Innate and adaptive immunity: the understudied driving force of heart valve disease.

Calcific aortic valve disease (CAVD), and its clinical manifestation that is calcific aortic valve stenosis, is the leading cause for valve disease within the developed world, with no current pharmacological treatment available to delay or halt its progression. Characterized by progressive fibrotic remodelling and subsequent pathogenic mineralization of the valve leaflets, valve disease affects 2.5% of the western population, thus highlighting the need for urgent intervention. Whilst the pathobiology of valve disease is complex, involving genetic factors, lipid infiltration, and oxidative damage, the immune system is now being accepted to play a crucial role in pathogenesis and disease continuation. No longer considered a passive degenerative disease, CAVD is understood to be an active inflammatory process, involving a multitude of pro-inflammatory mechanisms, with both the adaptive and the innate immune system underpinning these complex mechanisms. Within the valve, 15% of cells evolve from haemopoietic origin, and this number greatly expands following inflammation, as macrophages, T lymphocytes, B lymphocytes, and innate immune cells infiltrate the valve, promoting further inflammation. Whether chronic immune infiltration or pathogenic clonal expansion of immune cells within the valve or a combination of the two is responsible for disease progression, it is clear that greater understanding of the immune systems role in valve disease is required to inform future treatment strategies for control of CAVD development.

CqPP2A inhibits white spot syndrome virus infection by up-regulating antimicrobial substances expression in red claw crayfish Cherax quadricarinatus.

Protein phosphatase 2A (PP2A) is an important serine/threonine phosphatase, a highly conserved enzyme widely expressed in eukaryotic cells, which accounts for a majority of the serine/threonine phosphatase activity in cells implicated in regulation of immune signaling pathways and antiviral response. However, most of studies about PP2A have been conducted in mammals but few in crustaceans. In this study, two subunits of PP2A (named as CqPP2Ab and CqPP2Ac) were characterized to be involved in white spot syndrome virus (WSSV) infection in the haematopoietic tissue (Hpt) cells from red claw crayfish Cherax quadricarinatus. The open reading frame (ORF) of CqPP2Ab was 1341 bp encoding 446 amino acids with seven WD40 domains, and the ORF of CqPP2Ac was 930 bp encoding 309 amino acids with a PP2Ac domain. Tissue distribution analysis showed that the mRNA transcript of CqPP2Ab and CqPP2Ac were both widely expressed in all the tested tissues with the highest expression in hemocyte, followed by high expression in Hpt. The gene expressions of CqPP2Ab and CqPP2Ac were both significantly down-regulated at 6 h post WSSV infection (6 hpi) in Hpt cells. Importantly, the expression of viral immediate early gene IE1 and late viral gene envelope protein VP28 were both significantly increased post WSSV infection after gene silencing of CqPP2Ab or CqPP2Ac in Hpt cells, suggesting that CqPP2Ab and CqPP2Ac could inhibit WSSV infection in Hpt cells, probably by increasing the antimicrobial substances expression in consideration to the significantly reduced expression of anti-lipopolysaccharide factor, crustin, and lysozyme after gene silencing of CqPP2Ab or CqPP2Ac, respectively. These findings provide a new light on the mechanism of WSSV infection and the antiviral response in crustaceans.

Immunopathogenesis of hematopoietic tissues in response to Vibrio parahaemolyticus (VPAHPND) infection in Macrobrachium rosenbergii.

