Fibroblasts from human spleen regulate NK cell differentiation from blood CD34(+) progenitors via cell surface IL-15

Plasmodium vivax tryptophan-rich antigen reduces type I collagen secretion via the NF-κBp65 pathway in splenic fibroblasts

BACKGROUND

The spleen plays a critical role in the immune response against malaria parasite infection, where splenic fibroblasts (SFs) are abundantly present and contribute to immune function by secreting type I collagen (collagen I). The protein family is characterized by Plasmodium vivax tryptophan-rich antigens (PvTRAgs), comprising 40 members. PvTRAg23 has been reported to bind to human SFs (HSFs) and affect collagen I levels. Given the role of type I collagen in splenic immune function, it is important to investigate the functions of the other members within the PvTRAg protein family.

METHODS

Protein structural prediction was conducted utilizing bioinformatics analysis tools and software. A total of 23 PvTRAgs were successfully expressed and purified using an Escherichia coli prokaryotic expression system, and the purified proteins were used for co-culture with HSFs. The collagen I levels and collagen-related signaling pathway protein levels were detected by immunoblotting, and the relative expression levels of inflammatory factors were determined by quantitative real-time PCR.

RESULTS

In silico analysis showed that P. vivax has 40 genes encoding the TRAg family. The C-terminal region of all PvTRAgs is characterized by the presence of a domain rich in tryptophan residues. A total of 23 recombinant PvTRAgs were successfully expressed and purified. Only five PvTRAgs (PvTRAg5, PvTRAg16, PvTRAg23, PvTRAg30, and PvTRAg32) mediated the activation of the NF-κBp65 signaling pathway, which resulted in the production of inflammatory molecules and ultimately a significant reduction in collagen I levels in HSFs.

CONCLUSIONS

Our research contributes to the expansion of knowledge regarding the functional role of PvTRAgs, while it also enhances our understanding of the immune evasion mechanisms utilized by parasites.

Case report: Single-cell mapping of peripheral blood mononuclear cells from a patient with both Crohn’s disease and isolated congenital asplenia

Crohn’s disease (CD), as one of the principal form of inflammatory bowel disease (IBD), is characterized by the chronic and recurring inflammatory conditions in the intestine resulting from the over-activation of intestinal immunity. Hyposplenism is strongly associated with CD, while the effect of human spleen on the differentiation and development of immune cell subsets in CD patients remains unclear. Isolated congenital asplenia (ICA) is an extremely rare condition characterized by the absence of a spleen at birth without any other developmental defects. Here, we describe the first case of a patient with both ICA and CD, and follow the progression of CD from remission to active stage. Using cytometry by time of flight (CyTOF) analysis, we draw the first single-cell mapping of peripheral blood mononuclear cells (PBMC) from this unique patient, tracing back to the innate or adaptive immune cell subsets and cell surface markers affected by the spleen. Based on our analysis, it is speculated that the spleen contributes to maintaining immune homeostasis, alleviating intestinal inflammation and improving prognosis by influencing the differentiation and development of peripheral immune cell subsets and the expression of cell surface markers in patients with CD.

Overcoming the UCB HSCs -Derived NK cells Dysfunction through Harnessing RAS/MAPK, IGF-1R and TGF-β Signaling Pathways

Background

The natural killer (NK) cells differentiated from umbilical cord blood (UCB) hematopoietic stem cells (HSCs) may be more suitable for cell-based immunotherapy compared to the NK cells from adult donors. This is due to the possibility to choose alloreactive donors and potentially more robust in vivo expansion. However, the cytotoxicity of UCB-HSC-derived NK cells against cancer cells might be suboptimal. To overcome this obstacle, we attempted to generate NK cells with potent antitumor activity by targeting RAS/MAPK, IGF-1R and TGF-β signaling pathways using IL-15, IGF-1 and SIS3 respectively.

Methods

The CD34 + cells were isolated from human UCB mononuclear cells through magnetic activation cell sorting (MACS) with purity of (≥ 90%) and were subjected to differentiate into NK cells. After 21 days of induction with SFTG36 (SCF, FLt-3L, TPO, GM-CSF, IL-3 and IL-6), IS721 (IGF-1, SIS3, IL-7 and IL-21) and IL-15/Hsp70 media, NK cells phenotypes were studied and their cytotoxicity against K562 human erythroleukemia cells and SKOV3 ovarian carcinoma cells was analyzed.

Results

The NK cells induced in SFTG36/IS721 medium were selected for activation due to their higher expression of CD56 + 16 + CD3 −  (93.23% ± 0.75) and mean fluorescence intensity (MFI) of NKG2D + (168.66 ± 20.00) and also a higher fold expansion potential (11.893 ± 1.712) compared to the other groups. These cells once activated with IL-15, demonstrated a higher cytotoxicity against K562 (≥ 90%; P ≤ 0.001) and SKOV3 tumor cells (≥ 65%; P ≤ 0.001) compared to IL-15/Hsp70-activated NK cells.

Conclusions

The differentiation of ex vivo expanded CD34 + cells through manipulation of RAS/MAPK, IGF-1R and TGF-β signaling pathways is an efficient approach for generating functional NK cells that can be used for cancer immunotherapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-01983-z.

Transcription Factors Associated With IL-15 Cytokine Signaling During NK Cell Development

Natural killer (NK) cells are lymphocytes primarily involved in innate immunity and possess important functional properties in anti-viral and anti-tumor responses; thus, these cells have broad potential for clinical utilization. NK cells originate from hematopoietic stem cells (HSCs) through the following two independent and continuous processes: early commitment from HSCs to IL-15-responsive NK cell progenitors (NKPs) and subsequent differentiation into mature NK cells in response to IL-15. IL-15 is the most important cytokine for NK cell development, is produced by both hematopoietic and nonhematopoietic cells, and functions through a distinct delivery process termed transpresentation. Upon being transpresented to NK cells, IL-15 contributes to NK cell development via the activation of several downstream signaling pathways, including the Ras-MEK-MAPK, JAK-STAT5, and PI3K-ATK-mTOR pathways. Nonetheless, the exact role of IL-15 in NK cell development has not been discussed in a consecutive and comprehensive manner. Here, we review current knowledge about the indispensable role of IL-15 in NK cell development and address which cells produce IL-15 to support NK cell development and when IL-15 exerts its function during multiple developmental stages. Specifically, we highlight how IL-15 supports NK cell development by elucidating the distinct transpresentation of IL-15 to NK cells and revealing the downstream target of IL-15 signaling during NK cell development.

Multiparameter Flow Cytometry Analysis of the Human Spleen Applied to Studies of Plasma-Derived EVs From Plasmodium vivax Patients

The spleen is a secondary lymphoid organ with multiple functions including the removal of senescent red blood cells and the coordination of immune responses against blood-borne pathogens, such as malaria parasites. Despite the major role of the spleen, the study of its function in humans is limited by ethical implications to access human tissues. Here, we employed multiparameter flow cytometry combined with cell purification techniques to determine human spleen cell populations from transplantation donors. Spleen immuno-phenotyping showed that CD45⁺ cells included B (30%), CD4⁺ T (16%), CD8⁺ T (10%), NK (6%) and NKT (2%) lymphocytes. Myeloid cells comprised neutrophils (16%), monocytes (2%) and DCs (0.3%). Erythrocytes represented 70%, reticulocytes 0.7% and hematopoietic stem cells 0.02%. Extracellular vesicles (EVs) are membrane-bound nanoparticles involved in intercellular communication and secreted by almost all cell types. EVs play several roles in malaria that range from modulation of immune responses to vascular alterations. To investigate interactions of plasma-derived EVs from Plasmodium vivax infected patients (PvEVs) with human spleen cells, we used size-exclusion chromatography (SEC) to separate EVs from the bulk of soluble plasma proteins and stained isolated EVs with fluorescent lipophilic dyes. The integrated cellular analysis of the human spleen and the methodology employed here allowed in vitro interaction studies of human spleen cells and EVs that showed an increased proportion of T cells (CD4+ 3 fold and CD8+ 4 fold), monocytes (1.51 fold), B cells (2.3 fold) and erythrocytes (3 fold) interacting with PvEVs as compared to plasma-derived EVs from healthy volunteers (hEVs). Future functional studies of these interactions can contribute to unveil pathophysiological processes involving the spleen in vivax malaria.

