The Immunoregulatory and Regenerative Potential of Activated Human Stem Cell Secretome Mitigates Acute-on-Chronic Liver Failure in a Rat Model

Acute-on-chronic liver failure (ACLF) is a syndrome marked by sudden liver function decline and multiorgan failure, predominantly acute kidney injury (AKY), in patients with chronic liver disease. Unregulated inflammation is a hallmark of ACLF; however, the key drivers of ACLF are not fully understood. This study explores the therapeutic properties of human mesenchymal stem cell (MSC) secretome, particularly focusing on its enhanced anti-inflammatory and pro-regenerative properties after the in vitro preconditioning of the cells. We evaluated the efficacy of the systemic administration of MSC secretome in preventing liver failure and AKI in a rat ACLF model where chronic liver disease was induced using by the administration of porcine serum, followed by D-galN/LPS administration to induce acute failure. After ACLF induction, animals were treated with saline (ACLF group) or MSC-derived secretome (ACLF-secretome group). The study revealed that MSC-secretome administration strongly reduced liver histological damage in the ACLF group, which was correlated with higher hepatocyte proliferation, increased hepatic and systemic anti-inflammatory molecule levels, and reduced neutrophil and macrophage infiltration. Additionally, renal examination revealed that MSC-secretome treatment mitigated tubular injuries, reduced apoptosis, and downregulated injury markers. These improvements were linked to increased survival rates in the ACLF-secretome group, endorsing MSC secretomes as a promising therapy for multiorgan failure in ACLF.

Pathogen-induced tissue-resident memory TH17 (TRM17) cells amplify autoimmune kidney disease

Although it is well established that microbial infections predispose to autoimmune diseases, the underlying mechanisms remain poorly understood. After infection, tissue-resident memory T (T_RM) cells persist in peripheral organs and provide immune protection against reinfection. However, whether T_RM cells participate in responses unrelated to the primary infection, such as autoimmune inflammation, is unknown. By using high-dimensional single-cell analysis, we identified CD4⁺ T_RM cells with a T_H17 signature (termed T_RM17 cells) in kidneys of patients with ANCA-associated glomerulonephritis. Experimental models demonstrated that renal T_RM17 cells were induced by pathogens infecting the kidney, such as Staphylococcus aureus, Candida albicans, and uropathogenic Escherichia coli, and persisted after the clearance of infections. Upon induction of experimental glomerulonephritis, these kidney T_RM17 cells rapidly responded to local proinflammatory cytokines by producing IL-17A and thereby exacerbate renal pathology. Thus, our data show that pathogen-induced T_RM17 cells have a previously unrecognized function in aggravating autoimmune disease.

Thymic B Cells Promote Germinal Center-Like Structures and the Expansion of Follicular Helper T Cells in Lupus-Prone Mice

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the activation of autoreactive T and B cells, autoantibody production, and immune complex deposition in various organs. Previous evidence showed abnormal accumulation of B cells in the thymus of lupus-prone mice, but the role of this population in the progression of the disease remains mostly undefined. Here we analyzed the spatial distribution, function, and properties of this thymic B cell population in the BWF1 murine model of SLE. We found that in diseased animals, thymic B cells proliferate, and cluster in structures that resemble ectopic germinal centers. Moreover, we detected antibody-secreting cells in the thymus of diseased-BWF1 mice that produce anti-dsDNA IgG autoantibodies. We also found that thymic B cells from diseased-BWF1 mice induced the differentiation of thymocytes to follicular helper T cells (T_FH). These data suggest that the accumulation of B cells in the thymus of BWF1 mice results in the formation of germinal center-like structures and the expansion of a T_FH population, which may, in turn, activate and differentiate B cells into autoreactive plasma cells. Therefore, the thymus emerges as an important niche that supports the maintenance of the pathogenic humoral response in the development of murine SLE.

Purinergic Signaling as a Regulator of Th17 Cell Plasticity

T helper type 17 (Th17) lymphocytes, characterized by the production of interleukin-17 and other pro-inflammatory cytokines, are present in intestinal lamina propria and have been described as important players driving intestinal inflammation. Recent evidence, supporting the notion of a functional and phenotypic instability of Th17 cells, has shown that Th17 differentiate into type 1 regulatory (Tr1) T cells during the resolution of intestinal inflammation. Moreover, it has been suggested that the expression of CD39 ectonucleotidase endows Th17 cells with immunosuppressive properties. However, the exact role of CD39 ectonucleotidase in Th17 cells has not been studied in the context of intestinal inflammation. Here we show that Th17 cells expressing CD39 ectonucleotidase can hydrolyze ATP and survive to ATP-induced cell death. Moreover, in vitro-generated Th17 cells expressing the CD39 ectonucleotidase produce IL-10 and are less pathogenic than CD39 negative Th17 cells in a model of experimental colitis in Rag-/- mice. Remarkably, we show that CD39 activity regulates the conversion of Th17 cells to IL-10-producing cells in vitro, which is abrogated in the presence of ATP and the CD39-specific inhibitor ARL67156. All these data suggest that CD39 expression by Th17 cells allows the depletion of ATP and is crucial for IL-10 production and survival during the resolution of intestinal inflammation.

Alloreactive Regulatory T Cells Allow the Generation of Mixed Chimerism and Transplant Tolerance

The induction of donor-specific transplant tolerance is one of the main goals of modern immunology. Establishment of a mixed chimerism state in the transplant recipient has proven to be a suitable strategy for the induction of long-term allograft tolerance; however, current experimental recipient preconditioning protocols have many side effects, and are not feasible for use in future therapies. In order to improve the current mixed chimerism induction protocols, we developed a non-myeloablative bone-marrow transplant (NM-BMT) protocol using retinoic acid (RA)-induced alloantigen-specific Tregs, clinically available immunosuppressive drugs, and lower doses of irradiation. We demonstrate that RA-induced alloantigen-specific Tregs in addition to a NM-BMT protocol generates stable mixed chimerism and induces tolerance to allogeneic secondary skin allografts in mice. Therefore, the establishment of mixed chimerism through the use of donor-specific Tregs rather than non-specific immunosuppression could have a potential use in organ transplantation.

