Role of TRAIL-R in Primary and Secondary Genital and Respiratory Chlamydia muridarum Infections in Mice

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand receptor (TRAIL-R) suppresses inflammation and could therefore affect the course of Chlamydia infections and their long-term sequelae. Wild-type (WT) and TRAIL-R-/- C57BL/6 mice were inoculated vaginally with Chlamydia muridarum; the course of the infection was followed with vaginal cultures and the presence of hydrosalpinx determined. To evaluate the role of TRAIL-R following a secondary infection, the mice were vaginally reinfected. WT and TRAIL-R-/- male mice were also infected and reinfected in the respiratory tract, and the course of the diseases and the infections were followed. Following the primary and secondary vaginal infection, no significant differences in vaginal shedding or hydrosalpinx formation were observed between the WT and TRAIL-R-/- mice. The WT and TRAIL-R-/- mice mounted antibody responses in serum and vaginal washes that were not significantly different. After the primary and secondary intranasal infections of the male mice, changes in body weight were determined, and no significant differences were observed between the WT and TRAIL-R-/- mice. Ten days after the primary and the secondary infections, the weight of the lungs and number of C. muridarum inclusion forming units (IFU) were determined. The lungs of the WT mice weighed less compared with the TRAIL-R-/- mice following a primary infection but not after a secondary infection. No differences in the number of C. muridarum IFU in the lungs were observed between the two groups of mice. In conclusion, despite playing a role in inflammation cell-signaling pathways in vitro, TRAIL-R does not appear to play a major role in the susceptibility, clinical outcomes, or long-term sequelae of C. muridarum infections in vivo. IMPORTANCE TNF-related apoptosis-inducing ligand receptor (TRAIL-R) is involved in suppressing inflammatory responses. Bacterial pathogens such as Chlamydia spp. elicit inflammatory responses in humans following genital, ocular, and respiratory infections. The inflammatory responses are important to control the spread of Chlamydia. However, in certain instances, these inflammatory responses can produce long-term sequelae, including fibrosis. Fibrosis, or scarring, in the genital tract, eye, and respiratory system results in functional deficiencies, including infertility, blindness, and chronic obstructive lung disease, respectively. The goal of this study was to determine if mice deficient in TRAIL-R infected in the genital and respiratory tracts with Chlamydia spp. suffer more or less severe infections, infertility, or lung diseases than wild-type mice. Our results show no differences between the immune responses, infection severity, and long-term sequelae between TRAIL-R knockout and wild-type animals following a genital or a respiratory infection with Chlamydia.

T cell signaling and Treg dysfunction correlate to disease kinetics in IL-2Rα-KO autoimmune mice

IL-2Rα, in part, comprises the high affinity receptor for IL-2, a cytokine important in immune proliferation, activation, and regulation. IL-2Rα deficient mice (IL-2Rα-KO) develop systemic autoimmune disease and die from severe anemia between 18 and 80 days of age. These mice develop kinetically distinct autoimmune progression, with approximately a quarter dying by 21 days of age and half dying after 30 days. This research aims to define immune parameters and cytokine signaling that distinguish cohorts of IL-2Rα-KO mice that develop early- versus late-stage autoimmune disease. To investigate these differences, we evaluated complete blood counts (CBC), antibody binding of RBCs, T cell numbers and activation, hematopoietic progenitor changes, and signaling kinetics, during autoimmune hemolytic anemia (AIHA) and bone marrow failure. We identified several alterations that, when combined, correlate to disease kinetics. Early onset disease correlates with anti-RBC antibodies, lower hematocrit, and reduced IL-7 signaling. CD8 regulatory T cells (Tregs) have enhanced apoptosis in early disease. Further, early and late end stage disease, while largely similar, had several differences suggesting distinct mechanisms drive autoimmune disease kinetics. Therefore, IL-2Rα-KO disease pathology rates, driven by T cell signaling, promote effector T cell activation and expansion and Treg dysfunction.

