. We used these cellular models both to investigate altered macrophage biology in Gaucher disease and to evaluate candidate drugs for its treatment. We generated and characterized monocyte-derived macrophages from 20 patients carrying different Gaucher disease mutations. In addition,we created induced pluripotent stem cell (iPSC)-derived macrophages from five fibroblast lines taken from patients with type 1 or type 2 Gaucher disease. Macrophages derived from patient monocytes or iPSCs showed reduced glucocerebrosidase activity and increased storage of glucocerebroside and glucosylsphingosine in lysosomes. These macrophages showed efficient phagocytosis of bacteria but reduced production of intracellular reactive oxygen species and impaired chemotaxis. The disease phenotype was reversed with a noninhibitory small-molecule chaperone drug that enhanced glucocerebrosidase activity in the macrophages,reduced glycolipid storage,and normalized chemotaxis and production of reactive oxygen species. Macrophages differentiated from patient monocytes or patient-derived iPSCs provide cellular models that can be used to investigate disease pathogenesis and facilitate drug development. View Publication

Transient lymphopenia is a hallmark of measles virus (MV)-induced immunosuppression. To address to what extent replenishment of the peripheral lymphocyte compartment from bone marrow (BM) progenitor/stem cells might be affected,we analyzed the interaction of wild-type MV with hematopoietic stem and progenitor cells (HS/PCs) and stroma cells in vitro. Infection of human CD34(+) HS/PCs or stroma cells with wild-type MV is highly inefficient yet noncytolytic. It occurs independently of CD150 in stroma cells but also in HS/PCs,where infection is established in CD34(+) CD150(-) and CD34(+) CD150(+) (in humans representing HS/PC oligopotent precursors) subsets. Stroma cells and HS/PCs can mutually transmit MV and may thereby create a possible niche for continuous viral exchange in the BM. Infected lymphocytes homing to this compartment may serve as sources for HS/PC or stroma cell infection,as reflected by highly efficient transmission of MV from both populations in cocultures with MV-infected B or T cells. Though MV exposure does not detectably affect the viability,expansion,and colony-forming activity of either CD150(+) or CD150(-) HS/PCs in vitro,it efficiently interferes with short- but not long-term hematopoietic reconstitution in NOD/SCID mice. Altogether,these findings support the hypothesis that MV accession of the BM compartment by infected lymphocytes may contribute to peripheral blood mononuclear cell lymphopenia at the level of BM suppression. View Publication

The lipocalin mouse 24p3 has been implicated in diverse physiological processes,including apoptosis,iron trafficking,development and innate immunity. Studies from our laboratory as well as others demonstrated the proapoptotic activity of 24p3 in a variety of cultured models. However,a general role for the lipocalin 24p3 in the hematopoietic system has not been tested in vivo. To study the role of 24p3,we derived 24p3 null mice and back-crossed them onto C57BL/6 and 129/SVE backgrounds. Homozygous 24p3(-/-) mice developed a progressive accumulation of lymphoid,myeloid,and erythroid cells,which was not due to enhanced hematopoiesis because competitive repopulation and recovery from myelosuppression were the same as for wild type. Instead,apoptotic defects were unique to many mature hematopoietic cell types,including neutrophils,cytokine-dependent mast cells,thymocytes,and erythroid cells. Thymocytes isolated from 24p3 null mice also displayed resistance to apoptosis-induced by dexamethasone. Bim response to various apoptotic stimuli was attenuated in 24p3(-/-) cells,thus explaining their resistance to the ensuing cell death. The results of these studies,in conjunction with those of previous studies,reveal 24p3 as a regulator of the hematopoietic compartment with important roles in normal physiology and disease progression. Interestingly,these functions are limited to relatively mature blood cell compartments. View Publication