Pro-Inflammatory Cytokines in Nasopharyngeal Aspirate From Hospitalized Children With Respiratory Syncytial Virus Infection With or Without Rhinovirus Bronchiolitis, and Use of the Cytokines as Predictors of Illness Severity

Respiratory syncytial virus (RSV) and human rhinovirus (HRV) respiratory infection in children induce production of inflammatory interleukins (ILs) in the respiratory epithelium. As IL(s) determine the severity of illness, the purpose of this study was to identify the pro-inflammatory IL(s) that could be predictor(s) of clinical severity. One hundred and fifteen patients <2 years old with bronchiolitis due to RSV and /or HRV and 38 controls were selected from a hospital and an outpatient clinic. Clinical data of all patients were recorded. Severity was defined by the number of days with oxygen need. Nasopharyngeal aspirates (NPA) were collected to perform viral diagnosis by quantitative reverse transcription and polymerase chain reaction (qRT-PCR) and to quantify ILs: TNF-α, IL-10, IL-6, IL-1β, and IL-8, by flow cytometry. Simple and multiple regression and receiver operating characteristic (ROC) curves were used for statistical analysis. Of the patients selected 60 were single RSV, 28 RSV associated to HRV, and 27 single HRV. All patients (115) showed significantly higher IL levels when compared with controls. Levels of IL-6, IL-1β, and IL-8 detected in NPA from RSV single and associated to HRV were significantly higher than HRV infected and positively associated with days requiring O2.Levels of IL-6, IL-1β, and IL-8 detected in NPA from patients infected with RSV only or with both RSV and HRV are increased, and any of those 3 cytokines may have a predictive value for the number of days with need of supplemental oxygen.

T helper type 17 cells contribute to anti-tumour immunity and promote the recruitment of T helper type 1 cells to the tumour

T helper type 17 (Th17) lymphocytes are found in high frequency in tumour-burdened animals and cancer patients. These lymphocytes, characterized by the production of interleukin-17 and other pro-inflammatory cytokines, have a well-defined role in the development of inflammatory and autoimmune pathologies; however, their function in tumour immunity is less clear. We explored possible opposing anti-tumour and tumour-promoting functions of Th17 cells by evaluating tumour growth and the ability to promote tumour infiltration of myeloid-derived suppressor cells (MDSC), regulatory T cells and CD4(+)  interferon-γ(+) cells in a retinoic acid-like orphan receptor γt (RORγt) -deficient mouse model. A reduced percentage of Th17 cells in the tumour microenvironment in RORγt-deficient mice led to enhanced tumour growth, that could be reverted by adoptive transfer of Th17 cells. Differences in tumour growth were not associated with changes in the accumulation or suppressive function of MDSC and regulatory T cells but were related to a decrease in the proportion of CD4(+) T cells in the tumour. Our results suggest that Th17 cells do not affect the recruitment of immunosuppressive populations but favour the recruitment of effector Th1 cells to the tumour, thereby promoting anti-tumour responses.

Transplant tolerance: new insights and strategies for long-term allograft acceptance

One of the greatest advances in medicine during the past century is the introduction of organ transplantation. This therapeutic strategy designed to treat organ failure and organ dysfunction allows to prolong the survival of many patients that are faced with no other treatment option. Today, organ transplantation between genetically dissimilar individuals (allogeneic grafting) is a procedure widely used as a therapeutic alternative in cases of organ failure, hematological disease treatment, and some malignancies. Despite the potential of organ transplantation, the administration of immunosuppressive drugs required for allograft acceptance induces severe immunosuppression in transplanted patients, which leads to serious side effects such as infection with opportunistic pathogens and the occurrence of neoplasias, in addition to the known intrinsic toxicity of these drugs. To solve this setback in allotransplantation, researchers have focused on manipulating the immune response in order to create a state of tolerance rather than unspecific immunosuppression. Here, we describe the different treatments and some of the novel immunotherapeutic strategies undertaken to induce transplantation tolerance.

Retinoic acid generates regulatory T cells in experimental transplantation

Regulatory T cells play a key role to inhibit effector lymphocytes, avoid, autoimmunity, and restrain allogeneic immunity. Retinoic acid is an important cofactor that stimulates the generation and expansion of regulatory T cells. Naive T cells, coincubated with allogeneic antigen-presenting cells and retinoic acid, in conjunction with transforming growth factor (TGF) β and interleukin (IL) 2, generated allogeneic regulatory T cells de novo. These cells were able to inhibit skin rejection in adoptive transfer experiments. The generation of regulatory T cells ex vivo with retinoic acid, TGF-β, and IL-2 represents a new step toward specific regulation of allogeneic immune responses.

Delivery of alloantigens via apoptotic cells generates dendritic cells with an immature tolerogenic phenotype

BACKGROUND

Dendritic cells (DCs) are professional antigen-presenting cells able to induce immunity or tolerance. The interactions of immature DCs with naive T lymphocytes induce peripheral tolerance through mechanisms that include anergy or deletion of lymphocytes or the generation of regulatory T cells. Because of the central role of DCs in the immune response, they are potential targets for the induction of experimental tolerance. Thus, the generation of immature (tolerogenic) DCs able to capture and present alloantigens to T cells represents an important aim in our efforts to achieve better transplant acceptance.

METHODS

In this work, we generated immature DCs by using vitamin D(3) (VD3) during the process of DC differentiation.

RESULTS

The VD3-DCs showed an immature phenotype characterized by a low expression of major histocompatibility complex antigens of class II, CD86, and CD80 molecules and the secretion of a tolerogenic cytokine pattern. Furthermore, we showed that VD3-DCs phagocytose apoptotic allogeneic cells efficiently without inducing DC maturation or activation. Most important, our experiments demonstrated that mice treated with VD3 produce immature DCs in vivo, and that DCs from VD3-treated mice immunized with allogeneic apoptotic cells maintained their tolerogenic phenotype.