Immune response against Chlamydia trachomatis via toll-like receptors is negatively regulated by SIGIRR

Chlamydia trachomatis is the most common bacterial sexually-transmitted infection and the major cause of preventable blindness worldwide. The asymptomatic nature of many infections along with uncontrolled inflammation leads to irreversible damage in the upper genital tract and the tarsal conjunctivae, with the major complications of infertility and chronic pelvic pain, and blindness, respectively. Inflammation must, therefore, be tightly regulated to avoid an unrestrained immune response. The genetic factors that regulate inflammation through Toll-like receptor (TLR) signaling pathways during C. trachomatis infection have not been fully characterized. SIGIRR (also known as IL-1R8 or TIR8) can regulate inflammation in response to various pathogens and diseases. However, nothing is known about its role during C. trachomatis infection. Expression of the pro-inflammatory chemokine, IL-8, was measured in epithelial cells infected with C. trachomatis. The effect of SIGIRR was determined by depleting SIGIRR or over-expressing SIGIRR in the epithelial cells before infection. Our results indicate that, in the absence of SIGIRR, epithelial cells induce higher levels of the pro-inflammatory chemokine, IL-8, in response to C. trachomatis infection. In addition, SIGIRR associates with MyD88 in both infected and uninfected infected cells. Collectively, our data demonstrate that SIGIRR functions as a negative regulator of the immune response to C. trachomatis infection. This finding provides insights into the immuno-pathogenesis of C. trachomatis that can be used to treat and identify individuals at risk of uncontrolled inflammation during infection.

CD8 Follicular T Cells Promote B Cell Antibody Class Switch in Autoimmune Disease

CD8 T cells can play both a protective and pathogenic role in inflammation and autoimmune development. Recent studies have highlighted the ability of CD8 T cells to function as T follicular helper (Tfh) cells in the germinal center in the context of infection. However, whether this phenomenon occurs in autoimmunity and contributes to autoimmune pathogenesis is largely unexplored. In this study, we show that CD8 T cells acquire a CD4 Tfh profile in the absence of functional regulatory T cells in both the IL-2-deficient and scurfy mouse models. Depletion of CD8 T cells mitigates autoimmune pathogenesis in IL-2-deficient mice. CD8 T cells express the B cell follicle-localizing chemokine receptor CXCR5, a principal Tfh transcription factor Bcl6, and the Tfh effector cytokine IL-21. CD8 T cells localize to the B cell follicle, express B cell costimulatory proteins, and promote B cell differentiation and Ab isotype class switching. These data reveal a novel contribution of autoreactive CD8 T cells to autoimmune disease, in part, through CD4 follicular-like differentiation and functionality.

Follicular CD8 T cells in autoantibody-mediated disease

The role of CD8 T cells, unlike CD4 T cells, in antibody-mediated autoimmune disease remains largely unexplored. CD8 T cells act both in a cytotoxic CD8 T cell role and helper-like role during autoimmunity. CD4 T follicular cells (Tfh), interact with B cells to promote proliferation, activation and antibody class switching. In autoimmunity, dysregulated self-reactive CD4 Tfh can promote autoantibody production. We have identified a novel population of CD8 T cells within the germinal center that resembles CD4 Tfh cells during systemic autoantibody-mediated disease. IL-2 deficient (IL-2-KO) mice develop systemic autoantibody-mediated disease including autoantibodies against red blood cells (RBC) resulting in autoimmune hemolytic anemia. We show that the absence of either CD4 or CD8 T cells prevents the development of anti-RBC antibodies and reduces lymphoproliferation in IL-2-KO mice. RNA-sequencing of IL-2-KO CD8 T cells revealed an increase in the expression of genes associated with CD4 Tfh lineages (Bcl-6, CXCR5, PD-1, ICOS and IL-21) compared with wild type (WT) CD8 T cells. Flow cytometry of expanded CXCR5+PD-1+ CD4 Tfh cells and CXCR5+PD-1+ CD8 T follicular (Tfc) cells confirms the protein expression of these Tfh markers and the production of IL-21 in IL-2-KO late stage disease (day 18–21). In vitro culture of IL-2-KO CD8 Tfc cells induced antibody class switching in WT B cells at levels similar to that induced by adjuvant-induced WT CD4 Tfh cells. In comparison to CXCR5- PD-1-CD8 T cells, CD8 Tfc cells expressed higher levels of CD40L. Our results indicate that CD8 T cells contribute to autoimmune disease in part through differentiation into follicular T cells that function to induce B cell differentiation and antibody class-switch.

