Human hematopoietic reconstitution and HLA-restricted responses in nonpermissive alymphoid mice.

We generated a new humanized mouse model to study HLA-restricted immune responses. For this purpose, we created unique murine hosts by enforcing the expression of human SIRPα by murine phagocytes in murine MHC-deficient HLA-transgenic alymphoid hosts, an approach that allowed the immune reconstitution of nonpermissive mice following injection of human hematopoietic stem cells. We showed that these mouse/human chimeras were able to generate HLA-restricted responses to immunization. These new humanized mice may offer attractive models to study immune responses to human diseases, such as HIV and EBV infections, as well as to assay new vaccine strategies.

Fine mapping of the Bmgr5 quantitative trait locus for allogeneic bone marrow engraftment in mice.

To identify novel mechanisms regulating allogeneic hematopoietic cell engraftment, we used forward genetics and previously described identification, in mice, of a bone marrow (BM) engraftment quantitative trait locus (QTL), termed Bmgr5. This QTL confers dominant and large allele effects for engraftment susceptibility. It was localized to chromosome 16 by quantitative genetic techniques in a segregating backcross bred from susceptible BALB.K and resistant B10.BR mice. We now report verification of the Bmgr5 QTL using reciprocal chromosome 16 consomic strains. The BM engraftment phenotype in these consomic mice shows that Bmgr5 susceptibility alleles are not only sufficient but also indispensable for conferring permissiveness for allogeneic BM engraftment. Using panels of congenic mice, we resolved the Bmgr5 QTL into two separate subloci, termed Bmgr5a (Chr16:14.6-15.8 Mb) and Bmgr5b (Chr16:15.8-17.6 Mb), each conferring permissiveness for the engraftment phenotype and both fine mapped to an interval amenable to positional cloning. Candidate Bmgr5 genes were then prioritized using whole exome DNA sequencing and microarray gene expression data. Further studies are warranted to elucidate the genetic interaction between the Bmgr5a and Bmgr5b QTL and identify causative genes and underlying gene variants. This may lead to new approaches for overcoming the problem of graft rejection in clinical hematopoietic cell transplantation.

Rho-family GTPase Cdc42 controls migration of Langerhans cells in vivo.

Epidermal Langerhans cells (LCs) of the skin represent the prototype migratory dendritic cell (DC) subtype. In the skin, they take up Ag, migrate to the draining lymph nodes, and contribute to Ag transport and immunity. Different depletion models for LCs have revealed contrasting roles and contributions of this cell type. To target the migratory properties of DCs, we generated mice lacking the Rho-family GTPase Cdc42 specifically in DCs. In these animals, the initial seeding of the epidermis with LCs is functional, resulting in slightly reduced Langerhans cell numbers. However, Cdc42-deficient LCs fail to leave the skin in steady state as well as upon stimulation, as they do not enter the skin-draining afferent lymph vessels. Similarly, also other Cdc42-deficient migratory DC subsets fail to home properly to the corresponding draining lymph nodes. We used this novel mouse model, in which LCs are locked out, to demonstrate that these cells contribute substantially to priming of Ag-specific CD4 and CD8 T cell responses upon epicutaneous immunization, but could not detect a role in the induction of contact hypersensitivity to various doses of hapten.

FcγRIIb on myeloid cells and intrinsic renal cells rather than B cells protects from nephrotoxic nephritis.