Generation of cell-derived matrices that support human NK cell migration and differentiation

Human NK cells are effectors of the innate immune system that originate from hematopoietic precursors in the bone marrow. While stromal cell lines that support NK cell development from hematopoietic precursors are often used to generate mature NK cells from lymphoid precursors in vitro, the nature of contributing factors of these stromal cells to the generation of functionally mature NK cells has been poorly described. Previous studies have shown that developing NK cells adhere to, and migrate on, developmentally supportive stroma. Here, we describe the generation of cell-derived matrices (CDMs) from a commonly used murine fetal liver stromal cell line. These CDMs are derived directly from the same EL08.1D2 stromal cell line known to support NK cell differentiation and contain ECM structural components fibronectin and collagen. We demonstrate that CDMs support NK cell adhesion and migration with similar properties as intact cells. Further, we show that CDMs support NK cell maturation from lymphoid precursors in vitro, albeit with reduced cell survival compared to intact cell-based differentiation. Together, these results describe a cell-free system that supports NK cell development and that can serve as a useful model for studying the nature of the biochemical interactions between NK cell developmental intermediates and developmentally supportive substrates.

From stem cell to immune effector: how adhesion, migration, and polarity shape T-cell and natural killer cell lymphocyte development in vitro and in vivo

Lymphocyte development is a complex and coordinated pathway originating from pluripotent stem cells during embryogenesis and continuing even as matured lymphocytes are primed and educated in adult tissue. Hematopoietic stem cells develop in a specialized niche that includes extracellular matrix and supporting stromal and endothelial cells that both maintain stem cell pluripotency and enable the generation of differentiated cells. Cues for lymphocyte development include changes in integrin-dependent cell motility and adhesion which ultimately help to determine cell fate. The capacity of lymphocytes to adhere and migrate is important for modulating these developmental signals both by regulating the cues that the cell receives from the local microenvironment as well as facilitating the localization of precursors to tissue niches throughout the body. Here we consider how changing migratory and adhesive phenotypes contribute to human natural killer (NK)- and T-cell development as they undergo development from precursors to mature, circulating cells and how our understanding of this process is informed by in vitro models of T- and NK cell generation.

A novel spleen-resident immature NK cell subset and its maturation in a T-bet-dependent manner

NK cells are thought to develop primarily in the bone marrow during adult life. However, increasing evidence shows that NK cell developmental intermediates can be found in different peripheral tissues with unique characteristics. Here, we identified a unique NK cell subset with the CD49a^-CD49b^- phenotype in the spleen. These cells displayed an immature phenotype and weak abilities in cytotoxicity and cytokine production. Adoptive transfer experiments revealed that they could develop into mature conventional NK (cNK) cells. Transcriptome analysis further confirmed their immature features. Parabiosis experiments revealed that these cells maintained tissue-resident properties in the spleen. Moreover, T-bet deficiency intrinsically impaired the ability of these cells to develop into mature cNK cells. Thus, our study identified a spleen-resident immature NK cell subset that could undergo extramedullary maturation in a T-bet dependent manner.

The characteristics of vessel lining cells in normal spleens and their role in the pathobiology of myelofibrosis

The CD34^-CD8α⁺, sinusoid lining, littoral cells (LCs), and CD34⁺CD8α^-, splenic vascular endothelial cells (SVECs) represent 2 distinct cellular types that line the vessels within normal spleens and those of patients with myelofibrosis (MF). To further understand the respective roles of LCs and SVECs, each was purified from normal and MF spleens, cultured, and characterized. Gene expression profiling indicated that LCs were a specialized type of SVEC. LCs possessed a distinct gene expression profile associated with cytoskeleton regulation, cellular interactions, endocytosis, and iron transport. LCs also were characterized by strong phagocytic activity, less robust tube-forming capacity and a limited proliferative potential. These characteristics underlie the role of LCs as cellular filters and scavengers. Although normal LCs and SVECs produced overlapping as well as distinct hematopoietic factors and adhesion molecules, the gene expression profile of MF LCs and SVECs distinguished them from their normal counterparts. MF SVECs were characterized by activated interferon signaling and cell cycle progression pathways and increased vascular endothelial growth factor receptor, angiopoietin-2, stem cell factor, interleukin (IL)-33, Notch ligands, and IL-15 transcripts. In contrast, the transcription profile of MF LCs was associated with mitochondrial dysfunction, reduced energy production, protein biosynthesis, and catabolism. Normal SVECs formed in vitro confluent cell layers that supported MF hematopoietic colony formation to a greater extent than normal colony formation. These data provide an explanation for the reduced density of LCs observed within MF spleens and indicate the role of SVECs in the development of extramedullary hematopoiesis in MF.

Mesenchymal stem cells in myeloproliferative disorders - focus on primary myelofibrosis

Primary myelofibrosis (PMF) is the most aggressive Philadelphia-negative (Ph-) myeloproliferative neoplasm (MPN), characterized by bone marrow (BM) insufficiency, myelofibrosis (MF), osteosclerosis, neoangiogenesis, and extramedullary hematopoiesis (EMH) in spleen and liver. Presently, there is no curative treatment for this disease and therapy consists primarily of symptom relief and, in selected cases, allogeneic hematopoietic stem cell transplant (alloHSCT). PMF's major defining characteristics, as well as several recently described aspects of its cellular and molecular pathophysiology all support a critical role for dysregulated cell-cell/cell-extracellular matrix interactions and cytokine/chemokine signaling within the BM niche in the natural history of this disease. This review will highlight current data concerning the involvement of the BM niche, particularly of mesenchymal stem cells (MSC), in PMF, and will then discuss the rationale for a stroma-directed treatment, and the advantages such an approach would offer over the current treatments focused on targeting the malignant clone.

CD56bright NK cells exhibit potent antitumor responses following IL-15 priming

NK cells, lymphocytes of the innate immune system, are important for defense against infectious pathogens and cancer. Classically, the CD56dim NK cell subset is thought to mediate antitumor responses, whereas the CD56bright subset is involved in immunomodulation. Here, we challenge this paradigm by demonstrating that brief priming with IL-15 markedly enhanced the antitumor response of CD56bright NK cells. Priming improved multiple CD56bright cell functions: degranulation, cytotoxicity, and cytokine production. Primed CD56bright cells from leukemia patients demonstrated enhanced responses to autologous blasts in vitro, and primed CD56bright cells controlled leukemia cells in vivo in a murine xenograft model. Primed CD56bright cells from multiple myeloma (MM) patients displayed superior responses to autologous myeloma targets, and furthermore, CD56bright NK cells from MM patients primed with the IL-15 receptor agonist ALT-803 in vivo displayed enhanced ex vivo functional responses to MM targets. Effector mechanisms contributing to IL-15-based priming included improved cytotoxic protein expression, target cell conjugation, and LFA-1-, CD2-, and NKG2D-dependent activation of NK cells. Finally, IL-15 robustly stimulated the PI3K/Akt/mTOR and MEK/ERK pathways in CD56bright compared with CD56dim NK cells, and blockade of these pathways attenuated antitumor responses. These findings identify CD56bright NK cells as potent antitumor effectors that warrant further investigation as a cancer immunotherapy.

Characterization of human fibroblastic reticular cells as potential immunotherapeutic tools

Fibroblastic reticular cells (FRCs) are essential players during adaptive immune responses not only as a structural support for the encounter of antigen-presenting cells and naive T lymphocytes but also as a source of modulatory signals. However, little is known about this cell population in humans. To address the phenotypical and functional analysis of human FRCs here we established splenic (SP) and mesenteric lymph node (LN) CD45^-CD31^-CD90⁺podoplanin⁺ myofibroblastic cell cultures. They shared the phenotypical characteristics distinctive of FRCs, including the expression of immunomodulatory factors and peripheral tissue antigens. Nevertheless, human FRCs also showed particular features, some differing from mouse FRCs, like the lack of nitric oxide synthase (NOS2) expression after interferon (IFN)γstimulation. Interestingly, SP-FRCs expressed higher levels of interleukin (IL)-6, BMP4, CCL2, CXCL12 and Notch molecules, and strongly adapted their functional profile to lipopolysaccharide (LPS), polyinosinic:polycytidylic acid (Poly I:C) and IFNγ stimulation. In contrast, we found higher expression of transforming growth factor (TGF)β and Activin A in LN-FRCs that barely responded via Toll-Like Receptor (TLR)3 and constitutively expressed retinaldehyde dehydrogenase 1 enzyme, absent in SP-FRCs. This study reveals human FRCs can be valuable models to increase our knowledge about the physiology of human secondary lymphoid organs in health and disease and to explore the therapeutic options of FRCs.