CONCLUSION

Our results show that allogeneic apoptotic cells in combination with VD3 generate DCs with tolerogenic characteristics that could be used to induce tolerance towards alloantigens.

Differential regulation of Notch ligands in dendritic cells upon interaction with T helper cells

The Notch signalling pathway has recently been linked to T helper 1 (Th1)/T helper 2 (Th2) cell polarization via a mechanism involving differential expression of Notch ligands, Delta-like and Jagged, in antigen-presenting cells. However, whether stimuli other than pathogen-derived factors are involved in the regulation of Notch ligand expression in dendritic cells (DCs) remains unknown. Here, we address the effect of T helper cells (Th1 and Th2) on Delta-like 4 and Jagged 2 expression in bone marrow-derived DCs. We demonstrate that both Th1 and Th2 cells induce Delta-like 4 mRNA expression in DCs, in a process that is, in part, mediated by CD40 signalling. In contrast, only Th2 cells induce a significant increase in Jagged 2 mRNA levels in DCs. Additionally, we show that IL-4, a hallmark Th2 cytokine, plays a role in Jagged 2 expression, as evidenced by the fact that cholera toxin, a Th2-promoting stimulus, induces Jagged 2 mRNA expression in DCs only in the presence of IL-4. Finally, we demonstrate that DCs also express Notch 1 and that this expression is downregulated by IL-4. These data suggest that Notch ligands are differentially regulated in DCs: Delta-like 4 is regulated by T helper cells and by pathogen-derived Th1 stimuli, whereas Jagged 2 is regulated by Th2 cells and pathogen-derived Th2-promoting stimuli. Based on our results, we propose that the positive feedback loop that Th2 cells exert on T cell polarization may involve the induction of Jagged 2 expression in DCs.

MyD88 and retinoic acid signaling pathways interact to modulate gastrointestinal activities of dendritic cells

BACKGROUND & AIMS

Gut-associated dendritic cells (DC) metabolize vitamin A into all-trans retinoic acid (RA), which is required to induce lymphocytes to localize to the gastrointestinal tract and promotes the differentiation of Foxp3+ regulatory T cells and IgA antibody-secreting cells. We investigated whether RA functions in a positive-feedback loop in DC to induce its own synthesis.

METHODS

We measured levels of retinoids in intestinal tissues from mice and assessed the role of RA in the functional specialization of gut-associated DC in cell cultures and mice. We used pharmacologic antagonists to determine the signaling pathways involved in regulation of DC and used MyD88-/- mice to determine the contribution of Toll-like receptor signaling in RA-mediated effects on DC.

RESULTS

The concentration of retinoids decreased in a proximal-to-distal gradient along the intestine, which correlated with the activity of gut-specific DC. Importantly, RA regulated the ability of gut-associated DC to produce RA, induce T cells to localize to the gastrointestinal tract, and generate regulatory T cells and IgA-secreting cells. RA was sufficient to induce its own production by extraintestinal DC in vitro and in vivo. RA-mediated regulation of DC required signaling through the mitogen-activated protein kinase signaling pathway and unexpectedly required MyD88, which is conventionally associated with Toll-like receptor, interleukin-1, and interleukin-18 signaling.

CONCLUSIONS

RA is necessary and sufficient to induce DC to regulate T-cell localization to the gastrointestinal tract and IgA secretion. Our findings also indicate crosstalk between the RA receptor and MyD88-dependent Toll-like receptor signaling pathways.

Dendritic cells and B cells cooperate in the generation of CD4(+)CD25(+)FOXP3(+) allogeneic T cells

BACKGROUND

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) play an essential role in immune tolerance, suppressing responses against self-antigens. Additionally, Treg play an important role in maintaining immunosuppression to alloantigens as well as to other antigens. It is well known that in the gut, a subset of dendritic cells produces retinoic acid (RA), which together with transforming growth factor (TGF-beta) is able to differentiate naïve T cells into Treg. The aim of this study was to establish the role of antigen-presenting cells (APC) in the differentiation of allogeneic Tregs under the effect of RA and TGF-beta.

METHODS

Splenic CD4(+)CD25(-) naïve T cells from C57BL/6 mice were co-cultured with splenic CD11c-enriched APC from Balb/c mice in the presence of TGF-beta, RA, and interleukin (IL-2). After 6 days of culture, cells were analyzed for the expression of Foxp3 by flow cytometry. Additionally, we investigated the role of B cells and dendritic cells (DCs) and their stimulatory capacity in the generation of Tregs.

RESULTS

Our results showed that co-culture of naive T cells with the appropriate level of stimulation by APC in the presence of TGF-beta, RA, and IL-2 provided a new powerful approach to generate allogeneic Treg cells. We demonstrated that although B cells and DCs can generate Tregs by themselves, a mixure of both APC improved their capacity to efficiently generate Tregs. Also, we observed that although the addition of IL-2 to the cultures was not crucial to generate Tregs, it was required to optimize their expansion and cell survival.

Transforming growth factor-beta and all-trans retinoic acid generate ex vivo transgenic regulatory T cells with intestinal homing receptors

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) mediate immunologic self-tolerance and suppress immune responses. In the gut, a subset of dendritic cells is specialized to induce Treg in a transforming growth factor-beta (TGF-beta)- and retinoic acid (RA)-dependent manner. The aim of this study was to establish if RA synergizing with TGF-beta induced antigen specific CD4(+) CD25(high) Foxp3(+) Treg portraying gut homing receptors. Splenic CD4(+)CD25(-) Foxp3(-) naïve T cells from DO11.10 mice were cocultured with splenic CD11c(+) dendritic cells from Balb/c mice in the presence of TGF-beta, RA, and low levels of an antigenic peptide. After 5 days of culture, cells were analyzed for the expression of Foxp3 and the gut homing receptors CCR9 and alpha4beta7. The number of Foxp3(+) T cells generated with TGF-beta and RA was at least 3 times higher than in the cultures with TGF-beta alone and 15 times higher than in controls without exogenous cytokines. Also, supplementation of the cultures with RA induced the expression of the intestinal homing receptors CCR9 and alpha4beta7. Our results showed that coculture of naïve T cells with antigen-presenting cells in the presence of TGF-beta and RA represents a powerful approach to generate Treg with specific homing receptors.