CD8+ T cells drive autoimmune hematopoietic stem cell dysfunction and bone marrow failure

Bone marrow (BM) failure syndrome encompasses a group of disorders characterized by BM stem cell dysfunction, resulting in varying degrees of hypoplasia and blood pancytopenia, and in many patients is autoimmune and inflammatory in nature. The important role of T helper 1 (Th1) polarized CD4⁺ T cells in driving BM failure has been clearly established in several models. However, animal model data demonstrating a functional role for CD8⁺ T cells in BM dysfunction is largely lacking and our objective was to test the hypothesis that CD8⁺ T cells play a non-redundant role in driving BM failure. Clinical evidence implicates a detrimental role for CD8⁺ T cells in BM failure and a beneficial role for Foxp3⁺ regulatory T cells (Tregs) in maintaining immune tolerance in the BM. We demonstrate that IL-2-deficient mice, which have a deficit in functional Tregs, develop spontaneous BM failure. Furthermore, we demonstrate a critical role for CD8⁺ T cells in the development of BM failure, which is dependent on the cytokine, IFNγ. CD8⁺ T cells promote hematopoietic stem cell dysfunction and depletion of myeloid lineage progenitor cells, resulting in anemia. Adoptive transfer experiments demonstrate that CD8⁺ T cells dramatically expedite disease progression and promote CD4⁺ T cell accumulation in the BM. Thus, BM dysregulation in IL-2-deficient mice is mediated by a Th1 and IFNγ-producing CD8⁺ T cell (Tc1) response.

TRAIL-R1 is a negative regulator of pro-inflammatory responses and modulates long-term sequelae resulting from Chlamydia trachomatis infections in humans

The immune system eliminates Chlamydia trachomatis infection through inflammation. However, uncontrolled inflammation can enhance pathology. In mice, TNF-related apoptosis-inducing ligand receptor (TRAIL-R), known for its effects on apoptosis, also regulates inflammation. In humans, the four homologues of TRAIL-R had never been investigated for effects on inflammation. Here, we examined whether TRAIL-R regulates inflammation during chlamydial infection. We examined TRAIL-R1 single nucleotide polymorphisms (SNPs) in an Ecuadorian cohort with and without C. trachomatis infections. There was a highly significant association for the TRAIL+626 homozygous mutant GG for infection vs no infection in this population. To confirm the results observed in the human population, primary lung fibroblasts and bone marrow-derived macrophages (BMDMs) were isolated from wildtype (WT) and TRAIL-R-deficient mice, and TRAIL-R1 levels in human cervical epithelial cells were depleted by RNA interference. Infection of BMDMs and primary lung fibroblasts with C. trachomatis strain L₂, or the murine pathogen C. muridarum, led to higher levels of MIP2 mRNA expression or IL-1β secretion from TRAIL-R-deficient cells than WT cells. Similarly, depletion of TRAIL-R1 expression in human epithelial cells resulted in a higher level of IL-8 mRNA expression and protein secretion during C. trachomatis infection. We conclude that human TRAIL-R1 SNPs and murine TRAIL-R modulate the innate immune response against chlamydial infection. This is the first evidence that human TRAIL-R1 is a negative regulator of inflammation and plays a role in modulating Chlamydia pathogenesis.