Axl signaling induces development of natural killer cells in vitro and in vivo

Natural killer (NK) cells have been well known to play a critical role in innate immunity, but they are also capable of regulating adaptive immunity through the induction of T cell-mediated memory response and B cell-mediated autoimmune response. NK cells are differentiated from hematopoietic stem cells (HSCs) in the bone marrow (BM), and a series of surface molecules are expressed on NK cells in a differentiation stage-specific manner. Axl receptor tyrosine kinase is originally identified as homeostatic regulators for antigen-presenting cells, and its ligand, growth-arrest-specific gene 6 (Gas6), has been reported to promote cell survival, proliferation, and migration, but their regulatory role in the development and effector function of NK cells is not yet fully understood. In this study, to investigate whether Axl is required for the regulation of NK cell development, the expression of mature NK (mNK) cell-specific receptors and NK cell-associated genes was analyzed in the differentiated HSCs-derived NK cells in vitro and the NK cells harvested from Axl^-/- mice. We found that agonistic anti-Axl antibody or recombinant Gas6 specifically upregulated the expression of mNK cell-specific receptors, such as LY49A, Ly49G2, Ly49C/F/I, NKG2A/C/E (1.5- to 3.5-fold increase), and NK cell-associated genes, such as IL-2Rβ (2.3- or 2.4-fold increase), Perforin (4.1- or 2.1-fold increase), IL-15Rα (2.14- or 2.04-fold increase), and IFN-γ (3.3- or 2.8-fold increase) compared to each isotype control, whereas it was abrogated by treatment of Axl-Ig. Anti-Axl antibody or rGas6 also induced a 2.5- or 1.9-fold increase in the proliferation of developing NK cells compared to each control, respectively. mNK cell populations expressing mNK cell-specific receptors were reduced about twofold in NK cells differentiated from HSCs of Axl^-/- mice compared with those of wild-type mice. Furthermore, the triggering of Axl signaling by agonistic anti-Axl antibody promoted the cytolytic activity (1.5- to 1.9-fold increase) against target tumor cells. In B16F10 melanoma-bearing mice, the number of metastatic colonies was decreased by 83 % by the administration of mNK cells treated with anti-Axl antibody compared to control Ig. These data suggest that Axl plays an essential role in the regulation of NK cell development as well as NK effector function.

TLR-9 and IL-15 Synergy Promotes the In Vitro Clonal Expansion of Chronic Lymphocytic Leukemia B Cells

Clinical progression of B cell chronic lymphocytic leukemia (B-CLL) reflects the clone's Ag receptor (BCR) and involves stroma-dependent B-CLL growth within lymphoid tissue. Uniformly elevated expression of TLR-9, occasional MYD88 mutations, and BCR specificity for DNA or Ags physically linked to DNA together suggest that TLR-9 signaling is important in driving B-CLL growth in patients. Nevertheless, reports of apoptosis after B-CLL exposure to CpG oligodeoxynucleotide (ODN) raised questions about a central role for TLR-9. Because normal memory B cells proliferate vigorously to ODN+IL-15, a cytokine found in stromal cells of bone marrow, lymph nodes, and spleen, we examined whether this was true for B-CLL cells. Through a CFSE-based assay for quantitatively monitoring in vitro clonal proliferation/survival, we show that IL-15 precludes TLR-9-induced apoptosis and permits significant B-CLL clonal expansion regardless of the clone's BCR mutation status. A robust response to ODN+IL-15 was positively linked to presence of chromosomal anomalies (trisomy-12 or ataxia telangiectasia mutated anomaly + del13q14) and negatively linked to a very high proportion of CD38(+) cells within the blood-derived B-CLL population. Furthermore, a clone's intrinsic potential for in vitro growth correlated directly with doubling time in blood, in the case of B-CLL with Ig H chain V region-unmutated BCR and <30% CD38(+) cells in blood. Finally, in vitro high-proliferator status was statistically linked to diminished patient survival. These findings, together with immunohistochemical evidence of apoptotic cells and IL-15-producing cells proximal to B-CLL pseudofollicles in patient spleens, suggest that collaborative ODN and IL-15 signaling may promote in vivo B-CLL growth.

Location and cellular stages of natural killer cell development

The identification of distinct tissue-specific natural killer (NK) cell populations that apparently mature from local precursor populations has brought new insight into the diversity and developmental regulation of this important lymphoid subset. NK cells provide a necessary link between the early (innate) and late (adaptive) immune responses to infection. Gaining a better understanding of the processes that govern NK cell development should allow us to harness better NK cell functions in multiple clinical settings, as well as to gain further insight into how these cells undergo malignant transformation. In this review, we summarize recent advances in understanding sites and cellular stages of NK cell development in humans and mice.

IL-15 expression on RA synovial fibroblasts promotes B cell survival

Introduction

The purpose of this study was to examine the role of RA Synovial Fibroblast (RASFib) IL-15 expression on B cell survival.

Methods

Magnetically sorted peripheral blood memory B cells from 15 healthy subjects were cocultured with RASFib.

Results

RASFib constitutively expressed membrane IL-15. Survival of isolated B cells cultured for 6 days, below 5%, was extended in coculture with RASFib to 52+/−8% (p<0.001). IL-15 neutralizing agents but not isotype controls, reduced this rate to 31+/−6% (p<0.05). Interestingly, rhIL-15 had no effect on isolated B cells but significantly increased their survival in coculture with RASFib. In parallel, B cell IL-15R chains were upregulated in cocultures. BAFF and VCAM-1, that are expressed on RASFib, were tested as potential candidates involved in upregulating B cell IL-15R. Culture of B cells in the presence of rhBAFF or rhVCAM-1 resulted in significantly increased survival, together with upregulation of all three IL-15R chains; in parallel, rhIL-15 potentiated the anti-apoptotic effect of BAFF and VCAM-1. Both BAFF and VCAM-1 neutralizing agents downmodulated the effect of RASFib on B cell survival and IL-15R expression. In parallel, rhIL-15 had a lower effect on the survival of B cells cocultured with RASFib in the presence of BAFF or VCAM-1 neutralizing agents. Peripheral blood B cells from 15 early RA patients demonstrated an upregulated IL-15R and increased survival in cocultures.

Conclusion

IL-15 expression on RASFib significantly contributes to the anti-apoptotic effect of RASFib on B cells. IL-15 action is facilitated by BAFF and VCAM-1 expressed on RASFib, through an upregulation of IL-15R chains.

Generation of CD2(+)CD8(+) NK Cells from c-kit(+) Bone Marrow Cells in Porcine

Natural killer (NK) cells provide one of the initial barriers of cellular host defense against pathogens, in particular intracellular pathogens. Because bone marrow-derived hematopoietic stem cells (HSCs), lymphoid protenitors, can give rise to NK cells, NK ontogeny has been considered to be exclusively lymphoid. Here, we show that porcine c-kit⁺ bone marrow cells (c-kit⁺ BM cells) develop into NK cells in vitro in the presence of various cytokines [interleukin (IL)-2, IL-7, IL-15, IL-21, stem cell factor (SCF), and fms-like tyrosine kinase-3 ligand (FLT3L)]. Adding hydrocortisone (HDC) and stromal cells greatly increases the frequency of c-kit⁺ BM cells that give rise to CD2⁺CD8⁺ NK cells. Also, intracellular levels of perforin, granzyme B, and NKG2D were determined by RT-PCR and western blotting analysis. It was found that of perforin, granzyme B, and NKG2D levels significantly were increased in cytokine-stimulated c-kit⁺ BM cells than those of controls. And, we compared the ability of the cytotoxicity of CD2⁺CD8⁺ NK cells differentiated by cytokines from c-kit⁺ BM cells against K562 target cells for 28 days. Cytokines-induced NK cells as effector cells were incubated with K562 cells as target in a ratio of 100:1 for 4 h once a week. In results, CD2⁺CD8⁺ NK cells induced by cytokines and stromal cells showed a significantly increased cytotoxicity 21 days later. Whereas, our results indicated that c-kit⁺ BM cells not pretreated with cytokines have lower levels of cytotoxicity. Taken together, this study suggests that cytokines-induced NK cells from porcine c-kit⁺ BM cells may be used as adoptive transfer therapy if the known obstacles to xenografting (e.g. immune and non-immune problems) were overcome in the future.