In crustacean, hemocytes are known as crucial components of crustaceans' innate immunity against pathogens. Drastic hemocytes reduction during infectious disease is apparently related to disease severity and calls for a health status evaluation and aquaculture management. The molecular pathogenesis of hemocytes loss during bacterial infection was elucidated with VPAHPND challenged in M. rosenbergii. We report herein a correlation between hemocyte loss and the pathogenicity and aggressive immune response in hematopoietic tissues of moribund M. rosenbergii. In this study, adult freshwater prawn was administered an LC50 dose of VPAHPND; bacterial clearance ensued, and success was reached within 24 h. Hemocytes increased in survival, yet drastically decreased in moribund prawn. Pathological analysis of hematopoietic tissue of moribund prawn showed apparent abnormal signs, including the presence of bacteria, a small number of mitotic cells, cellular swelling, loosening of connective tissue, and karyorrhectic nuclei cells. A significant upregulation of a core apoptotic machinery gene, caspase-3, was detected in hematopoietic tissue of moribund shrimp, but not in those of Escherichia coli DH5α (non-pathogenic bacteria) and VPAHPND survival prawn. The highest level was found in the moribund group, which confirms the occurrence of apoptosis in this hematopoietic tissue. Further, our results suggest that hematopoietic tissue damage may arise from inflammation triggered by an aggressive immune response. Immune activation was indicated by the comparison of immune-related gene expression between controls, E. coli (DH5α)-infected (non-pathogenic), and VPAHPND-infected survival groups with moribund prawn. RT-PCR revealed a significant upregulation of all genes in hematopoietic tissues and hemocytes within 6-12 h and declined by 24 h. This evident related to the almost VPAHPND are clearance in survival and E. coli (DH5α) challenged group in contrast with drastic high expression was determined in moribund group. We conclude that a reduction of renewing circulating hemocytes in fatally VPAHPND-infected prawn was caused by an acute self-destructive immune response by hematopoietic cells.

Immune Reconstitution and Thymic Involution in the Acute and Delayed Hematopoietic Radiation Syndromes.

Lymphoid lineage recovery and involution after exposure to potentially lethal doses of ionizing radiation have not been well defined, especially the long-term effects in aged survivors and with regard to male/female differences. To examine these questions, male and female C57BL/6 mice were exposed to lethal radiation at 12 wk of age in a model of the Hematopoietic-Acute Radiation Syndrome, and bone marrow, thymus, spleen, and peripheral blood examined up to 24 mo of age for the lymphopoietic delayed effects of acute radiation exposure. Aged mice showed myeloid skewing and incomplete lymphocyte recovery in all lymphoid tissues. Spleen and peripheral blood both exhibited a monophasic recovery pattern, while thymus demonstrated a biphasic pattern. Naïve T cells in blood and spleen and all subsets of thymocytes were decreased in aged irradiated mice compared to age-matched non-irradiated controls. Of interest, irradiated males experienced significantly improved reconstitution of thymocyte subsets and peripheral blood elements compared to females. Bone marrow from aged irradiated survivors was significantly deficient in the primitive lymphoid-primed multipotent progenitors and common lymphoid progenitors, which were only 8-10% of levels in aged-matched non-irradiated controls. Taken together, these analyses define significant age- and sex-related deficiencies at all levels of lymphopoiesis throughout the lifespan of survivors of the Hematopoietic-Acute Radiation Syndrome and may provide a murine model suitable for assessing the efficacy of potential medical countermeasures and therapeutic strategies to alleviate the severe immune suppression that occurs after radiation exposure.

Characterization of immune response against Mycobacterium marinum infection in the main hematopoietic organ of adult zebrafish (Danio rerio).

Tuberculosis remains a major global health challenge. To gain information about genes important for defense against tuberculosis, we used a well-established tuberculosis model; Mycobacterium marinum infection in adult zebrafish. To characterize the immunological response to mycobacterial infection at 14 days post infection, we performed a whole-genome level transcriptome analysis using cells from kidney, the main hematopoietic organ of adult zebrafish. Among the upregulated genes, those associated with immune signaling and regulation formed the largest category, whereas the largest group of downregulated genes had a metabolic role. We also performed a forward genetic screen in adult zebrafish and identified a fish line with severely impaired survival during chronic mycobacterial infection. Based on transcriptome analysis, these fish have decreased expression of several immunological genes. Taken together, these results give new information about the genes involved in the defense against mycobacterial infection in zebrafish.

The hematopoietic organ of Macrobrachium rosenbergii: Structure, organization and immune status.