Transcription factor complex AP-1 mediates inflammation initiated by Chlamydia pneumoniae infection

Chlamydia pneumoniae is responsible for a high prevalence of respiratory infections worldwide and has been implicated in atherosclerosis. Inflammation is regulated by transcription factor (TF) networks. Yet, the core TF network triggered by chlamydiae remains largely unknown. Primary human coronary artery endothelial cells were mock-infected or infected with C. pneumoniae to generate human transcriptome data throughout the chlamydial developmental cycle. Using systems network analysis, the predominant TF network involved receptor, binding and adhesion and immune response complexes. Cells transfected with interfering RNA against activator protein-1 (AP-1) members FOS, FOSB, JUN and JUNB had significantly decreased expression and protein levels of inflammatory mediators interleukin (IL)6, IL8, CD38 and tumour necrosis factor compared with controls. These mediators have been shown to be associated with C. pneumoniae disease. Expression of AP-1 components was regulated by MAPK3K8, a MAPK pathway component. Additionally, knock-down of JUN and FOS showed significantly decreased expression of Toll-like receptor (TLR)3 during infection, implicating JUN and FOS in TLR3 regulation. TLR3 stimulation led to elevated IL8. These findings suggest that C. pneumoniae initiates signalling via TLR3 and MAPK that activate AP-1, a known immune activator in other bacteria not previously shown for chlamydiae, triggering inflammation linked to C. pneumoniae disease.

Single-cell analysis of murine long-term hematopoietic stem cells reveals distinct patterns of gene expression during fetal migration

BACKGROUND

Long-term hematopoietic stem cells (LT-HSCs) migrate from the fetal liver (FL) to the fetal bone marrow (FBM) during development. Various adhesion and chemotactic receptor genes have been implicated in the migration of adult LT-HSCs. However, their role in the migration of fetal LT-HSCs is not clearly understood due, in part, to the rare number of these cells in fetal tissues, which preclude classical gene expression analysis. The aim of this study is to characterize the expression of migration related genes in fetal LT-HSC across different anatomical locations during development.

METHODOLOGY/PRINCIPAL FINDINGS

We isolated fetal LT-HSC from different developmental stages, as well as different anatomical locations, and performed single-cell multiplex RT-qPCR and flow cytometry analysis of eight molecules involved in adult LT-HSC migration. Our results show that the gene expression of the chemokine receptor Cxcr4 in LT-HSC varies across developmental microenvironments and times, while the cadherin Cdh2 (Ncad) and the calcium receptor Casr show higher gene expression and variability only in FBM at 17.5 days post coitum (dpc). The cadherin Cdh5 (Vecad) maintains high expression variability only during fetal development, while the integrin subunit Itga5 (α5) increases its variability after 14.5 dpc. The integrin subunits Itga4 (α4) and Itgal (Lfa1), as well as the selectin ligand Selplg (Psgl1), did not show differences in their expression in single LT-HSCs irrespective of the developmental times or anatomical microenvironments studied.

CONCLUSIONS/SIGNIFICANCE

Our data demonstrate that the expression pattern of phenotypically identical, single LT-HSCs fluctuates as a function of developmental stage and anatomical microenvironment. This is the first exhaustive gene expression comparison of migration-related molecules in fetal tissues across developmental times, enhancing the understanding of LT-HSC migration fate decisions during development.