FcγRIIb is the sole inhibitory FcR for IgG in humans and mice, where it is involved in the negative regulation of Ab production and cellular activation. FcγRIIb-deficient mice show exacerbated disease following the induction of nephrotoxic nephritis (NTN). In this study, we determined the cellular origin of the FcγRIIb-knockout phenotype by inducing NTN in mice with a deficiency of FcγRIIb on either B cells alone (FcγRIIB(fl/fl)/CD19Cre(+)) or myeloid cells (FcγRIIB(fl/fl)/CEBPαCre(+)). Deletion of FcγRIIb from B cells did not increase susceptibility to NTN, compared with wild-type (WT) mice, despite higher Ab titers in the FcγRIIB(fl/fl)/CD19Cre(+) mice compared with the WT littermate controls. In contrast, mice lacking FcγRIIb on myeloid cells had exacerbated disease as measured by increased glomerular thrombosis, glomerular crescents, albuminuria, serum urea, and glomerular neutrophil infiltration when compared with WT littermate controls. The role for FcγRIIb expression on radioresistant intrinsic renal cells in the protection from NTN was then investigated using bone marrow chimeric mice. FcγRIIb(-/-) mice transplanted with FcγRIIb(-/-) bone marrow were more susceptible to NTN than WT mice transplanted with FcγRIIb(-/-) bone marrow, indicating that the presence of WT intrinsic renal cells protects from NTN. These results demonstrate that FcγRIIb on myeloid cells plays a major role in protection from NTN, and therefore, augmentation of FcγRIIb on these cells could be a therapeutic target in human Ab-mediated glomerulonephritis. Where there was a lack of FcγRIIb on circulating myeloid cells, expression of FcγRIIb on intrinsic renal cells provided an additional level of protection from Ab-mediated glomerulonephritis.

Kainic acid-induced neuronal degeneration in hippocampal pyramidal neurons is driven by both intrinsic and extrinsic factors: analysis of FVB/N↔C57BL/6 chimeras.

The excitotoxic effects of kainic acid (KA) in the mouse hippocampus is strain dependent. Following KA administration, the large majority of hippocampal pyramidal cells die in the FVB/N (FVB) mouse, while the pyramidal cells of the C57BL/6 (B6) strain are largely spared. We generated aggregation chimeras between the sensitive FVB and the resistant B6 strains to investigate whether intrinsic or extrinsic features of a neuron confer cell vulnerability or resistance to KA. The constitutive expression of transgenic green fluorescence protein (GFP) or ß-galactosidase expressed from the ROSA26 locus was used to mark cells in FVB or B6 mice, respectively. These makers enable the identification of cells from each parental genotype while TUNEL (terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick end labeling)-staining labeled dying cells. The analysis of the percentage of dying cells in FVB-GFP ↔ B6-ROSA chimeras yielded an intriguing mix of both intrinsic and extrinsic factors in the readout of cell phenotype. Thus, normally resistant B6-ROSA pyramidal neurons demonstrated an increasing sensitivity to KA, in a linear fashion, when the percentage of FVB-GFP cells was increased, either across chimeras or in different regions of the same chimera. However, the death of B6-ROSA pyramidal cells never exceeded ∼70% of the total amount of B6 neurons regardless of the amount of FVB cells in the chimeric hippocampus. In a similar manner, FVB-GFP cells show lower amounts of cell death in chimeras that are colonized by B6-ROSA cells, but again, are never fully rescued. These data indicate that both intrinsic and extrinsic factors modulate the sensitivity of hippocampal pyramidal cells to kainic acid.

Subcongenic analyses reveal complex interactions between distal chromosome 4 genes controlling diabetogenic B cells and CD4 T cells in nonobese diabetic mice.

Autoimmune type 1 diabetes (T1D) in humans and NOD mice results from interactions between multiple susceptibility genes (termed Idd) located within and outside the MHC. Despite sharing ∼88% of their genome with NOD mice, including the H2(g7) MHC haplotype and other important Idd genes, the closely related nonobese resistant (NOR) strain fails to develop T1D because of resistance alleles in residual genomic regions derived from C57BLKS mice mapping to chromosomes (Chr.) 1, 2, and 4. We previously produced a NOD background strain with a greatly decreased incidence of T1D as the result of a NOR-derived 44.31-Mb congenic region on distal Chr. 4 containing disease-resistance alleles that decrease the pathogenic activity of autoreactive B and CD4 T cells. In this study, a series of subcongenic strains for the NOR-derived Chr. 4 region was used to significantly refine genetic loci regulating diabetogenic B and CD4 T cell activity. Analyses of these subcongenic strains revealed the presence of at least two NOR-origin T1D resistance genes within this region. A 6.22-Mb region between rs13477999 and D4Mit32, not previously known to contain a locus affecting T1D susceptibility and now designated Idd25, was found to contain the main NOR gene(s) dampening diabetogenic B cell activity, with Ephb2 and/or Padi2 being strong candidates as the causal variants. Penetrance of this Idd25 effect was influenced by genes in surrounding regions controlling B cell responsiveness and anergy induction. Conversely, the gene(s) controlling pathogenic CD4 T cell activity was mapped to a more proximal 24.26-Mb region between the rs3674285 and D4Mit203 markers.