Alemtuzumab induction in kidney transplantation: clinical results and impact on T-regulatory cells

Alemtuzumab (ALT), a humanized monoclonal anti-CD52 antibody, was introduced in solid organ transplantation as an induction agent. ALT associated with anticalcineurins has provided a low incidence of acute rejection episodes (ARE) and potential tolerogenic properties. We analyzed the clinical outcomes and effects on peripheral Treg of renal transplant recipients treated with ALT. Six-month data on kidney alone or kidney combined with pancreas or liver patients treated with ALT and tacrolimus (TAC) in standard doses were compared with those on renal transplant recipients of similar demography who were not treated with ALT. We evaluated patient and graft survivals, ARE incidence, hematological parameters, renal function, adverse events, and CD4+CD25+FoxP3+ T cells in peripheral blood. Demographics of recipients, donors, and transplants were similar in both groups. Mean HLA mismatch was slightly greater among ALT-treated patients (3.5 vs 2.5). No combined transplantation was performed in the ALT-untreated group. Patient and graft survivals were 100% without rejection or serious infections in both groups. ALT-treated recipients showed anemia and leukopenia in 3 patients as well as severe lymphopenia in 5 recipients, who partially recovered on day 90. Final mean plasma creatinine was 1.4 mg/dL, while calculated creatinine clearance was approximately 65 mL/min in both groups. Mean Treg cell percentage was higher among ALT-treated recipients than the comparative group or healthy controls (P < .05). In conclusion, renal transplantation results obtained using ALT with rigorous immunosuppressive therapy were excellent; serious adverse events and acute rejection were absent. The effect of the increased proportion of Treg cells must be evaluated with longer observation.

Generation of Dendritic Cells With Regulatory Properties

Dendritic cells (DCs) are professional antigen presenting cells with the ability to induce and regulate an immune response. DCs that capture and present antigen under noninflammatory conditions maintain an immature phenotype and acquire tolerogenic properties. These DCs generate regulatory T lymphocytes that potentiate tolerogenic responses. Here we developed a method for the generation of immature murine DCs able to process and present a specific antigen in a tolerogenic context. Immature DCs were prepared from bone marrow precursors after differentiation with granulocyte-macrophage colony-stimulating factor (GM-CSF) in the presence of vitamin D(3) and characterized by their low expression of major histocompatibility complex class (MHC) II and CD86 molecules. Purified phagosomes containing either MHC II molecules or ovalbumin were used to deliver antigens to immature DCs. More than 80% of the DCs captured the phagosomes, while maintaining a low expression of maturation markers and showing basal levels of secretion of activating cytokines such as interleukin (IL)-2 and IL-12. Treatment of the immature DCs with lipopolysaccharides (LPS) increased IL-10 secretion, in agreement with their anti-inflammatory and immune regulatory properties. Cocultures of transgenic OT-II T lymphocytes with the immature DCs carrying OVA-phagosomes succeeded in generating a subpopulation of regulatory T lymphocytes characterized by the expression of CD4, CD25, CD62L, and Foxp3. Taken together, our results suggest that vitamin D(3) generates immune tolerance through the modulation of DC phenotype and could be useful to induce tolerance to allotransplants.

Cyclosporine preconditions dendritic cells during differentiation and reduces IL-2 and IL-12 production following activation: a potential tolerogenic effect

The mode of action of cyclosporine (CsA) has been ascribed to its capacity to inhibit IL-2 and IFNgamma production by T cells, two cytokines implicated in allograft rejection. Recently, it has been reported that upon activation, dendritic cells (DCs) exhibit transient production of IL-2, a property that appears to be related to their capacity to initiate immune responses. On the other hand, DCs can generate signals determining Th1/Th2 polarizing effects, an effect that can drastically influence the outcome of organ transplant. The purpose of the present study was to investigate the effect of CsA on cytokine production by immature and mature DCs. DC precursors from mouse bone marrow were induced to differentiate by incubation with GM-CSF for 5 days followed by activation with LPS for 4 hours. CsA was added at different times during this process. Our results show that when CsA is added during the differentiation period following activation with LPS, IL-2 and IL-12 secretion are significantly reduced without affecting the evolution of the DC. Conversely, CsA had no effect when added during the LPS activation period. These results show that CsA affects DCs before they receive the final activation stimulus, preconditioning them to antigen stimulation. This preconditioning of DCs by calcineurin-inhibiting drugs conceptually integrates the mode of action of CsA with the tolerogenic and T-cell polarization function ascribed to DCs. These results may be especially meaningful for the future design of immunosuppressive protocols.

Interleukin-4 Selectively Inhibits Interleukin-2 Secretion by Lipopolysaccharide-Activated Dendritic Cells

Dendritic cells (DCs) generated in vitro from bone marrow precursors using granulocyte-macrophage colony-stimulating factor (GM-CSF) secrete interleukin-2 (IL-2) upon activation, an event probably associated to the initiation of adaptive immune responses. Additionally, they produce IL-12, a cytokine related to T-cell polarization. To analyse the effect of IL-4 on DC differentiation and function, we assessed the capacity of murine bone marrow dendritic cells (BMDCs) differentiated with GM-CSF in the presence or absence of IL-4 to produce IL-2 and IL-12 upon lipopolysaccharide (LPS) activation. We found that although IL-4 enhanced DC IL-12p70 production, it strongly impaired IL-2 secretion by BMDCs. This inhibition, which depends on the presence of IL-4 during LPS activation, is DC specific, as IL-4 did not affect IL-2 secretion by T cells. Interestingly, inhibition of DC IL-2 production did not prevent DC priming of T lymphocytes. These results illustrate a new putative role for IL-4 on the regulation of the immune response and should help clarify the controversial reports on the effect of IL-4 on DCs.