The hematopoietic organ (HO) of the giant freshwater prawn Macrobrachium rosenbergii is a discrete, whitish mass located in the epigastric region of the cephalothorax, posterior to the brain. It is composed of hematopoietic cells arranged in a thick layer of numerous lobules that surround a central hemal sinus from which they are separated by a thin sheath. At the center of the sinus is the muscular cor frontale. The lobules extend radially outward from the sinus in three developmental zones. Basal Zone 1 nearest the sinus contains large hematopoietic stem cells with euchromatic nuclei that stain positive for proliferation cell nuclear antigen (PCNA). Zone 2 contains smaller, actively dividing cells as indicated by positive 5-bromo-20-deoxyuridine (BrdU) staining. Distal Zone 3 contains small, loosely packed cells with heterochromatic nuclei, many cytoplasmic granules and vesicles indicating that they will eventually differentiate into hemocytes and enter circulation. Three main arteries, namely the ophthalmic and the 2 branches of the antennary, connect the heart to the HO. Use of India ink and 0.1 µm fluorescent micro-beads injected into the heart revealed that the cor frontale could immediately remove foreign particles from hemolymph by filtration. Fluorescent beads were also detected in the hematopoietic tissue at 30 min after injection, indicating that it could be penetrated by foreign particles. However, the fluorescent signal completely disappeared from the whole HO after 4 h, indicating its role in removal of foreign particles. In conclusion, the present study demonstrated for the first time the detailed histological structures of the HO of M. rosenbergii and its relationship to hematopoiesis and removal of foreign particles from hemolymph.

A multicenter study of patients with multisystem Langerhans cell histiocytosis who develop secondary hemophagocytic lymphohistiocytosis.

BACKGROUND: Langerhans cell histiocytosis (LCH) is a rare myeloid neoplasm characterized by the presence of abnormal CD1a-positive (CD1a+ )/CD207+ histiocytes. Hemophagocytic lymphohistiocytosis (HLH) represents a spectrum of hyperinflammatory syndromes typified by the dysregulated activation of the innate and adaptive immune systems. Patients with LCH, particularly those with multisystem (MS) involvement, can develop severe hyperinflammation mimicking that observed in HLH. Nevertheless, to the authors' knowledge, little is known regarding the prevalence, timing, risk factors for development, and outcomes of children and young adults who develop HLH within the context of MS-LCH (hereafter referred to LCH-associated HLH). METHODS: To gain further insights, the authors conducted a retrospective, multicenter study and collected data regarding all patients diagnosed with MS-LCH between 2000 and 2015. RESULTS: Of 384 patients with MS-LCH, 32 were reported by their primary providers to have met the diagnostic criteria for HLH, yielding an estimated 2-year cumulative incidence of 9.3% ± 1.6%. The majority of patients developed HLH at or after the diagnosis of MS-LCH, and nearly one-third (31%) had evidence of an intercurrent infection. Patient age <2 years at the time of diagnosis of LCH; female sex; LCH involvement of the liver, spleen, and hematopoietic system; and a lack of bone involvement each were found to be independently associated with an increased risk of LCH-associated HLH. Patients with MS-LCH who met the criteria for HLH had significantly poorer 5-year survival compared with patients with MS-LCH who did not meet the criteria for HLH (69% vs 97%; P < .0001). CONCLUSIONS: Given its inferior prognosis, further efforts are warranted to enhance the recognition and optimize the treatment of patients with LCH-associated HLH.

Transfection of crayfish hematopoietic tissue cells.

Transfection is a powerful tool useful for studying gene function. Establishing transfection methods that enable highly efficient DNA uptake has become increasingly important. The crayfish hematopoietic tissue (Hpt) cell cultures have been proven to be suitable for studies on immunity and cell differentiation in crustaceans including shrimps, but no efficient gene transfer and expression method is available for these cells. Here we report a novel and highly efficient DNA transfection system based on electroporation. This method depends on a recombinant plasmid with the promoter from white spot syndrome virus immediate-early gene wsv249. This plasmid could be introduced into primary cells and efficiently express foreign genes by electroporation. By optimizing different electroporation parameters, more than 30% transfection efficiency could be achieved with the relative viability of cells around 50%. This is the first report of gene introduction to crayfish Hpt cells and will be useful for the expanding our research on crustacean immunity.