B and T lymphocyte attenuator restricts the protective immune response against experimental malaria.

The immune response against the blood stage of malaria has to be tightly regulated to allow for vigorous antiplasmodial activity while restraining potentially lethal immunopathologic damage to the host like cerebral malaria. Coinhibitory cell surface receptors are important modulators of immune activation. B and T lymphocyte attenuator (BTLA) (CD272) is a coinhibitory receptor expressed by most leukocytes, with the highest expression levels on T and B cells, and is involved in the maintenance of peripheral tolerance by dampening the activation of lymphocytes. The function of BTLA is described in several models of inflammatory disorders and autoimmunity, but its function in infectious diseases is less well characterized. Also, little is known about the influence of BTLA on non-T cells. In this study, we analyzed the function of BTLA during blood-stage malaria infection with the nonlethal Plasmodium yoelii strain 17NL. We show that BTLA knockout mice exhibit strongly reduced parasitemia and clear the infection earlier compared with wild-type mice. This increased resistance was seen before the onset of adaptive immune mechanisms and even in the absence of T and B cells but was more pronounced at later time points when activation of T and B cells was observed. We demonstrate that BTLA regulates production of proinflammatory cytokines in a T cell-intrinsic way and B cell intrinsically regulates the production of P. yoelii 17NL-specific Abs. These results indicate that the coinhibitory receptor BTLA plays a critical role during experimental malaria and attenuates the innate as well as the subsequent adaptive immune response.

Impaired B cell development in the absence of Krüppel-like factor 3.

Krüppel-like factor 3 (Klf3) is a member of the Klf family of transcription factors. Klfs are widely expressed and have diverse roles in development and differentiation. In this study, we examine the function of Klf3 in B cell development by studying B lymphopoiesis in a Klf3 knockout mouse model. We show that B cell differentiation is significantly impaired in the bone marrow, spleen, and peritoneal cavity of Klf3 null mice and confirm that the defects are cell autonomous. In the bone marrow, there is a reduction in immature B cells, whereas recirculating mature cells are noticeably increased. Immunohistology of the spleen reveals a poorly structured marginal zone (MZ) that may in part be caused by deregulation of adhesion molecules on MZ B cells. In the peritoneal cavity, there are significant defects in B1 B cell development. We also report that the loss of Klf3 in MZ B cells is associated with reduced BCR signaling strength and an impaired ability to respond to LPS stimulation. Finally, we show increased expression of a number of Klf genes in Klf3 null B cells, suggesting that a Klf regulatory network may exist in B cells.

A role for autophagic protein beclin 1 early in lymphocyte development.

Autophagy is a highly regulated and evolutionarily conserved process of cellular self-digestion. Recent evidence suggests that this process plays an important role in regulating T cell homeostasis. In this study, we used Rag1(-/-) (recombination activating gene 1(-/-)) blastocyst complementation and in vitro embryonic stem cell differentiation to address the role of Beclin 1, one of the key autophagic proteins, in lymphocyte development. Beclin 1-deficient Rag1(-/-) chimeras displayed a dramatic reduction in thymic cellularity compared with control mice. Using embryonic stem cell differentiation in vitro, we found that the inability to maintain normal thymic cellularity is likely caused by impaired maintenance of thymocyte progenitors. Interestingly, despite drastically reduced thymocyte numbers, the peripheral T cell compartment of Beclin 1-deficient Rag1(-/-) chimeras is largely normal. Peripheral T cells displayed normal in vitro proliferation despite significantly reduced numbers of autophagosomes. In addition, these chimeras had greatly reduced numbers of early B cells in the bone marrow compared with controls. However, the peripheral B cell compartment was not dramatically impacted by Beclin 1 deficiency. Collectively, our results suggest that Beclin 1 is required for maintenance of undifferentiated/early lymphocyte progenitor populations. In contrast, Beclin 1 is largely dispensable for the initial generation and function of the peripheral T and B cell compartments. This indicates that normal lymphocyte development involves Beclin 1-dependent, early-stage and distinct, Beclin 1-independent, late-stage processes.