Mast cells (MCs) play an important role in the regulation of protective adaptive immune responses against pathogens. However,it is still unclear whether MCs promote such host defense responses via direct effects on T cells or rather by modifying the functions of antigen-presenting cells. To identify the underlying mechanisms of the immunoregulatory capacity of MCs,we investigated the impact of MCs on dendritic cell (DC) maturation and function. We found that murine peritoneal MCs underwent direct crosstalk with immature DCs that induced DC maturation as evidenced by enhanced expression of costimulatory molecules. Furthermore,the MC/DC interaction resulted in the release of the T-cell modulating cytokines IFN-γ,IL-2,IL-6 and TGF-β into coculture supernatants and increased the IL-12p70,IFN-γ,IL-6 and TGF-β secretion of LPS-matured DCs. Such MC-primed" DCs subsequently induced efficient CD4+ T-cell proliferation. Surprisingly� View Publication

CD4(+) T cells play a key role in host defense against Pneumocystis infection. To define the role of naïve CD4(+) T cell production through the thymopoietic response in host defense against Pneumocystis infection,Pneumocystis murina infection in the lung was induced in adult male C57BL/6 mice with and without prior thymectomy. Pneumocystis infection caused a significant increase in the number of CCR9(+) multipotent progenitor (MPP) cells in the bone marrow and peripheral circulation,an increase in populations of earliest thymic progenitors (ETPs) and double negative (DN) thymocytes in the thymus,and recruitment of naïve and total CD4(+) T cells into the alveolar space. The level of murine signal joint T cell receptor excision circles (msjTRECs) in spleen CD4(+) cells was increased at 5 weeks post-Pneumocystis infection. In thymectomized mice,the numbers of naïve,central memory,and total CD4(+) T cells in all tissues examined were markedly reduced following Pneumocystis infection. This deficiency of naïve and central memory CD4(+) T cells was associated with delayed pulmonary clearance of Pneumocystis. Extracts of Pneumocystis resulted in an increase in the number of CCR9(+) MPPs in the cultured bone marrow cells. Stimulation of cultured bone marrow cells with ligands to Toll-like receptor 2 ([TLR-2] zymosan) and TLR-9 (ODN M362) each caused a similar increase in CCR9(+) MPP cells via activation of the Jun N-terminal protein kinase (JNK) pathway. These results demonstrate that enhanced production of naïve CD4(+) T lymphocytes through the thymopoietic response and enhanced delivery of lymphopoietic precursors from the bone marrow play an important role in host defense against Pneumocystis infection. View Publication

Severe congenital neutropenia (SCN) is an inborn disorder of granulopoiesis that in many cases is caused by mutations of the ELANE gene,which encodes neutrophil elastase (NE). Recent data suggest a model in which ELANE mutations result in NE protein misfolding,induction of endoplasmic reticulum (ER) stress,activation of the unfolded protein response (UPR),and ultimately a block in granulocytic differentiation. To test this model,we generated transgenic mice carrying a targeted mutation of Elane (G193X) reproducing a mutation found in SCN. The G193X Elane allele produces a truncated NE protein that is rapidly degraded. Granulocytic precursors from G193X Elane mice,though without significant basal UPR activation,are sensitive to chemical induction of ER stress. Basal and stress granulopoiesis after myeloablative therapy are normal in these mice. Moreover,inaction of protein kinase RNA-like ER kinase (Perk),one of the major sensors of ER stress,either alone or in combination with G193X Elane,had no effect on basal granulopoiesis. However,inhibition of the ER-associated degradation (ERAD) pathway using a proteosome inhibitor resulted in marked neutropenia in G193X Elane. The selective sensitivity of G913X Elane granulocytic cells to ER stress provides new and strong support for the UPR model of disease patho-genesis in SCN. View Publication