Donor and recipient age, gender and ABO incompatibility regardless of donor source: validated criteria for donor selection for haematopoietic transplants.

Prior data indicate similar outcomes after transplants from human leukocyte antigen (HLA)-haplotype-matched relatives, HLA-identical siblings and HLA-matched unrelated donors. We used our prospective data set to answer a clinically important question: who is the best donor for a person with acute leukaemia transplanted in first complete remission. Patients were randomly divided into training (n=611) and validation (n=588) sets. A total of 1199 consecutive subjects received a transplant from an HLA-haplotype-matched relative using granulocyte colony-stimulating factor and anti-thymocyte globulin (n=685) or an HLA-identical sibling (n=514); 3-year leukaemia-free survivals (LFSs) were 75 and 74% (P=0.95), respectively. The multivariate model identified three major risk factors for transplant-related mortality (TRM): older donor/recipient age, female-to-male transplants and donor-recipient ABO major-mismatch transplants. A risk score was developed based on these three features. TRMs were 8%, 15% and 31% for subjects with scores of 0-1, 2 and 3, respectively, (P<0.001). Three-year LFSs were 78%, 74% and 58%, respectively, (P=0.003). The risk score was validated in an independent cohort. In conclusion, our data confirm donor source is not significantly correlated with transplant outcomes. Selection of the best donor needs to consider donor-recipient age, matching for gender and ABO incompatibility among persons with acute leukaemia receiving related transplants under our transplant modality.

Distinctive Leukocyte Subpopulations According to Organ Type in Cynomolgus Macaques.

Cynomolgus macaques (CYNO; Macaca fascicularis) are a well-established NHP model used for studies in immunology. To provide reference values on the baseline cell distributions in the hematopoietic and lymphoid organs (HLO) of these animals, we used flow cytometry to analyze the peripheral blood, bone marrow, mesenteric lymph nodes, spleen, and thymus of a cohort of male, adult, research-naïve, Mauritian CYNO. Our findings demonstrate that several cell distribution patterns differ between CYNO and humans. First, the CD4(+):CD8(+) T-cell ratio is lower in CYNO compared with humans. Second, the peripheral blood of CYNO contains a population of CD4(+)CD8(+) T cells. Third, the CD31 level was elevated in all organs studied, suggesting that CD31 may not be an accurate marker of recent thymic emigrants within the CD4(+) T cells of CYNO. Finally the B-cell population is lower in CYNO compared with humans. In summary, although the majority of immune cell populations are similar between cynomolgus macaques and humans, several important differences should be considered when using CYNO in immunologic studies. Our current findings provide valuable information to not only researchers but also veterinarians working with CYNO at research centers, in zoos, or in the wild.

Proteomic analysis by iTRAQ in red claw crayfish, Cherax quadricarinatus, hematopoietic tissue cells post white spot syndrome virus infection.

To elucidate proteomic changes of Hpt cells from red claw crayfish, Cherax quadricarinatus, we have carried out isobaric tags for relative and absolute quantitation (iTRAQ) of cellular proteins at both early (1 hpi) and late stage (12 hpi) post white spot syndrome virus (WSSV) infection. Protein database search revealed 594 protein hits by Mascot, in which 17 and 30 proteins were present as differentially expressed proteins at early and late viral infection, respectively. Generally, these differentially expressed proteins include: 1) the metabolic process related proteins in glycolysis and glucogenesis, DNA replication, nucleotide/amino acid/fatty acid metabolism and protein biosynthesis; 2) the signal transduction related proteins like small GTPases, G-protein-alpha stimulatory subunit, proteins bearing PDZ- or 14-3-3-domains that help holding together and organize signaling complexes, casein kinase I and proteins of the MAP-kinase signal transduction pathway; 3) the immune defense related proteins such as α-2 macroglobulin, transglutaminase and trans-activation response RNA-binding protein 1. Taken together, these protein information shed new light on the host cellular response against WSSV infection in a crustacean cell culture.