Selective imprinting of gut-homing T cells by Peyer's patch dendritic cells

Whereas naive T cells migrate only to secondary lymphoid organs, activation by antigen confers to T cells the ability to home to non-lymphoid sites. Activated effector/memory T cells migrate preferentially to tissues that are connected to the secondary lymphoid organs where antigen was first encountered. Thus, oral antigens induce effector/memory cells that express essential receptors for intestinal homing, namely the integrin alpha4beta7 and CCR9, the receptor for the gut-associated chemokine TECK/CCL25 (refs 6, 8, 9). Here we show that this imprinting of gut tropism is mediated by dendritic cells from Peyer's patches. Stimulation of CD8-expressing T cells by dendritic cells from Peyer's patches, peripheral lymph nodes and spleen induced equivalent activation markers and effector activity in T cells, but only Peyer's patch dendritic cells induced high levels of alpha4beta7, responsiveness to TECK and the ability to home to the small intestine. These findings establish that Peyer's patch dendritic cells imprint gut-homing specificity on T cells, and thus license effector/memory cells to access anatomical sites most likely to contain their cognate antigen.

MHC class II-deficient tumor cell lines with a defective expression of the class II transactivator

MHC class II expression defects have been evidenced in several human tumor cell lines originating from lung cancers or retinoblastoma. Accordingly, the mouse adenocarcinoma and fibrosarcoma cell lines, RAG and L(tk-), do not express I-A and I-E molecules even when treated with IFN-gamma. Here we show that fusion of both cell lines restores the inducible expression of MHC class II, thereby demonstrating that they present different and recessive alterations outside the MHC class II locus. CIITA, the MHC class II transactivator, controls the tissue-specific expression of MHC class II genes and creates the architecture of the transcriptional complex that binds to the MHC class II gene promoters. In L(tk-) cells, C2ta transcripts, expressed from the gene encoding CIITA, were indeed detected in severely limited amounts, with a defect in C2ta transcription initiation. In agreement we show here that the L(tk-) cell line does not express the CIITA protein. In contrast, in the RAG cell line, C2ta transcripts were expressed at normal levels, from the proper initiation site. The nucleotide sequencing of the CIITA cDNA from RAG did not reveal any mutation. However, the CIITA protein was not detected. These data evidence a new type of defect in a MHC class II-defective tumor cell line, as we show here that the alteration in the RAG cells occurs downstream of C2ta transcription. The RAG mutation might therefore reside in the C2ta transcript nuclear export or translation, or in the stability of the CIITA protein.

Expression of the human SRY protein during development in normal male gonadal and sex-reversed tissues

Sex determination in mammals is controlled by the SRY gene located on the Y chromosome. It encodes a protein containing a DNA-binding and DNA-bending domain. In spite of recent advances in the identification of the mechanisms that regulate male sex determination in mammals, the expression profile of the SRY protein in normal and sex-reversed human tissues is not well established. In order to localize the SRY protein and determine its cellular distribution and expression at different stages of development, we prepared monoclonal antibodies (mAb) against the recombinant SRY protein. One of these antibodies, LSRY1.1, recognizes a protein of 27 kDa in total lysates of HeLa SRYB3, a human cell line transfected with the SRY gene under the control of the SV40 promoter. Immunocytochemical analysis in the cell lines shows nuclear localization of the SRY protein. We have studied SRY protein expression in human tissues at different stage of fetal development until adult life and have demonstrated that the SRY protein is located in the nuclei of somatic cells and germ cells in the genital ridge during testis development. After testis determination, it can be detected until the adult stage in both germ cells and Sertoli cells. The presence of the SRY protein was also analyzed in biopsies of gonadal tissues of sex-reversal patients such as SRY-positive 46,XX males or SRY-positive 46,XX true hermaphrodites. SRY protein is detected in the nuclei of Sertoli cells of the testis and in the nuclei of granulosa cells in the ovotestis in these patients and in the nuclei of germ cells of both tissue types. These results suggest a common cellular origin for both Sertoli cells and granulosa cells.

Increased expression of c-rel, from the NF-kappaB/Rel family, in T cells from patients with systemic lupus erythematosus

OBJECTIVE

To explore the role of the NF-kappaB/Rel transcription factor family in autoimmunity, we investigated whether peripheral blood mononuclear cells (PBMC) and T cells from the blood of patients with systemic lupus erythematosus (SLE) exhibit abnormal expression of c-rel, both when recently isolated and/or during in vitro activation.

METHODS

Total RNA and protein extracts were prepared from PBMC and T cells isolated by immunoadsorption with magnetic beads. The relative concentrations of c-rel mRNA and of c-Rel protein were determined by semiquantitative assays of competitive reverse transcriptase-polymerase chain reaction and chemiluminescent immunoblots, respectively. Activity of NF-kappaB/Rel was studied by electrophoretic mobility shift assay of nuclear extracts.

RESULTS

Significantly increased levels of c-rel mRNA were found (1) in PBMC from SLE patients (n = 48; p<0.0000001), even during inactive disease (n = 11; p<0.001), compared to controls (n = 54), and (2) in T cells isolated from a subgroup of these patients (n = 11; p<0.00002) and controls (n = 12). c-Rel protein was found increased in the cytosol but not in the nucleus of PBMC of patients with SLE (n = 12; p<0.02) compared to controls (n = 12). No evidence of NF-kappaB/Rel nuclear activity was detected. In vitro stimulation of T cells by incubating PBMC with concanavalin A showed that less c-Rel entered the nucleus in lupus cells than healthy cells, correlating with lower interleukin 2 production. However, the same stimulating conditions provoked an increase in c-rel mRNA to higher levels in lupus cells from 2 patients compared with 2 controls. Increased levels of both IkappaB alpha and IkappaB beta could account for c-Rel cytosolic retention.

CONCLUSION

Our data suggest that T cells from patients with SLE possess altered regulatory mechanisms of c-rel expression and nuclear import that might potentially determine conditions for developing autoimmunity. Other cells present in the PBMC could also be affected.