Granulocyte colony-stimulating factor (G-CSF),the prototypical mobilizing cytokine,induces hematopoietic stem and progenitor cell (HSPC) mobilization from the bone marrow in a cell-nonautonomous fashion. This process is mediated,in part,through suppression of osteoblasts and disruption of CXCR4/CXCL12 signaling. The cellular targets of G-CSF that initiate the mobilization cascade have not been identified. We use mixed G-CSF receptor (G-CSFR)-deficient bone marrow chimeras to show that G-CSF-induced mobilization of HSPCs correlates poorly with the number of wild-type neutrophils. We generated transgenic mice in which expression of the G-CSFR is restricted to cells of the monocytic lineage. G-CSF-induced HSPC mobilization,osteoblast suppression,and inhibition of CXCL12 expression in the bone marrow of these transgenic mice are intact,demonstrating that G-CSFR signals in monocytic cells are sufficient to induce HSPC mobilization. Moreover,G-CSF treatment of wild-type mice is associated with marked loss of monocytic cells in the bone marrow. Finally,we show that bone marrow macrophages produce factors that support the growth and/or survival of osteoblasts in vitro. Together,these data suggest a model in which G-CSFR signals in bone marrow monocytic cells inhibit the production of trophic factors required for osteoblast lineage cell maintenance,ultimately leading to HSPC mobilization. View Publication

Polymorphonuclear neutrophils (PMNs) are critical for the formation,maintenance,and resolution of bacterial abscesses. However,the mechanisms that regulate PMN survival and proliferation during the evolution of an abscess are not well defined. Using a mouse model of Staphylococcus aureus abscess formation within a cutaneous wound,combined with real-time imaging of genetically tagged PMNs,we observed that a high bacterial burden elicited a sustained mobilization of PMNs from the bone marrow to the infected wound,where their lifespan was markedly extended. A continuous rise in wound PMN number,which was not accounted for by trafficking from the bone marrow or by prolonged survival,was correlated with the homing of c-kit(+)-progenitor cells from the blood to the wound,where they proliferated and formed mature PMNs. Furthermore,by blocking their recruitment with an antibody to c-kit,which severely limited the proliferation of mature PMNs in the wound and shortened mouse survival,we confirmed that progenitor cells are not only important contributors to PMN expansion in the wound,but are also functionally important for immune protection. We conclude that the abscess environment provides a niche capable of regulating PMN survival and local proliferation of bone marrow-derived c-kit(+)-progenitor cells. View Publication

The immune system is replenished by self-renewing hematopoietic stem cells (HSCs) that produce multipotent progenitors (MPPs) with little renewal capacity. E-proteins,the widely expressed basic helix-loop-helix transcription factors,contribute to HSC and MPP activity,but their specific functions remain undefined. Using quantitative in vivo and in vitro approaches,we show that E47 is dispensable for the short-term myeloid differentiation of HSCs but regulates their long-term capabilities. E47-deficient progenitors show competent myeloid production in short-term assays in vitro and in vivo. However,long-term myeloid and lymphoid differentiation is compromised because of a progressive loss of HSC self-renewal that is associated with diminished p21 expression and hyperproliferation. The activity of E47 is shown to be cell-intrinsic. Moreover,E47-deficient HSCs and MPPs have altered expression of genes associated with cellular energy metabolism,and the size of the MPP pool but not downstream lymphoid precursors in bone marrow or thymus is rescued in vivo by antioxidant. Together,these observations suggest a role for E47 in the tight control of HSC proliferation and energy metabolism,and demonstrate that E47 is not required for short-term myeloid differentiation. View Publication

P-selectin glycoprotein ligand-1 (PSGL-1) is a homodimeric transmembrane mucin on leukocytes. During inflammation,reversible interactions of PSGL-1 with selectins mediate leukocyte rolling on vascular surfaces. The transmembrane domain of PSGL-1 is required for dimerization,and the cytoplasmic domain propagates signals that activate β(2) integrins to slow rolling on integrin ligands. Leukocytes from knock-in ΔCD" mice express a truncated PSGL-1 that lacks the cytoplasmic domain. Unexpectedly� View Publication