Lymphocyte development requires S-nitrosoglutathione reductase.

NO is critical to immunity, but its role in the development of the immune system is unknown. In this study, we show that S-nitrosoglutathione reductase (GSNOR), a protein key to the control of protein S-nitrosylation, is important for the development of lymphocytes. Genetic deletion of GSNOR in mice results in significant decrease in both T and B lymphocytes in the periphery. In thymus, GSNOR deficiency causes excessive protein S-nitrosylation, increases apoptosis, and reduces the number of CD4 single-positive thymocytes. Lymphopenia and increase in S-nitrosylation and apoptosis in GSNOR-deficient mice are largely abolished by genetic deletion of inducible NO synthase. Furthermore, the protection of lymphocyte development by GSNOR is apparently intrinsic to hematopoietic cells. Thus, GSNOR, likely through regulation of S-nitrosylation and apoptosis, physiologically plays a protective role in the development of the immune system.

A radiation hybrid map of the European sea bass (Dicentrarchus labrax) based on 1581 markers: Synteny analysis with model fish genomes.

The selective breeding of fish for aquaculture purposes requires the understanding of the genetic basis of traits such as growth, behaviour, resistance to pathogens and sex determinism. Access to well-developed genomic resources is a prerequisite to improve the knowledge of these traits. Having this aim in mind, a radiation hybrid (RH) panel of European sea bass (Dicentrarchus labrax) was constructed from splenocytes irradiated at 3000 rad, allowing the construction of a 1581 marker RH map. A total of 1440 gene markers providing ~4400 anchors with the genomes of three-spined stickleback, medaka, pufferfish and zebrafish, helped establish synteny relationships with these model species. The identification of Conserved Segments Ordered (CSO) between sea bass and model species allows the anticipation of the position of any sea bass gene from its location in model genomes. Synteny relationships between sea bass and gilthead seabream were addressed by mapping 37 orthologous markers. The sea bass genetic linkage map was integrated in the RH map through the mapping of 141 microsatellites. We are thus able to present the first complete gene map of sea bass. It will facilitate linkage studies and the identification of candidate genes and Quantitative Trait Loci (QTL). The RH map further positions sea bass as a genetic and evolutionary model of Perciformes and supports their ongoing aquaculture expansion.

ADAM17 activity and other mechanisms of soluble L-selectin production during death receptor-induced leukocyte apoptosis.

L-selectin is an adhesion molecule expressed by neutrophils that broadly directs their infiltration in to sites of inflammation. It is also present at relatively high levels in the serum of normal individuals. It is well established that L-selectin is efficiently shed from the surface of neutrophils upon their activation, a process that regulates its density and binding activity. Neutrophil programmed cell death is critical for the resolution of inflammation, and L-selectin downregulation is induced during this process as well. The mechanisms underpinning this latter process are much less understood, and were investigated in this study. Using a disintegrin and metalloprotease (ADAM)-17 radiation chimeric mice, we demonstrate for the first time that during early events of death receptor-mediated neutrophil apoptosis, L-selectin downregulation occurs primarily by ADAM17-mediated shedding. This was observed as well upon using shRNA to knock down ADAM17 expression in Jurkat cells, a well-studied cell line in terms of the molecular processes involved in the induction of apoptosis. These findings directly reveal that ADAM17 activity occurs during programmed cell death. Hence, the cleavage of particular ADAM17 substrates may be an additional component of the anti-inflammatory program initiated by apoptotic neutrophils. Of interest was that during later stages of induced leukocyte apoptosis, soluble L-selectin production occurred independent of ADAM17, as well as membrane events, such as blebbing and microparticle production. This process may provide an explanation for the lack of diminished serum L-selectin levels in ADAM17-null mice, and suggests a mechanism for the homeostatic maintenance of soluble L-selectin levels in the blood of healthy individuals.