Cytotoxic functions and susceptibility to apoptosis of human CD56(bright) NK cells differentiated in vitro from CD34⁺ hematopoietic progenitors

Cytotoxic functions and susceptibility to apoptosis are crucial aspects of NK cells suitable to counter cancer after infusion in oncologic patients. To test the feasibility and the usefulness of infusing in vitro generated NK cells, these two features were investigated in NK cells developed in vitro from CD34⁺ hematopoietic progenitors. Purified CD34⁺ cells were cultured for 15-30 days with FLT-3 ligand (FLT3-L) and IL-15 with or without IL-21. To induce terminal differentiation, NK cells were cultured for further 15 days with IL-15, IL-21, or their combination. A CD56(dim) /CD16⁺ NK subset, expressing high level of perforin, granzymes, and LFA-1, appeared early in cultures with FLT3-L, IL-15, and IL-21, but it quickly died, indicating its predisposition to apoptosis. On the contrary, CD56(bright) NK cells generated after 30 days of culture with FLT3-L plus IL-15 did not show a considerable apoptosis, nevertheless only a subset of these cells expressed granzyme-B, perforin, LFA-1, and CD94-CD159a heterodimer, indicating a functional immaturity. Interestingly, further 15 days of culture with IL-21 plus IL-15 did not induce the generation of CD56(dim) cells from the CD56(bright) subset and actually inhibited IL-15-induced maturation/activation of this latter subset. In fact, IL-15 alone upregulated granzyme-B, TRAIL, Fas ligand, CD94-CD159a, LFA-1, CD16, KIRs, and TRAIL-R2 on CD56(bright) NK cells. Our results suggest that during differentiation CD56(bright) NK cells, similarly to mature activated NK cells, become highly cytotoxic and are relatively resistant to apoptosis induced by TNF family members.

Ex vivo differentiation of natural killer cells from human umbilical cord blood CD34+ progenitor cells

Natural Killer (NK)-cells are peripheral blood lymphocytes that represent an important arm of the innate immune system. NK-cells play a critical role in the immune surveillance against tumors and virally infected cells in a major histocompatibiliy complex (MHC)-unrestricted fashion. We have explored such capacities of NK-cells after differentiation from hematopoietic stem and progenitor cells derived from human umbilical cord blood. Several culture conditions have been established supporting proliferation and subsequent differentiation of these cells in terms of receptor expression and specific lysis depending on the growth conditions in the presence and absence of supportive stromal feeders. We show that acquisition of Killer Immunoglobulin Receptor (KIR) as well as NK Cytotoxicity Receptor expressions is independent of culture condition whereas absence of stromal feeders did not support acquisition of CD94/NKG2A expression. Such KIR-positive/NKG2A-negative cells generated under different culture conditions showed strong and specific cytolytic activity which could have impact on further immunotherapeutic strategies.

Monocytes and T cells cooperate to favor normal and follicular lymphoma B-cell growth: role of IL-15 and CD40L signaling

Interleukin-15 (IL-15) has been extensively studied for its role in the survival and proliferation of NK and T cells through a unique mechanism of trans-presentation by producer cells. Conversely, whereas activated B cells have been described as IL-15-responding cells, the cellular and molecular context sustaining this effect remains unexplored. In this study, we found that, whereas human B cells could not respond to soluble IL-15, monocytes and lymphoid tissue-derived macrophages but not stromal cells efficiently trans-present IL-15 to normal B cells and cooperate with T-cell-derived CD40L to promote IL-15-dependent B-cell proliferation. Furthermore, CD40L signaling triggers a Src-independent upregulation of STAT5 expression and favors a Src-dependent phosphorylation of STAT5 in response to IL-15. In follicular lymphoma (FL), immunohistochemical studies reported a strong relationship between malignant B cells, infiltrating macrophages and T cells. We show here an overexpression of IL-15 in purified tumor-associated macrophages, and STAT5A in purified tumor B cells. Moreover, FL B cells respond to IL-15 trans-presented by monocytes/macrophages, in particular, in the presence of CD40L-mediated signaling. This cooperation between IL-15 and CD40L reinforces the importance of tumor microenvironment and unravels a mechanism of FL growth that should be considered if using IL-15 as a drug in this disease.

Plasticity of NK-cell differentiation

In this issue of Blood, Grzywacz and colleagues provide in vitro experimental evidence that human natural killer (NK) lymphocytes may derive from myeloid precursors and that microenvironmental factors such as stromal cells and hydrocortisone (HDC) may play a key role in favoring such differentiation.

Monocytes enhance cell proliferation and LMP1 expression of nasal natural killer/T-cell lymphoma cells by cell contact-dependent interaction through membrane-bound IL-15

Nasal natural killer (NK)/T-cell lymphoma (NNKTL) is an Epstein-Barr virus (EBV)-related malignancy with poor prognosis and has distinct histological features characterized by angiocentric and polymorphous lymphoreticular infiltrates including inflammatory cells such as granulocytes, monocytes, macrophages and lymphocytes. Here, we show that the monocytes enhance proliferation as well as LMP1 expression of NNKTL cells by cell contact-dependent interaction through membrane-bound interleukin (IL)-15. We used two EBV-positive NK-cell lines, SNK6 and KAI3, which originated from two patients-SNK6 from a patient with NNKTL and KAI3 from a patient with a severe mosquito allergy. We cocultured the cell lines with granulocytes or monocytes and examined whether proliferation, survival and LMP1 expression of the cells changed. Although cocultured granulocytes did not affect proliferation, survival or LMP1 expression of the cells, cocultured monocytes enhanced both proliferation and LMP1 expression in a dose-dependent manner. These phenomena were not seen when monocytes were placed in a separate chamber. Moreover, the monocyte-inducible proliferation and LMP1 expression were inhibited by treatment with an antibody against IL-15. Furthermore, production of interferon-gamma-inducible protein (IP)-10 were enhanced by coculture with monocytes and were inhibited by the antibody. Immunohistological studies confirmed that a number of infiltrating CD14-positive monocytes contacted CD56-positive lymphoma cells in all of 20 NNKTL tissues tested. These results suggest that monocytes enhance cell growth as well as LMP1 expression of NNKTL cells by cell contact-dependent interaction through membrane-bound IL-15. In the microenvironment of NNKTL tissue, a positive feedback loop of interaction between lymphoma cells and monocytes may be present and contribute to lymphoma progression.

CD34+ hematopoietic precursors are present in human decidua and differentiate into natural killer cells upon interaction with stromal cells

Natural killer (NK) cells are the main lymphoid population in the maternal decidua during the first trimester of pregnancy. Decidual NK (dNK) cells display a unique functional profile and play a key role in promoting tissue remodeling, neoangiogenesis, and immune modulation. However, little information exists on their origin and development. Here we discovered CD34(+) hematopoietic precursors in human decidua (dCD34(+)). We show that dCD34(+) cells differ from cord blood- or peripheral blood-derived CD34(+) precursors. The expression of IL-15/IL-2 receptor common β-chain (CD122), IL-7 receptor α-chain (CD127), and mRNA for E4BP4 and ID2 transcription factors suggested that dCD34(+) cells are committed to the NK cell lineage. Moreover, they could undergo in vitro differentiation into functional (i.e., IL-8- and IL-22-producing) CD56(bright)CD16(-)KIR(+/-) NK cells in the presence of growth factors or even upon coculture with decidual stromal cells. Their NK cell commitment was further supported by the failure to undergo myeloid differentiation in the presence of GM-CSF. Our findings strongly suggest that decidual NK cells may directly derive from CD34(+) cell precursors present in the decidua upon specific cellular interactions with components of the decidual microenvironment.