Humanized hemato-lymphoid system mice.

Over the last decades, incrementally improved xenograft mouse models, supporting the engraftment and development of a human hemato-lymphoid system, have been developed and now represent an important research tool in the field. The most significant contributions made by means of humanized mice are the identification of normal and leukemic hematopoietic stem cells, the characterization of the human hematopoietic hierarchy, and their use as preclinical therapy models for malignant hematopoietic disorders. Successful xenotransplantation depends on three major factors: tolerance by the mouse host, correct spatial location, and appropriately cross-reactive support and interaction factors such as cytokines and major histocompatibility complex molecules. Each of these can be modified. Experimental approaches include the genetic modification of mice to faithfully express human support factors as non-cross-reactive cytokines, to create free niche space, the co-transplantation of human mesenchymal stem cells, the implantation of humanized ossicles or other stroma, and the implantation of human thymic tissue. Besides the source of hematopoietic cells, the conditioning regimen and the route of transplantation also significantly affect human hematopoietic development in vivo. We review here the achievements, most recent developments, and the remaining challenges in the generation of pre-clinically-predictive systems for human hematology and immunology, closely resembling the human situation in a xenogeneic mouse environment.

Locust cellular defense against infections: sites of pathogen clearance and hemocyte proliferation.

The locust cellular defense is mediated by hemocytes and hematopoietic tissue. In Locusta migratoria, the hemocytes and hematopoietic tissue mutually assist each other in clearing invading pathogens from circulation. A ß-1, 3-glucan infection induces nodule formation and apoptotic, TUNEL positive, cells in the hematopoietic tissue and massive loss of hemocytes in the circulation, calling for instant proliferation of hemocytes and hematopoietic tissue cells to assure continued host cellular defense. As the locust hematopoietic tissue persists at the adult stage, it was originally designated as being the major source for the replenishment process. Revisiting post infection hemocyte proliferation, using immunofluorescence based tests for DNA synthesis and mitosis, evidenced the lack of ß-1, 3-glucan induced cell proliferation in the hematopoietic tissue. Instead these tests identified the circulating hemocytes as the major source for hemocyte replenishment in the circulation. The hematopoietic tissue, however, undergoes a continuous, slow and infection independent regeneration, thereby accumulating potential phagocytes despite infection, and might serve a prophylactic role in containing pathogens in this swarming insect.

[Anti-mouse CD122 antibody promotes the hematopoietic repopulating capacity of cord blood CD34⁺ cells in NOD/SCID mice].

The study was aimed to investigate the effect of anti-mouse CD122 antibody on the hematopoietic repopulating capacity of cord blood CD34⁺ cells in a humanized murine model-non obese diabetic/severe combined immunodeficiency (NOD/SCID) mice. After sublethal irradiation with γ-ray, NOD/SCID mice were intraperitoneally injected with 200 µg mouse isotype control antibody or anti-mouse CD122 antibody. Human cord blood CD34⁺ cells or phosphate-buffered saline (PBS) were injected via the tail vein at 6-8 hours later. Cohort of the mice injected with anti-mice CD122 antibody or control antibody alone were sacrificed at different time point (at week 2, 3, and 4 weeks) after the injection, and the percentage of NK cells in the peripheral blood was analyzed by flow cytometry. To evaluate the effect of anti-mouse CD122 antibody on the repopulating capacity of cord blood CD34⁺ cells in the recipient mice, phenotype analysis was performed in the bone marrow at 6 and 8 weeks after the transplantation. The results showed that the proportion of NK cells in the peripheral blood were (4.6 ± 0.6)% and (5.7 ± 1.7)% at week 2 and 3 after anti-CD122 antibody injection respectively,which decreased by 60%, compared with the mice injected with isotype control antibody. After 6 and 8 weeks of cord blood CD34⁺ cell transplantation,the percentage of human CD45⁺ in the bone marrow of the recipient mice treated with anti-mice CD122 antibody was (63.0 ± 12.2)% and (53.2 ± 16.3)%,respectively,which were dramatically higher than that in the mice treated with isotype control antibody (7.7 ± 3.6)% and (6.1 ± 2.4)%. Moreover,at 8 weeks after transplantation,human CD34⁺ cells appeared significantly in the recipients treated with anti-CD122 antibody. It is concluded that the anti-mouse CD122 antibody enhances the hematopoietic repopulating capacity of cord blood CD34⁺ cells in the NOD/SCID mice through decreasing the proportion of NK cells.