The human SRY protein is present in fetal and adult Sertoli cells and germ cells

Sex determination in mammals is controlled by the Y chromosome located SRY gene. Despite recent advances towards understanding the mechanisms that regulate sex determination in mammals, the expression profile of the SRY protein in human tissues is unknown. To localize the SRY protein and determine its cellular distribution, we prepared monoclonal antibodies (mAb) against the recombinant SRY protein. One antibody, LSRY1.1, recognizes a SRY-specific epitope and was used to localize the protein in different cells and tissues. The mAb recognizes a protein of 27 kDa in total lysates of HeLa SRYB3 cells. Immunocytochemical staining showed a nuclear localization of the protein. Immunohistochemical studies performed on gonadal tissue of a fetus, a one month-old boy and an adult man, demonstrated the presence of SRY protein in the nucleus of Sertoli and germ cells. In addition two 46,XX SRY(+) males had the SRY protein in their gonadal tissues. All other samples were negative, including all female tissue studied and the testis of a 46,XX SRY(-) male. The presence of SRY protein in fetal and adult gonadal tissues including germ cells suggests that SRY may have other male-specific functions in addition to sex determinism.

A flow cytometric procedure for the quantification of cell adhesion in complex mixtures of cells

We present a simple non-radioactive cytometry-based assay that permits the simultaneous quantitation of cell adhesion of distinct subsets of cells contained in a mixture without any previous fractionation. The procedure is simple and highly reproducible and has the advantage of confining the quantitation of cell adhesion to live cells only. This new approach is based on counting the absolute number of cells. This is done by adding known numbers of distinguishable beads to the cell suspension and counting beads and cells in a cytometer. Quantitation of adhesion is accomplished by counting each subpopulation of cells before and after the adhesive process. To illustrate this methodology we determined adhesion of Ramos cells to monolayers of endothelial cells and its inhibition by specific antibodies. Also, we determined adhesion to endothelial cells of B lymphocytes and subsets of T lymphocytes present in a preparation of unfractionated human mononuclear cells. The results presented here demonstrate that the new assay has the required properties to be used in the quantitation of cell adhesion.

CIITA B-cell-specific promoter suppression in MHC class II-silenced cell hybrids

In this study, various sets of somatic cell hybrids, generated by the fusion of epithelial cell lines with B-lymphoblastoid cell lines, were analyzed for the expression of major histocompatibility complex (MHC) class II antigens. We first demonstrate, in human and mouse intraspecies hybrids, the coordinate suppression of MHC class II, Ii (invariant chain) and HLA-DM gene transcription, and the release of the silencing by the addition of interferon gamma. Using interspecies hybrids, the segregation of human chromosomes allowed us to establish that MHC class II extinction is linked to the presence in the hybrids of the chromosomes from the epithelial fusion partner. Moreover, our data provide evidence that the expression pattern of MHC class II mRNA is correlated with that of the class II transactivator (CIITA), suggesting that CIITA is the actual target of the silencing. To gain further insight into the suppression phenomenon we performed luciferase assays which show that silencing affects the activity of the B-cell-specific promoter of CIITA. These results therefore demonstrate that the MHC class II gene silencing in somatic cell hybrids is due to an active suppression of one of the promoters of the CIITA gene, mediated by the epithelial cell fusion partner.

Outward currents in Drosophila larval neurons: dunce lacks a maintained outward current component downregulated by cAMP

Outward current modulation by cAMP was investigated in wild type (wt) and dunce (dnc) Drosophila larval neurons. dnc is deficient in a cAMP phosphodiesterase and has altered memory. Outward current modulation by cAMP was investigated by acute or chronic exposure to cAMP analogs. The analysis included a scrutiny of outward current modulation by cAMP in neurons from the mushroom bodies (mrb). In Drosophila, the mrb are the centers of olfactory acquisition and retention. Based on outward current patterns, neurons were classified into four types. Downmodulation of outward currents induced by acute application of cAMP analogs was reversible and found only in type I and type IV neurons. In the general wt neuron population, approximately half of neurons exhibited cAMP-modulated, 4-aminopyridine (4-AP)-sensitive currents. On the other hand, a significantly larger fraction of mrb neurons in wt (70%) was endowed with cAMP-modulated, 4-AP-sensitive currents. Only 30% of the dnc neurons displayed outward currents modulated by cAMP. The deficit of cAMP-modulated outward currents was most severe in neurons derived from the mrb of dnc individuals. Only 4% of the mrb neurons of dnc were cAMP-modulated. The dnc defect can be induced by chronic exposure of wt neurons to cAMP analogs. These results document for the first time a well defined electrophysiological neuron phenotype in correlation with the dnc defect. Moreover, this study demonstrates that in dnc mutants such a deficiency affects most severely neurons in brain centers of acquisition and retention.

Spleen-derived stromal cells. Adhesion molecules expression and lymphocyte adhesion to reticular cells

The final steps of lymphocyte differentiation occur in secondary lymphoid organs where B and T lymphocytes interact with the lymphoid microenvironment. Although numerous studies describe the interactions of murine lymphocytes with dendritic, follicular and other antigen presenting cells, little is known on the interactions between lymphocytes and reticular cells, an important cellular component of spleen stroma. In this work we describe the culturing of complete murine spleen stromas and of two cell lines, Sp-1 and Sp-2, identified as of possible reticular origin, and describe the adhesive interactions between murine lymphocytes and human lymphoid cells with murine spleen stromal cells. FACS analysis indicates that the Sp-1 cell line shows a single cell type expressing VCAM-1 and CD44 constitutively. They do not express any of the markers described for follicular cells, interdigitating cells, macrophages or endothelial cells. Our data suggests that these cells represent a population of spleen reticular cells. The Sp-2 cell line shows two phenotypically different cell types that grow in association. FACS analysis demonstrates that both cell types express VCAM-1 and CD44 constitutively, but that they can be differentiated by the expression of CD11b and FcR. These data suggest that the Sp-2 cell line is composed of one type of stromal cell growing over an adherent layer of reticular cells. Furthermore, analysis of the non-B non-T cell fraction prepared from murine spleen shows that approximately 30% of these cells correspond to the CD44/VCAM-1 double positive cells. Murine B and T cells adhere to the complete stromas and to Sp-1 and Sp-2 cell lines. Activation of B cells with LPS had no effect on binding while binding of T cells to complete stromas increased up to threefold after Con-A treatment. Adhesion of human lymphoblastoid Daudi cells to complete spleen stromas is blocked by an anti-(murine) VCAM-1 antibody but not by an antibody to the (human) integrin alpha 4 subunit, while adhesion to the Sp-1 and Sp-2 stromas is blocked by antibodies against both molecules. Also, adhesion of Ramos cells to Sp-2 stromas is inhibited by antibodies to the integrin alpha 4 subunit and to murine VCAM-1. Antibodies to other adhesion receptors such as the integrin beta 2 subunit, ICAM-1 or CD44 have no effect on human cell binding to these stromas. Our results suggest that we have isolated a fraction of splenic reticular cells and that these cells can be cultured as a distinct cell line. The finding that these cells express CD44 and VCAM-1 constitutively and use some of these molecules for lymphocyte binding suggests that spleen reticular cells may be involved in the regulation of normal lymphocyte traffic through the spleen.