Natural killer-cell differentiation by myeloid progenitors

Because lymphoid progenitors can give rise to natural killer (NK) cells, NK ontogeny has been considered to be exclusively lymphoid. Here, we show that rare human CD34(+) hematopoietic progenitors develop into NK cells in vitro in the presence of cytokines (interleukin-7, interleukin-15, stem cell factor, and fms-like tyrosine kinase-3 ligand). Adding hydrocortisone and stromal cells greatly increases the frequency of progenitor cells that give rise to NK cells through the recruitment of myeloid precursors, including common myeloid progenitors and granulocytic-monocytic precursors to the NK-cell lineage. WNT signaling was involved in this effect. Cells at more advanced stages of myeloid differentiation (with increasing expression of CD13 and macrophage colony-stimulating factor receptor [M-CSFR]) could also differentiate into NK cells in the presence of cytokines, stroma, and hydrocortisone. NK cells derived from myeloid precursors (CD56(-)CD117(+)M-CSFR(+)) showed more expression of killer immunoglobulin-like receptors, a fraction of killer immunoglobulin-like receptor-positive-expressing cells that lacked NKG2A, a higher cytotoxicity compared with CD56(-)CD117(+)M-CSFR(-) precursor-derived NK cells and thus resemble the CD56(dim) subset of NK cells. Collectively, these studies show that NK cells can be derived from the myeloid lineage.

Interleukin-15 enhances proliferation and chemokine secretion of human follicular dendritic cells

The germinal centre (GC) is a specialized microenvironment where high-affinity antibodies are produced through hypermutation and isotype switching. Follicular dendritic cells (FDCs) are the stromal cells of the GC. The timely expansion and establishment of an FDC network is essential for a protective GC reaction; however, only a few factors modulating FDC development have been recognized. In this study, we report that interleukin-15 (IL-15) enhances human primary FDC proliferation and regulates cytokine secretion. The FDCs express IL-15 receptor complexes for IL-15 signal transduction as well as for specific binding. Moreover, the secretion of chemokines CCL-2, CCL-5, CXCL-5 and CXCL-8 was reduced by blocking IL-15 signalling while the secretion of other cytokines, and the expression of CD14, CD44, CD54 (ICAM-1) and CD106 (VCAM-1) proteins remained unchanged. These results suggest that IL-15 plays a crucial role in the development of FDC networks during GC reaction, offering a new target for immune modulation.

A dual action of rheumatoid arthritis synovial fibroblast IL-15 expression on the equilibrium between CD4+CD25+ regulatory T cells and CD4+CD25- responder T cells

We previously described that fibroblast-like cells from the synovium of rheumatoid arthritis patients (RASFib) constitutively express intracellular and surface IL-15, which induces activation of cocultured T cells. Our objective was to study the effect of RASFib IL-15 expression on the function of human CD4(+)CD25(+) regulatory T cells (Treg). RASFib, through their constitutive IL-15 expression, were able to induce the proliferation of human Tregs stimulated through their TCR, and at the same time potentiated their suppressive action on the cytokine secretion of CD4(+)CD25(-) responder T cells (Tresp). In parallel, constitutive RASFib IL-15 expression mediated an up-regulated response of Tresp. Subsequently, total CD4(+) T cells, containing natural proportions of Treg and Tresp, secreted an increased amount of pathogenic cytokines when cocultured with RASFib despite the presence of proliferating Treg with superior regulatory potency. In summary, RASFib IL-15 exerts a dual action on the equilibrium between Treg and Tresp by potentiating the suppressive effect of Treg while augmenting the proinflammatory action of Tresp; the result is a shift of the Treg/Tresp balance toward a proinflammatory state. This alteration of the Treg/Tresp equilibrium is not observed in the presence of osteoarthritis synovial fibroblasts or dermal fibroblasts, which do not constitutively express surface IL-15. Additionally, Treg with superior suppressive potency were present in the peripheral blood and the synovial fluid of RA patients, but this enhanced immunoregulatory activity was not able to overcome the increased secretion of pathogenic cytokines by RA-Tresp, indicating that rheumatoid arthritis patients demonstrate an altered Treg/Tresp equilibrium in vivo.

Hepatocytes and IL-15: a favorable microenvironment for T cell survival and CD8+ T cell differentiation

Human intrahepatic lymphocytes are enriched in CD1d-unrestricted T cells coexpressing NKR. Although the origin of this population remains controversial, it is possible to speculate that the hepatic microenvironment, namely epithelial cells or the cytokine milieu, may play a role in its shaping. IL-15 is constitutively expressed in the liver and has a key role in activation and survival of innate and tissue-associated immune cells. In this in vitro study, we examined whether hepatocyte cell lines and/or IL-15 could play a role in the generation of NK-like T cells. The results show that both HepG2 cells and a human immortalized hepatocyte cell line increase survival and drive basal proliferation of T cells. In addition, IL-15 was capable of inducing Ag-independent up-regulation of NKR, including NKG2A, Ig-like receptors, and de novo expression of CD56 and NKp46 in CD8(+)CD56(-) T cells. In conclusion, our study suggests that hepatocytes and IL-15 create a favorable microenvironment for T cells to growth and survive. It can be proposed that the increased percentage of intrahepatic nonclassical NKT cells could be in part due to a local CD8(+) T cell differentiation.

Does primary myelofibrosis involve a defective stem cell niche? From concept to evidence

Primary myelofibrosis (PMF) is the rarest and the most severe Philadelphia-negative chronic myeloproliferative syndrome. By associating a clonal proliferation and a mobilization of hematopoietic stem cells from bone marrow to spleen with profound alterations of the stroma, PMF is a remarkable model in which deregulation of the stem cell niche is of utmost importance for the disease development. This paper reviews key data suggesting that an imbalance between endosteal and vascular niches participates in the development of clonal stem cell proliferation. Mechanisms by which bone marrow niches are altered with ensuing mobilization and homing of neoplastic hematopoietic stem cells in new or reinitialized niches in the spleen and liver are examined. Differences between signals delivered by both endosteal and vascular niches in the bone marrow and spleen of patients as well as the responsiveness of PMF stem cells to their specific signals are discussed. A proposal for integrating a potential role for the JAK2 mutation in their altered sensitivity is made. A better understanding of the cross talk between stem cells and their niche should imply new therapeutic strategies targeting not only intrinsic defects in stem cell signaling but also regulatory hematopoietic niche-derived signals and, consequently, stem cell proliferation.

Generation of a novel regulatory NK cell subset from peripheral blood CD34+ progenitors promoted by membrane-bound IL-15

BACKGROUND

NK cells have been long time considered as cytotoxic lymphocytes competent in killing virus-infected cells and tumors. However, NK cells may also play essential immuno-regulatory functions. In this context, the real existence of a defined NK subset with negative regulatory properties has been hypothesized but never clearly demonstrated.

METHODOLOGY/PRINCIPAL FINDINGS

Herein, we show the in vitro generation from human peripheral blood haematopoietic progenitors (PB-HP), of a novel subset of non-cytolytic NK cells displaying a mature phenotype and remarkable immuno-regulatory functions (NK-ireg). The main functional hallmark of these NK-ireg cells is represented by the surface expression/release of HLA-G, a major immunosuppressive molecule. In addition, NK-ireg cells secrete two powerful immuno-regulatory factors: IL-10 and IL-21. Through these factors, NK-ireg cells act as effectors of the down-regulation of the immune response: reconverting mature myeloid DC (mDC) into immature/tolerogenic DC, blocking cytolytic functions on conventional NK cells and inducing HLA-G membrane expression on PB-derived monocytes. The generation of "NK-ireg" cells is obtained, by default, in culture conditions favouring cell-to-cell contacts, and it is strictly dependent on reciprocal trans-presentation of membrane-bound IL-15 forms constitutively and selectively expressed by human CD34(+) PB-HP. Finally, a small subset of NKp46(+) HLA-G(+) IL-10(+) is detected within freshly isolated decidual NK cells, suggesting that these cells could represent an in vivo counterpart of the NK-ireg cells.