On the longevity of resident endoneurial macrophages in the peripheral nervous system: a study of physiological macrophage turnover in bone marrow chimeric mice.

Macrophages are intimately involved in the pathogenesis of peripheral nervous system (PNS) disorders. Recently, we characterized a resident endoneurial macrophage population, which contributes rapidly to the endoneurial macrophage response in PNS diseases. Unlike microglial cells, resident macrophages undergo a physiological turnover of 50% in the sciatic nerve and 80% in dorsal root ganglia (DRG) within 12 weeks. Further information about the dynamics of this turnover is not available. This study examined the macrophage turnover in the sciatic nerve and DRGs over a longer period and addresses the question whether the turnover of resident macrophages is complete or whether there is a truly resident endoneurial macrophage population. We used chimeric mice carrying GFP(+) bone marrow and immunohistochemistry to detect hematogenous (GFP(+)) endoneurial macrophages after turnover. Non-exchanged, resident macrophages were GFP(-). Quantification of GFP(+) and GFP(-) macrophages revealed a maximal turnover of 75%, reached in DRGs after 12 weeks and in sciatic nerves after 36 weeks. GFP(-) long-term resident macrophages were further characterized after sciatic nerve injury, where they participated in the early macrophage response of Wallerian degeneration. Our results point toward a small but truly resident PNS macrophage population. These macrophages are an interesting target for further characterization and might have a distinct role in peripheral nerve disease.

Critical role of TLR9 in acute graft-versus-host disease.

Graft-vs-host disease (GVHD) is a major complication after allogeneic bone marrow transplantation. Different studies have demonstrated that intestinal bacterial breakdown products and loss of gastrointestinal tract integrity, both induced by conditioning regiments, are critical in the pathogenesis of acute GVHD. Using C57BL/6 knockout mice, we evaluated the role of TLR4 and TLR9, which recognize bacterial LPS and DNA, respectively, in the GVHD associated with allogeneic bone marrow transplantation. When myeloablative-irradiated TLR9 knockout (TLR9(-/-)) mice were used as graft recipients, survival and clinical score of acute GVHD were improved as compared with the wild-type recipient mice (18/30 vs 1/31 mice still alive at day 70 in a total of four experiments); while no differences were observed using recipient TLR4 knockout (TLR4(-/-)) mice. The reduced mortality and morbidity in TLR9(-/-) mice related with reduced stimulatory activity of TLR9(-/-) spleen APCs after conditioning and reduced proliferation of allogeneic donor T cells. Experiments using TLR9(+/+) into TLR9(-/-) and TLR9(-/-) into TLR9(+/+) chimeric mice as recipients indicated a critical role for nonhematopoietic TLR9(+/+) cells interacting with bacterial breakdown products released in myeloablated mice. Altogether these data reveal a novel important role of TLR9 in GVHD, a finding that might provide tools to reduce this complication of allogeneic transplantation.

Fibroblastic reticular cells guide T lymphocyte entry into and migration within the splenic T cell zone.

Although a great deal is known about T cell entry into lymph nodes, much less is understood about how T lymphocytes access the splenic white pulp (WP). We show in this study that, as recently described for lymph nodes, fibroblastic reticular cells (FRCs) form a network in the T cell zone (periarteriolar lymphoid sheath, PALS) of the WP on which T lymphocytes migrate. This network connects the PALS to the marginal zone (MZ), which is the initial site of lymphocyte entry from the blood. T cells do not enter the WP at random locations but instead traffic to that site using the FRC-rich MZ bridging channels (MZBCs). These data reveal that FRCs form a substrate for T cells in the spleen, guiding these lymphocytes from their site of entry in the MZ into the PALS, within which they continue to move on the same network.