Lymphocyte adhesion to endothelium derived from human lymphoid tissue

The development of an efficient immune response depends on the capacity of antigen-specific lymphocytes to migrate into secondary lymphoid organs. The first step in the process of lymphocyte extravasation involves lymphocyte binding to the vascular endothelium. Although several adhesion receptors have been implicated in the migration of lymphocytes to inflamed tissue, their role in the extravasation of these cells to normal lymphoid organs is not yet clearly established. The involvement of adhesion molecules in lymphocyte entrance to secondary lymphoid organs can be better assessed in an in vitro system using endothelial cells in culture. Here we report on the isolation and culture of a homogeneous population of adherent cells of endothelial origin derived from human tonsils (TEC) and on adhesion studies performed with these cells. Beginning from primary cultures of human tonsils, we isolated a population of cells that we show by FACScan analysis to present the intracellular endothelial cell marker Von Willebrand factor and LVAP-2, a surface molecule present in venules from lymphoid organs. The cells are negative for FDC, IDC and macrophage markers. They express ICAM-1, VCAM-1 and CD40 both constitutively and in inducible forms and are induced by IFN-gamma to express major histocompatibility complex class II antigens. As opposed to endothelial cells from human umbilical cord (HUVEC), they do not need to be activated by cytokines to bind lymphoid cells via VLA-4. The mAb HP2/1 directed to the integrin VLA-4 blocks adhesion of Ramos and Daudi cells to tumor necrosis factor alpha (TNF-alpha)-treated HUVEC and to untreated TEC but not of tonsil-derived MNC. On the other hand, an anti-VCAM-1 antibody that blocks adhesion of Ramos and Daudi cells to TNF-alpha-treated HUVEC, does not block adhesion of these cells to TEC, suggesting the presence on the tonsillar endothelial cells of a ligand for VLA-4 different from VCAM-1. We show here that this ligand is not fibronectin.

Transfer of yeast artificial chromosomes into mammalian cells and comparative study of their integrity

Yeast artificial chromosomes (YACs) from the CEPH MegaYAC library (Paris, France) ranging in size from 350 to 1600 kb and mapping to the q22.1 and q22.2 regions of human chromosome 21 were transferred into mammalian cells by spheroplast fusion. The integrity of the YACs from two adjacent parts of the region was compared after retrofitting and stable transfer into mammalian cells. We found that large YACs could easily be manipulated to allow transfer of the YAC material into mammalian cells and that the size of the YAC did not appear to be limiting for fusion. However, we show that there was great variability in the integrity of the YACs from the two regions, which was not related to the size of the YACs. Four YACs in region I from sequence-tagged site (STS) G51E05 up to STS LL103 showed, in general, no loss of material and correct gene transfer into mammalian cells. In contrast, the three YACs in the more centromeric region II (from STS G51B09 up to G51E05) frequently showed a loss of human material during handling, retrofitting and transfer. As a YAC from another library covering region II was also found to be unstable, we propose that the integrity of the YACs is highly dependent on the incorporated human chromosomal DNA.

The recombinant human interferon-gamma receptor is fully functional in a human x murine hybrid containing human chromosome 21

It has previously been shown that stimulation of class I MHC antigen expression by human interferon gamma (Hu-IFN gamma) depends on the presence of both human chromosomes 6 and 21. Even although the presence of human chromosome 6 results in normal expression of the IFN gamma receptor on the cell surface, chromosome 21 is required for this biological response. Here, we transfected the cDNA encoding the Hu-IFN gamma receptor into a mouse cell line, L(tk-), and into a mouse x human hybrid, GM08, containing the human chromosome 21 as the only human genetic material. Two clones, L-gamma R.8 and GM08-gamma R.9, were tested for different biological responses to Hu-IFN gamma. Only the hybrid containing the human chromosome 21 (GM08-gamma R.9) exhibited a biological response when assayed for the stimulation of murine class I MHC antigen expression by Hu-IFN gamma. Moreover, transcriptional induction of 2'-5'-oligoadenylate synthetase and 1-8 genes, as well as antiviral protection, were observed only in the GM08-gamma R.9 transfectants. These results show that human chromosome 21 encodes a factor which mediates different biological activities of Hu-IFN gamma.

Human chromosome 16 encodes a factor involved in induction of class II major histocompatibility antigens by interferon gamma

Interferon gamma (IFN-gamma) induces expression of class II major histocompatibility complex (MHC)-encoded antigens in immunocompetent cells. To gain further insight into the mechanism of this induction, we prepared somatic cell hybrids between different human cell lines and a murine cell line, RAG, that does not express murine class II MHC antigens before or after treatment with murine IFN-gamma. Some of the resulting cell hybrids express murine class II MHC antigens when treated with murine IFN-gamma. This inducible phenotype is correlated with the presence of human chromosome 16. It has been shown previously that the induction of class I MHC antigens by human IFN-gamma in human-rodent hybrids requires the presence of species-specific factors encoded by chromosome 6, which bears the gene for the human IFN-gamma receptor, and chromosome 21, whose product(s) is necessary for the transduction of human IFN-gamma signals. In this report, we show that the induction of murine class II MHC antigens by human IFN-gamma in the human-RAG cell hybrids requires, likewise, the presence of human chromosomes 6 and 21, in addition to chromosome 16. In some of these hybrids, when all three of these human chromosomes were present, induction of cell-surface HLA-DR antigens was also observed. Our results demonstrate that human chromosome 16 encodes a non-species-specific factor involved in the induction of class II MHC antigens by IFN-gamma.