CONCLUSIONS/SIGNIFICANCE

In conclusion, NK-ireg cells represent a novel truly differentiated non-cytolytic NK subset with a self-sustainable phenotype (CD56(+) CD16(+) NKp30(+) NKp44(+) NKp46(+) CD94(+) CD69(+) CCR7(+)) generated from specific pSTAT6(+) GATA3(+) precursors. NK-ireg cells could be employed to develop new immuno-suppressive strategies in autoimmune diseases, transplant rejection or graft versus host diseases. In addition, NK-ireg cells can be easily derived from peripheral blood of the patients and could constitute an autologous biotherapic tool to be used combined or in alternative to other immuno-regulatory cells.

Subcellular expression pattern and role of IL-15 in pneumococci induced lung epithelial apoptosis

Streptococcus pneumoniae is the leading causative agent of community-acquired pneumonia. Induction of apoptosis in pulmonary epithelial cells by bacteria during pneumonia might be harmful to the host. Interleukin-15 (IL-15) has been demonstrated as an effective inhibitor of apoptosis and is expressed in lung epithelium on the mRNA and protein level. Therefore, we characterized the sub-cellular expression pattern of the short and long IL-15 isoforms in lung epithelial cells in vitro as well as its role in pneumococci-related lung epithelial cell apoptosis. We found an expression pattern for both IL-15 signal peptides in the pulmonary epithelial cell lines A549 and Beas-2B. Moreover, a strong co-localization of IL-15 and IL-15Ralpha was detected on cell surfaces. Compared to pro-inflammatory cytokine stimulation, neither IL-15 nor its trimeric receptor complex was up-regulated after pneumococcal infection. However, overexpression of IL-15 isoforms revealed IL-15LSP and IL-15Vkl as inhibitors of pneumococci induced apoptosis in pulmonary epithelial cells. Thus, IL-15 may act as an anti-apoptotic molecule in pneumococci infection, thereby suggesting IL-15 as a benefical cytokine in pulmonary host defense against infection.

CD56bright human NK cells differentiate into CD56dim cells: role of contact with peripheral fibroblasts

Human NK cells are divided into CD56(bright)CD16(-) cells and CD56(dim)CD16(+) cells. We tested the hypothesis that CD56(bright) NK cells can differentiate into CD56(dim) cells by prospectively isolating and culturing each NK subset in vitro and in vivo. Our results show that CD56(bright) cells can differentiate into CD56(dim) both in vitro, in the presence of synovial fibroblasts, and in vivo, upon transfer into NOD-SCID mice. In vitro, this differentiation was inhibited by fibroblast growth factor receptor-1 Ab, demonstrating a role of the CD56 and fibroblast growth factor receptor-1 interaction in this process. Differentiated CD56(dim) cells had reduced IFN-gamma production but increased perforin expression and cytolysis of cell line K562 targets. Flow cytometric fluorescent in situ hybridization demonstrated that CD56(bright) NK cells had longer telomere length compared with CD56(dim) NK cells, implying the former are less mature. Our data support a linear differentiation model of human NK development in which immature CD56(bright) NK cells can differentiate into CD56(dim) cells.

Coordinated acquisition of inhibitory and activating receptors and functional properties by developing human natural killer cells

The stages of human natural killer (NK) cell differentiation are not well established. Culturing CD34(+) progenitors with interleukin 7 (IL-7), IL-15, stem cell factor (SCF), FLT-3L, and murine fetal liver cell line (EL08.1D2), we identified 2 nonoverlapping subsets of differentiating CD56(+) cells based on CD117 and CD94 (CD117(high)CD94(-) and CD117(low/-)CD94(+) cells). Both populations expressed CD161 and NKp44, but differed with respect to NKp30, NKp46, NKG2A, NKG2C, NKG2D, CD8, CD16, and KIR. Only the CD117(low/-) CD94(+) population displayed cytotoxicity and interferon-gamma production. Both populations arose from a single CD34(+)CD38(-) Lin(-) cell and their percentages changed over time in a reciprocal fashion, with CD117(high)CD94(-) cells predominating early and decreasing due to an increase of the CD117(low/-)CD94(+) population. These 2 subsets represent distinct stages of NKcell differentiation, since purified CD117(high) CD94(-) cells give rise to CD117(low/-)CD94(+) cells. The stromal cell line (EL08.1D2) facilitated the transition from CD117(high)CD94(-) to CD117(low/-)CD94(+) via an intermediate phenotype (CD117(low)CD94(low/-)). EL08.1D2 also maintained the mature phenotype, preventing the reversion of CD117(low/-)CD94(+) cells to the intermediate (CD117(low)CD94(low/-)) phenotype. An analogous population of CD56(+)CD117(high)CD94(-) cells was found in cord blood. The identified stages of NK-cell differentiation provide evidence for coordinated acquisition of HLA-specific inhibitory receptors (ie, CD94/NKG2A) and function in developing human NK cells.

The interleukin-15/interleukin-15 receptor system as a model for juxtacrine and reverse signaling

Interleukin-15 (IL-15) is a pleiotropic cytokine of the 4 alpha-helix bundle family, which binds to a receptor complex that displays common elements with the IL-2 receptor and a unique high-affinity alpha chain. This review focuses on juxtacrine and reverse signaling levels in the IL-15/IL-15R system. Specifically, we discuss how agonistic stimulation of membrane-bound IL-15 induces phosphorylation of members of the MAP kinase family and of focal adhesion kinase (FAK), thereby upregulating processes including cytokine secretion, cell adhesion and migration. In addition, we explore IL-15 trans-presentation and intracellular signaling, and define promising molecular targets for future pharmacological intervention in infectious diseases and immunological disorders. These frontiers in IL-15/IL-15Ralpha research serve as highly instructive examples for key concepts, unsolved problems and therapeutic opportunities in juxtacrine and reverse signaling in general.

Interleukin-12 is not essential for silicosis in mice

BACKGROUND

Silicosis features foci of inflammation where macrophages and lymphocytes precede and accompany fibroblast proliferation, alveolar epithelial hyperplasia, and increased deposition of connective tissue matrix material. In the mouse following silica inhalation there is recruitment of natural killer-, B-, and CD4+ and CD8+ lymphocytes to the alveolar spaces, enlargement of bronchial-associated lymphoid tissues (BALT), and aggregation of lymphocytes surrounding small airways and blood vessels. A substantial fraction of the recruited lung lymphocytes produce interferon-gamma (IFN-gamma), and IFN-gamma gene-deleted mice develop less silicosis than wild-type mice. Interleukin-12 (IL-12) is an important pathway for driving the adaptive immune response towards a TH1-like phenotype. We hypothesized that IL-12 might stimulate lymphocyte activation and the up-regulation of IFN-gamma, and consequently be an essential mediator for silicosis.

RESULTS

C57Bl/6 wild-type (WT) and IL-12 deficient (IL-12 KO) mice were exposed to sham-air or crystobalite silica (61 mg/m3) by inhalation for 5 hours/day for 12 days and then studied from 1 to 112 days after exposure. Mice exposed to sham-air had normal lung histology at all time points. WT mice exposed to titanium dioxide (72 mg/m3) showed pulmonary macrophage recruitment but no increase in lung collagen. Both WT and IL-12 KO mice exposed to silica showed similar progressive lung pathology, increased wet lung weight and increased total lung collagen (hydroxyproline). IL-12 p35 mRNA was not increased in either strain after silica exposure; IL-12 p40 mRNA was up-regulated after silica in WT mice and constitutively absent in the IL-12 KO mice. IL-18 mRNA was not increased after silica exposure. The expression of IL-15 (an important driver for innate immunity, Natural Killer cell activation, and IFN-gamma production) was abundant in air-exposed mice and was increased slightly in the lungs of mice with silicosis.

CONCLUSION

The axis of IL-12 driving IFN-gamma production is not essential for the full manifestations of silicosis in mice exposed to a crystobalite silica aerosol.

Peripheral blood T lymphocytes from patients with early rheumatoid arthritis express RANKL and interleukin-15 on the cell surface and promote osteoclastogenesis in autologous monocytes

OBJECTIVE

To investigate the osteoclastogenic potential of T cells from the peripheral blood (PB) and synovial fluid (SF) of patients with rheumatoid arthritis (RA) on autologous monocytes, and to study the cytokines implicated in this process.