Role of major histocompatibility complex class II expression by non-hematopoietic cells in autoimmune and inflammatory disorders: facts and fiction.

It is well established that interactions between CD4(+) T cells and major histocompatibility complex class II (MHCII) positive antigen-presenting cells (APCs) of hematopoietic origin play key roles in both the maintenance of tolerance and the initiation and development of autoimmune and inflammatory disorders. In sharp contrast, despite nearly three decades of intensive research, the functional relevance of MHCII expression by non-hematopoietic tissue-resident cells has remained obscure. The widespread assumption that MHCII expression by non-hematopoietic APCs has an impact on autoimmune and inflammatory diseases has in most instances neither been confirmed nor excluded by indisputable in vivo data. Here we review and put into perspective conflicting in vitro and in vivo results on the putative impact of MHCII expression by non-hematopoietic APCs--in both target organs and secondary lymphoid tissues--on the initiation and development of representative autoimmune and inflammatory disorders. Emphasis will be placed on the lacunar status of our knowledge in this field. We also discuss new mouse models--developed on the basis of our understanding of the molecular mechanisms that regulate MHCII expression--that constitute valuable tools for filling the severe gaps in our knowledge on the functions of non-hematopoietic APCs in inflammatory conditions.

Function of junctional adhesion molecules (JAMs) in leukocyte migration and homeostasis.

Homeostasis is a word widely used in the scientific community to refer to the property of a system to maintain its uniformity and functionality. In living organisms, the word refers to the concept enunciated 150 years ago by C. Bernard by which external variations must be compensated for in order to maintain internal conditions compatible with life. This is especially true in the case of highly dynamic system such as the hematopoietic system that requires the coordinated control of cell proliferation and death within specialized microenvironments that are anatomically distinct. As a consequence, hematopoietic cell adhesion and migration must be tightly controlled in order for hematopoietic cells to reach and to be maintained in appropriate microenvironments. The junctional adhesion molecules (JAMs) are adhesion molecules that belong to the immunoglobulin superfamily (IgSf) and that have been initially identified as important players controlling vascular permeability and leukocyte transendothelial migration. This involves the regulated localization of the JAMs at lateral endothelial cell/cell borders and their interaction with leukocyte integrins. More recently, some of the JAM family members have also been found to be expressed by stromal cells and to regulate chemokine secretion within lymphoid organs, acting not only on leukocyte transendothelial migration, but also on hematopoietic cell retention within specialized microenvironments. This review summarizes recent progress in understanding the role of the JAMs in leukocyte adhesion and migration to tentatively draw an integrated view of the homeostatic function of the JAMs within the hematopoietic system.

Differentiation of rodent immune and hematopoietic system reactive lesions from neoplasias.

The immune and hematopoietic systems play an important role in the normal homeostasis of blood and blood cells and for immune responses to endogenous and exogenous processes and insults. In order to interpret histopathologic changes in the immune and hematopoietic systems, it is important to understand the normal anatomy and histology of the thymus, spleen, lymph nodes, bone marrow, and other tissues. The thymus, spleen, and lymph nodes can be categorized by anatomical compartments, each of which contributes to specific immune functions. Lesions may be diagnosed by interpretive or descriptive (semiquantitative) methods. The interpretation of these tissues by lesion in anatomical compartments should allow for better understanding of these reactions and more definitive pathologic findings. Proliferative lesions may be difficult to differentiate from lymphomas and leukemias. The use of immunohistochemistry, compartmental pathology, and methods for the evaluation of clonality will make interpretation easier.