Characterization of human IFN-gamma response using somatic cell hybrids of hematopoietic and nonhematopoietic origin

A panel of 27 rodent-human somatic cell hybrids composed of cells of hematopoietic (nonadherent cells) and nonhematopoietic origin (adherent cells) was used to identify the chromosomes involved in the biological response to human IFN-gamma (Hu-IFN-gamma). We found that the stimulation of class-I histocompatibility antigen expression correlates with the presence of human chromosomes 6 and 21 in adherent cell hybrids, while human chromosome 6 alone is sufficient in nonadherent hybrids. Scatchard analysis of the binding of radiolabeled Hu-IFN-gamma to nonadherent cell hybrids gave a Kd value similar to that found on human cell lines. Induction of a reporter gene placed under the transcriptional control of the interferon responsive sequence (IRS) in adherent cell hybrids requires both chromosomes 6 and 21. The antiviral protection by Hu-IFN-gamma in adherent cell hybrids was reached at physiological doses (2 units/ml) when human chromosomes 6 and 21 were present, while higher doses of Hu-IFN-gamma (5000 units/ml) were required for hybrids lacking chromosome 21. Thus, we demonstrate that differences exit in the response to Hu-IFN-gamma depending on the origin of the cell type.

Blocking of human T lymphocyte activation by channel antagonists

It has been established that early events in lymphocyte activation involve a rise in intracellular Ca++ as well as changes in the flux of other ions. Although a Ca++ channel has been postulated to participate in the early Ca++ rise, its presence in lymphocytes remains controversial. Also although yet undetected, electrophysiological data suggest the presence of a Ca++ activated K+ channel on human peripheral blood lymphocytes (HPBL). Here we report on the effect of specific channel blockers as an approach to the identification of these channels on HPBL. At 40 nM nifedipine, an inhibitor of voltage-gated Ca++ channels, fully inhibits the PHA-promoted activation of HPBL. This effect is concentration dependent with a half maximum effect at approximately 10 nM and is demonstrable whether the drug is added at the same time as or up to 18 h after the addition of the mitogen. This inhibition of activation is not seen if the lymphocytes are activated using IL-2 instead of PHA. Charybdotoxin a toxin which blocks a Ca++ activated K+ channel of muscle cells also blocks to almost 100 per cent the PHA-induced activation of HPBL. This inhibition can be demonstrated regardless of whether the blocker is added together with or up to 4 h after PHA. As opposed to nifedipine charybdotoxin shows no effect if added 18 h after the initiation of the activation process. When nifedipine and charybdotoxin were tested on mice splenocytes we found that nifedipine fully inhibits the LPS-promoted activation of these cells while charybdotoxin has no effect on their activation.(ABSTRACT TRUNCATED AT 250 WORDS)

NH2-terminal sequence of the alpha and beta chains of human DC-1 antigen isolated from the JY cell line. Homology with murine I-A molecules

The DC-1 antigen has been isolated from the JY cell line (DR4, w6). The amino terminal sequences of its alpha and beta chains are both reported and are homologous to the murine I-A antigens. The JY and previously reported LB DC-1 alpha chain sequences appear to be variants of the DC alpha chains reported by other authors. The JY DC-1 beta chain sequence appears to be identical with that deduced from a beta chain cDNA clone and thus identifies this clone. The JY and LB DC-1 beta-chains are clearly different since the latter has a blocked amino terminus.

A homozygous human cell line contains three subsets of HLA-DR-like antigens distinguishable by amino acid sequencing

The major histocompatibility complex (HLA in humans) contains a relatively large set of gene loci in the HLA-D/DR region responsible for regulation of the immune response. The structural dissection of the protein products of these loci is a necessary accompaniment to understanding of this response. In this study, two subsets of HLA-DR-like molecules have been separated by using monoclonal antibodies, and their component alpha and beta chains have been subjected to amino acid terminal sequencing. The results from this sequencing experiment show three differences in the first 14 residues of the beta chains and no differences in the first 15 residues of the alpha chains. These data along with previous sequencing of the DC-1 antigen [Bono, M. R., & Strominger, J. L. (1982) Nature (London) 299, 836-838] demonstrate that three distinct subsets of HLA-DR-like antigens are expressed by a homozygous human lymphoblastoid cell line.

Direct evidence of homology between human DC-1 antigen and murine I-A molecules

The nature of the interactions between cells of the immune system has been shown to be directly related to a group of antigens present on the surface of B lymphocytes. These antigens are under genetic control of the HLA-D/DR region of the human major histocompatibility complex (MHC) located on chromosome 6. DR antigens (the products of the HLA-DR locus within this region), have been defined by serological studies. Recently another antigen, DC-1, has been serologically defined. In the mouse, the I region, analogous to the HLA-D/DR region in man, has been subdivided into at least five subregions (A, B, J, E and C) and specific functions and cell populations associated with each of the subregions. Although in man the HLA-D/DR region cannot at present be subdivided, limited NH2-terminal amino acid sequence data have shown that the DR molecule is homologous to the I-E molecule of the mouse. Furthermore, evidence that DC-1 is not homologous to I-E (and might therefore be homologous to I-A) has been reported. We now report that, using immunoadsorbents prepared with monoclonal antibodies specific for DR or DC-1 antigens, these two human alloantigens were purified from a human lymphoblastoid cell line (LB) and the chains were separated. The NH2-terminal amino acid sequence of the heavy chain of DC-1 antigen shows great structural homology with the murine I-A molecules, thus providing direct evidence of homology of DC-1 to murine I-A.