METHODS

T cells and monocytes were isolated from the PB of 20 healthy subjects and 20 patients with early RA, and from the SF of 20 patients with established RA. Autologous T cell/monocyte cocultures were established in the absence of exogenous cytokines or growth factors in order to examine spontaneous ex vivo osteoclast differentiation by tartrate-resistant acid phosphatase staining and calcified matrix resorption activity.

RESULTS

Surface RANKL was expressed on freshly isolated T cells from the PB of patients with early RA and the SF of patients with established RA. In addition, surface interleukin-15 (IL-15) was detected on freshly isolated T cells and monocytes from the PB of patients with early RA and the SF of patients with established RA. Autologous T cell/monocyte cocultures derived from the SF of patients with established RA and from the PB of patients with early RA, but not from the PB of healthy controls, resulted in osteoclast differentiation that was significantly inhibited by osteoprotegerin (OPG) and by neutralizing monoclonal antibodies to IL-15, IL-17, tumor necrosis factor alpha (TNFalpha), and IL-1beta. OPG, anti-TNFalpha, and anti-IL-1beta demonstrated a cooperative inhibitory effect. At 1-year followup, surface RANKL and IL-15 and ex vivo osteoclastogenesis were no longer observed on PB T cells or monocytes from patients with early RA in whom clinical remission had been achieved with treatment.

CONCLUSION

T cells are important contributors to the pathogenesis of bone erosions in RA through interaction with osteoclast precursors of the monocyte/macrophage lineage.

Stage-dependent gene expression profiles during natural killer cell development

Natural killer (NK) cells develop from hematopoietic stem cells (HSCs) in the bone marrow. To understand the molecular regulation of NK cell development, serial analysis of gene expression (SAGE) was applied to HSCs, NK precursor (pNK) cells, and mature NK cells (mNK) cultured without or with OP9 stromal cells. From 170,464 total individual tags from four SAGE libraries, 35,385 unique genes were identified. A set of genes was expressed in a stage-specific manner: 15 genes in HSCs, 30 genes in pNK cells, and 27 genes in mNK cells. Among them, lipoprotein lipase induced NK cell maturation and cytotoxic activity. Identification of genome-wide profiles of gene expression in different stages of NK cell development affords us a fundamental basis for defining the molecular network during NK cell development.

Membrane-bound and soluble IL-15/IL-15Rα complexes display differential signaling and functions on human hematopoietic progenitors

Membrane-bound and soluble interleukin-15 (IL-15)/IL-15 receptor α (Rα) complexes trigger differential transcription factor activation and functions on human hematopoietic progenitors. Indeed, human spleen myofibroblasts (SMFs) are characterized by a novel mechanism of IL-15 trans-presentation (SMFmb [membrane-bound]-IL-15), based on the association of an endogenous IL-15/IL-15Rα complex with the IL-15Rβγc chains. SMFmb-IL-15 (1) induces lineage-specific signaling pathways that differ from those controlled by soluble IL-15 in unprimed and committed normal progenitors; (2) triggers survival and proliferation of leukemic progenitors expressing low-affinity IL-15R (M07Sb cells); (3) causes only an antiapoptotic effect on leukemic cells expressing high-affinity receptors (TF1β cells). This behavior is likely due to the IL-15Rα chain present on these cells that interact with the SMFmb-IL-15, inhibiting signal transducer and transcriptional activator 5 (STAT5) activation. On the other hand, the soluble IL-15/IL-15Rα complex (hyper IL-15) displays a dominant pattern of action, activating only those cells expressing low-affinity IL-15R (IL-15Rβγc). Thus, hyper IL-15 induces antiapoptotic effects on M075b cells and the up-regulation of STAT6 activation on adult peripheral blood (PB) pre-natural killer (NK) committed progenitors. The latter effect using 100-fold concentrations of recombinant (r)-IL-15. In conclusion, SMFmb-IL-15 and soluble IL-15Rα/IL-15 complexes seem to play a pivotal role in the control of the survival, proliferation and differentiation of both normal and leukemic circulating progenitors, highlighting new functions of IL-15 and of IL-15Rα.

Involvement of human natural killer cells in asthma pathogenesis: natural killer 2 cells in type 2 cytokine predominance

BACKGROUND

T H 2 cells play a pivotal role in the pathogenesis of human asthma. Natural killer (NK) cells are also thought to divide into NK1 and NK2 subsets.

OBJECTIVE

Whether NK1 or NK2 cells are involved in asthma remains unclear.

METHODS

Triple-color flow cytometry for detecting intracellular cytokine and NK cell surface phenotype from asthmatic patients was used. The NK cell cloning and analysis with RT-PCR for cytokine expression and Western blotting for signal transducer and activator of transcription activation were performed.

RESULTS

For the first time, we observed that the ratio of IL-4 + CD56 + NK2 cells in PBMCs of 8 asthmatic patients were higher than in healthy individuals. NK cell clones were then obtained by means of limited dilution, and the average mean of the relative intensity of PCR products for type 2 cytokines significantly increased in the asthmatic patients. Signal transducer and activator of transcription 6, a key transcript factor of type 2 phenotype, was constitutively activated in NK2 clones from asthmatic patients. We cocultured freshly purified NK cells from asthmatic patients with IFN-gamma and anti-IL-4 antibody in the presence of IL-15 and found that the content of IL-4 + NK2 cells significantly decreased after treatment. Interestingly, NK2-biased status in asthmatic patients was reversed when patients recovered from regular therapy.

CONCLUSION

The results suggest that the NK2 cell subset is involved in the pathogenesis of asthma.

Importance of stromal determinants in the generation of dendritic and natural killer cells in the human spleen

Summary The interaction between stroma and blood cells in the human spleen has received little attention, despite their well-defined roles during blood cell development in bone marrow. We have reported previously that human spleen-derived fibroblasts display a differentiated myofibroblast phenotype and constitutively express a biologically active form of membrane interleukin (IL)-15 that can drive co-cultured CD34(+) blood cells to differentiate into activated natural killer (NK) cells. Here, we show that, in addition to NK cells, CD34/fibroblast co-cultures also yield myeloid CD1a(+)CD38(+)CD68(+)CD86(+) HLA-DR(+)CD14(-)CD80(-) dendritic cells (DCs) after 3-4 weeks in culture. We found that DC development depended on endogenously secreted stromal macrophage colony-stimulating factor (M-CSF) and CD40/CD40L interaction rather than on fibroblast- and CD34-derived membrane IL-15. CD1a(+) cells were necessary for co-produced NK cells to acquire lytic functions by a mechanism involving cell-to-cell contact and DC-derived IL-12. This study highlights the importance of spleen myofibroblasts in the in vitro generation of two distinct cell types (DC and NK cells) from the innate immune system and suggests that the human spleen is involved in the generation of NK cells from circulating progenitors.

CD34+ cells cultured in stem cell factor and interleukin-2 generate CD56+ cells with antiproliferative effects on tumor cell lines

In vitro stimulation of CD34+ cells with IL-2 induces NK cell differentiation. In order to define the stages of NK cell development, which influence their generation from CD34 cells, we cultured G-CSF mobilized peripheral blood CD34+ cells in the presence of stem cell factor and IL-2. After three weeks culture we found a diversity of CD56+ subsets which possessed granzyme A, but lacked the cytotoxic apparatus required for classical NK-like cytotoxicity. However, these CD56+ cells had the unusual property of inhibiting proliferation of K562 and P815 cell lines in a cell-contact dependent fashion.

Follicular dendritic cells produce IL-15 that enhances germinal center B cell proliferation in membrane-bound form

Factors that control the survival and proliferation of Ag-stimulated B cells within the germinal center (GC) are crucial for humoral immune responses with high affinity Abs against infectious agents. The follicular dendritic cell (FDC) is known as a key cellular component of the GC microenvironment for GC-B cell survival and proliferation. In this study, we report that IL-15 is produced by human FDC in vivo and by an FDC cell line, FDC/HK cells, in vitro. IL-15 is captured by IL-15Ralpha on the surface of FDC/HK cells. The surface IL-15 is functionally active and augments GC-B cell proliferation. Because GC-B cells have the signal-transducing components (IL-2/15Rbetagamma), but not a receptor for binding of soluble IL-15 (IL-15Ralpha), IL-15 signaling is possibly transduced by transpresentation from FDCs to GC-B cells via cell-cell contact. Together, these results suggest that IL-15 from FDC, in membrane-bound form, plays an important role in supporting GC-B cell proliferation, proposing a new target for immune modulation as well as treatment of B cell tumors of GC origin.