Lentiviral-mediated transcriptional targeting of dendritic cells for induction of T cell tolerance in vivo.

Dendritic cells (DCs) are important APCs able to induce both tolerance and immunity. Therefore, DCs are attractive targets for immune intervention. However, the ex vivo generation and manipulation of DCs at sufficient numbers and without changing their original phenotypic and functional characteristics are major obstacles. To manipulate DCs in vivo, we developed a novel DC-specific self-inactivating lentiviral vector system using the 5' untranslated region from the DC-STAMP gene as a putative promoter region. We show that a gene therapy approach with these DC-STAMP-lentiviral vectors yields long-term and cell-selective transgene expression in vivo. Furthermore, transcriptionally targeted DCs induced functional, Ag-specific CD4 and CD8 T cell tolerance in vivo, which could not be broken by viral immunization. Tolerized CTL were unable to induce autoimmune diabetes in a murine autoimmune model system. Therefore, delivering transgenes specifically to DCs by using viral vectors might be a promising tool in gene therapy.

Cell intrinsic TGF-beta 1 regulation of B cells.

TGF-beta family cytokines play multiple roles in immune responses. TGF-beta1-null mice suffer from multi-organ infiltration that leads to their premature death. T cells play a central role in the TGF-beta1 phenotype, as deficiency of TGF-beta1 only in T cells reproduces the lethal phenotype. Although it is known that TGF-beta1 controls B cells isotype switch and homeostasis, the source responsible for this control has not been characterized. Because of the major role that T cells play in regulating B cell responses, we addressed the T cell dependency of the TGF-beta1 control of B cells. The analysis of T cell-deficient, TGF-beta1 knockout mice and the production of chimeras in which B but not T cells lacked TGF-beta1 allowed us to show that B cells are controlled in part by cell autonomous production of TGF-beta1.

Blood monocyte subsets differentially give rise to CD103+ and CD103- pulmonary dendritic cell populations.

There are two major myeloid pulmonary dendritic cell (DC) populations: CD103+ DCs and CD11bhigh DCs. In this study, we investigated in detail the origins of both myeloid DC pools using multiple experimental approaches. We show that, in resting lung, Ly-6ChighCCR2high monocytes repopulated CD103+ DCs using a CCR2-dependent mechanism, and these DCs preferentially retained residual CCR2 in the lung, whereas, conversely, Ly-6ClowCCR2low monocytes repopulated CD11bhigh DCs. CX3CR1 was required to generate normal numbers of pulmonary CD11bhigh DCs, possibly because Ly-6Clow monocytes in the circulation, which normally express high levels of CX3CR1, failed to express bcl-2 and may have diminished survival in the circulation in the absence of CX3CR1. Overall, these data demonstrate that the two circulating subsets of monocytes give rise to distinct tissue DC populations.

Identification of a radio-resistant and cycling dermal dendritic cell population in mice and men.

In this study, we explored dermal dendritic cell (DC) homeostasis in mice and humans both in the steady state and after hematopoietic cell transplantation. We discovered that dermal DCs proliferate in situ in mice and human quiescent dermis. In parabiotic mice with separate organs but shared blood circulation, the majority of dermal DCs failed to be replaced by circulating precursors for >6 mo. In lethally irradiated mice injected with donor congenic bone marrow (BM) cells, a subset of recipient DCs remained in the dermis and proliferated locally throughout life. Consistent with these findings, a large proportion of recipient dermal DCs remained in patients' skin after allogeneic hematopoietic cell transplantation, despite complete donor BM chimerism. Collectively, our results oppose the traditional view that DCs are nondividing terminally differentiated cells maintained by circulating precursors and support the new paradigm that tissue DCs have local proliferative properties that control their homeostasis in the steady state. Given the role of residual host tissue DCs in transplant immune reactions, these results suggest that dermal DC homeostasis may contribute to the development of cutaneous graft-versus-host disease in clinical transplantation.