3D co-culture of hematopoietic stem and progenitor cells and mesenchymal stem cells in collagen scaffolds as a model of the hematopoietic niche.

Here, we propose a collagen-based three-dimensional (3D) environment for hematopoietic stem and progenitor cells (HPC) with mesenchymal stem cells (MSC) derived either from bone marrow (BM) or umbilical cord (UC), to recapitulate the main components of the BM niche. Mechanisms described for HPC homeostasis were systematically analyzed in comparison to the conventional liquid HPC culture. The 3D-cultivation allows dissecting two sub-populations of HPC: (I) HPC in suspension above the collagen gel and (II) migratory HPC in the collagen fibres of the collagen gel. The different sites represent distinct microenvironments with significant impact on HPC fate. HPC in niche I (suspension) are proliferative and a dynamic culture containing HPC (CD34(+)/CD38(-)), maturing myeloid cells (CD38(+), CD13(+), CAE(+)) and natural killer (NK) cells (CD56(+)). In contrast, HPC in niche II showed clonal growth with significant high levels of the primitive CD34(+)/CD38(-) phenotype with starting myeloid (CD13(+), CAE(+)) differentiation, resembling the endosteal part of the BM niche. In contrast, UC-MSC are not adequate for HSC expansion as they significantly enhance HPC proliferation and lineage commitment. In conclusion, the 3D-culture system using collagen and BM-MSC enables HPC expansion and provides a potential platform to dissect regulatory mechanisms in hematopoiesis.

Recipient nonhematopoietic antigen-presenting cells are sufficient to induce lethal acute graft-versus-host disease.

The presentation pathways by which allogeneic peptides induce graft-versus-host disease (GVHD) are unclear. We developed a bone marrow transplant (BMT) system in mice whereby presentation of a processed recipient peptide within major histocompatibility complex (MHC) class II molecules could be spatially and temporally quantified. Whereas donor antigen presenting cells (APCs) could induce lethal acute GVHD via MHC class II, recipient APCs were 100-1,000 times more potent in this regard. After myeloablative irradiation, T cell activation and memory differentiation occurred in lymphoid organs independently of alloantigen. Unexpectedly, professional hematopoietic-derived recipient APCs within lymphoid organs had only a limited capacity to induce GVHD, and dendritic cells were not required. In contrast, nonhematopoietic recipient APCs within target organs induced universal GVHD mortality and promoted marked alloreactive donor T cell expansion within the gastrointestinal tract and inflammatory cytokine generation. These data challenge current paradigms, suggesting that experimental lethal acute GVHD can be induced by nonhematopoietic recipient APCs.

Expansion of a restricted residual host T reg-cell repertoire is dependent on IL-2 following experimental autologous hematopoietic stem transplantation.

We previously identified a population of residual T(reg) cells following autologous hematopoietic stem transplantation (HSCT), that rapidly undergoes significant expansion in lymphopenic transplant recipients prior to repopulation by donor de novo derived T(reg) cells. These CD4(+) Foxp3(+) T cells provide protection from the development of autoimmune disease. Although ablative conditioning results in excess IL-7 and IL-15, IL-2 is typically not found at high levels following autologous HSCT. We therefore examined the role of these three STAT-5 signaling cytokines in the expansion of residual T(reg) cells after autologous HSCT. The present study found that the residual T(reg) cell population included surviving peripheral host Foxp3(+) CD4(+) T cells whose expansion was critically dependent on IL-2, which could be solely provided by surviving host cells. IL-7 was found to contribute to T(reg) cell homeostasis, however, not as a growth factor but rather for their persistence. In conjunction with this expansion, TCR spectratype analyses revealed that the residual host T(reg) -cell compartment differed from that present in non-conditioned healthy mice since the residual host Treg cells exhibit a limited TCR diversity. Collectively, these data indicate that the proliferation of T(reg) and T effector (T(eff) ) cells post-HSCT utilize separate pools of cytokines which has important implications regarding the development of clinical strategies to elicit the desired immune responses in patients post-transplant.