Interleukin-2, Interleukin-15, and Their Roles in Human Natural Killer Cells

Natural killer (NK) cells are CD56+CD3- large granular lymphocytes that constitute a key component of the human innate immune response. In addition to their potent cytolytic activity, NK cells elaborate a host of immunoregulatory cytokines and chemokines that play a crucial role in pathogen clearance. Furthermore, interactions between NK and other immune cells are implicated in triggering the adaptive, or antigen-specific, immune response. Interleukin-2 (IL-2) and IL-15 are two distinct cytokines with partially overlapping properties that are implicated in the development, homeostasis, and function of NK cells. This review examines the pervasive effects of IL-2 and IL-15 on NK cell biology, with an emphasis on recent discoveries and lingering challenges in the field.

Hepatic interleuklin 15 (IL-15) expression: implications for local NK/NKT cell homeostasis and development

Interleukin 15 (IL-15) is critical for the development of human and murine natural killer (NK) cells and hepatic-derived NK T cells (NKT) in mice, and for the homeostatic maintenance of NK/NKT and CD8(+) memory T cells. The lymphocyte repertoire of an adult human liver includes significant populations of NK and NKT-like cells, which may arise locally from hepatic haematopoietic stem cells (HSCs). We investigated hepatic IL-15 levels and the expression of IL-2/IL-15-receptor beta-chain (IL-2/IL-15Rbeta; CD122) on mature hepatic lymphocytes and HSCs. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect secreted/intracellular IL-15 transcripts. IL-15 protein was localized using immunohistochemistry; levels were measured by enzyme-linked immunosorbent assay IL-2/IL-15Rbeta expression by flow-cytometry. Normal hepatic IL-15 protein was detected at 0.43 ng/100 mg total protein (n = 11, range 0.10 ng-0.9 ng). There was a significant increase in HCV-infected tissue (1.78 ng, P < 0.005, n = 11, range 0.18-2.43 ng). The staining pattern suggests that infiltrating monocytes and tissue resident Kupffer cells are the main producers. IL-15 protein was detected in supernatants from cultured liver biopsy specimens in the absence of stimulation (mean 175.8 pg/100 mg wet tissue, n = 3), which increased significantly upon stimulation (P < 0.05, mean 231.21 pg). On average, 61% of hepatic HSCs expressed IL-2/IL-15Rbeta suggesting a local lymphopoietic role. Eighty per cent of NK and 45.8% of CD56(+) T cells expressed IL-2/IL-15Rbeta, suggesting involvement in local CD56(+) cell activation and expansion. Constitutive expression of IL-15 protein and IL-2/IL-15Rbeta on hepatic lymphocytes suggests a key role in the generation and maintenance of the unique hepatic lymphoid repertoire. The significant increase observed in HCV-infected liver suggests a role for IL-15 in host antiviral responses in the liver.

Endogenous IL-15 Sustains Recruitment of IL-2Rβ and Common γ and IL-2-Mediated Chemokine Production in Normal and Inflamed Human Gingival Fibroblasts

We recently reported that anti-IL-15 neutralizing mAb has been shown to inhibit production of MCP-1 in response to IL-2 from normal human gingival fibroblasts (HGF), the major constituent of gingival tissue. In the present study, we examined the expression of IL-2R and IL-15R subunits in HGF from normal and inflamed regions and the role of endogenous IL-15 in IL-2-mediated signaling. Normal HGF expressed IL-2Rbeta and common gamma-chain (gammac) but not IL-2Ralpha or IL-15Ralpha, whereas inflamed HGF expressed IL-2Ralpha, IL-15Ralpha, IL-2Rbeta, and gammac, as assessed by RT-PCR and flow cytometry. Exogenous IL-2 and IL-15 induced production of MCP-1 but not IL-8 in normal HGF, and induced the production of both chemokines in inflamed HGF. Both HGF constitutively transcribed the 48 aa-IL-15 isoform, and the isoform was not actively secreted but rather existed as a membrane-bound form. Pretreatment with anti-IL-15 neutralizing mAb for 24 h completely inhibited the production of MCP-1 induced by IL-2 and IL-15 and IL-2-induced phosphorylation of Jak 1 and 3 in HGF. The pretreatment and RNA interference targeted to IL-15 mRNA resulted in total inhibition of the IL-2Rbeta and gammac expression at mRNA and protein levels. Furthermore, excess amounts of IL-2 restored the inhibitory effect of anti-IL-15, inhibition of NF-kappaB abrogated the expression of IL-2Rbeta and gammac, and IL-2-induced-nuclear translocation of NF-kappaB was completely inhibited by the RNA interference in HGF. These results suggest that endogenous membrane-bound IL-15 sustains recruitment of IL-2Rbeta and gammac through activation of NF-kappaB in HGF.

IL-15 and the initiation of cell contact-dependent synovial fibroblast-T lymphocyte cross-talk in rheumatoid arthritis: effect of methotrexate

To characterize the molecules responsible for synovial fibroblast-T lymphocyte (TL) cross-talk in rheumatoid arthritis (RA), synovial fibroblasts from patients with established RA (RASFibs) were cocultured with TLs from peripheral blood of early RA patients (RAPBTL). TLs from peripheral blood of healthy controls and from synovial fluid of RA served as controls. Adhesion molecules and cytokines were determined by flow cytometry, ELISA, and real-time PCR. RAPBTL (n = 20) induced an up-regulation of ICAM-1, intracellular IL-8, IL-6, IL-15, and surface IL-15 in cocultured RASFibs. In turn, RAPBTL showed an up-regulation of TNF-alpha, IFN-gamma, IL-17, CD25, and CD69 expression. Responses seen with TLs from peripheral blood of healthy controls (n = 20) were significantly lower, whereas responses with TLs from synovial fluid of RA (n = 20) were maximal. Blocking Abs to IL-15 and CD54, but not an isotype-control Ab, down-regulated the increased TL cytokine and activation marker expression. Abs to CD69, CD11a, IL-17, TNF-alpha, and IFN-gamma significantly decreased the up-regulation of RASFib cytokine and CD54 expression. Cocultures using 0.4- micro m inserts did not result in up-regulation of surface molecules or cytokines. Methotrexate significantly inhibited RASFib/TL cross-talk signals and decreased adhesion of TL to RASFibs. In summary, RASFib production of IL-15 induces the proinflammatory cytokines TNF-alpha, IFN-gamma, and IL-17 in cocultured TLs through a cell contact-dependent mechanism. In turn, these cytokines stimulate the expression of IL-15, IL-8, and IL-6 in RASFibs, thereby creating a feedback loop that favors persistent synovial inflammation. Methotrexate seems to disrupt this loop by decreasing cell adhesion.

Monocyte surface-bound IL-15 can function as an activating receptor and participate in reverse signaling

IL-15 is a short chain, four-alpha helix cytokine that shares some biological function with IL-2. One striking difference between IL-2 and IL-15 is the ability of monocytes to express IL-15 on their cell surface after activation. In the current study we have investigated the ability of human monocyte cell surface IL-15 to participate in reverse signaling. Cross-linking anti-IL-15 Abs were used as a surrogate ligand for surface IL-15 engagement. Ligation of cell surface-expressed IL-15 induced monocyte adhesion that required the activity of small m.w. GTPases. Reverse signals through surface IL-15 activated the Rho-GTPase Rac3. In addition, engagement of cell surface IL-15 was found to activate a number of signaling pathways, including both extracellular signal-regulated kinase 1/2 and p38, and resulted in the secretion of IL-8. IL-8 production required mitogen-activated protein kinase activity. Thus, the current study has established that cell surface IL-15 is more than just a ligand; it can function as a receptor and participate in reverse signaling that results in cellular adhesion and production of inflammatory cytokines.