Single-cell multiplex RT-qPCR analysis of genes related to migration of murine long-term hematopoietic stem cells during development (65.48)

Hematopoietic stem cells (HSC) follow a defined pattern of migration in development. By E14.5, HSC are found in the fetal liver (FL) and colonize the fetal bone marrow (FBM) by E17.5, where they remain during adult life. The mechanism governing HSC migration from the FL to the FBM is not clearly understood. We performed single-cell multiplex RT-qPCR and FACS analysis of 8 genes involved in HSC migration. We show that the expression of the chemokine receptor Cxcr4 varies across microenvironments and developmental times, while N-cadherin and the calcium receptor Casr show only gene expression in FBM at E17.5. Moreover, VE-cadherin maintains high expression only during fetal development, while the integrin subunit α5 increases its variability after E14.5. The integrin subunits α4 and αL as well as the selectin ligand Psgl1 did not show differences in their expression in single HSCs irrespective of the microenvironment. Our data demonstrate that the expression pattern of phenotypically identical, single HSCs fluctuates as a function of developmental and anatomical microenvironment, an observation that could be overlooked using whole population gene expression analysis. This is the first gene expression comparison of migration-related molecules in fetal tissues across developmental times, enhancing the understanding of HSC migration during development. These findings may have potential relevance in improving BM engraftment of clinically transplanted HSC.

Age related dynamics of committed T cell progenitors in mice (36.57)

Immunosenescence is the reduced ability of the body to mediate an adaptive immune response. Multiple factors contribute to immunosenescence, including age-related changes in hematopoietic stem cell (HSC) phenotype, its niche, and the tissues responsible for lymphocyte development, such as the bone marrow and the thymus. Therefore, understanding lymphocyte development in the aged is fundamental to enhance the immune response capacity of the aging immune system. Here, we investigate the age-related dynamics of committed T cell progenitors (CTP), an HSC-derived bone marrow population capable of generating functional T cells via both thymic and extrathymic pathways. Specifically, we examined the CTP’s frequency and absolute numbers in the bone marrow of young (1 month) and old (12 and 18 months) C57BL/6 mice using flow cytometry. Moreover, we compared the capability of young and aged CTP to generate T cells in vitro. Understanding the biology of CTP in relationship to aging could have important clinical applications in the treatment of diseases related to immunodeficiencies and cancer by hematopoietic stem cell transplantation, as CTP-derived T cells protect against viral infections without inducing graft vs. host disease. This work could pave the way to studies related to human CTP populations and their therapeutic potential.

Analysis of signals that regulate the fate of early T cell precursors (36.53)

The differentiation process of Hematopoietic Stem Cells (HSC) to Common Lymphoid Progenitors (CLP), that give raise to dendritic, NK, B and T cells, depends on various cues received from their microenvironment. Notch-1 is a transmembrane receptor that plays a crucial role on CLP commitment towards T cell lineage at the expense of B cell fate. The role of the transcription factor GATA-3, as well as its regulatory interaction with Notch-1 signals during early T cell development, is poorly characterized. In vitro studies show that GATA-3-deficient (GATA-3-/-) T cell progenitors do not develop beyond the CD44+CD25+ double negative 2 (DN2) stage. Remarkably, GATA-3-/- DN2 cells generate B cells in the presence of constant Notch-1 signals, which normally block B cell development. These GATA-3-/- DN2 cell express elevated levels of Deltex-1, a Notch-1 regulator. Therefore, we hypothesize that GATA-3 transcriptional activity controls the expression of Deltex-1 and possibly other Notch-1 regulators. The expression levels of various regulators of Notch-1 in wild type and GATA-3-/- T cell progenitors will be evaluated using quantitative PCR. The effect of GATA-3 deficiency on the expression level of various genes involved in Notch signaling will be evaluated by qPCR array. Revealing the interaction mechanism of GATA-3 with Notch-1 will contribute to our understanding of how early lymphocyte progenitors become committed toward the T cell lineage.

Discovery of novel epigenetic markers in non-Hodgkin's lymphoma

Non-Hodgkin's lymphoma (NHL) is a group of malignancies with heterogeneous genetic and epigenetic alterations. Discovery of molecular markers that better define NHL should improve diagnosis, prognosis and understanding of the biology. We developed a CpG island DNA microarray for discovery of aberrant methylation targets in cancer, and now apply this method to examine NHL cell lines and primary tumors. This methylation profiling revealed differential patterns in six cell lines originating from different subtypes of NHL. We identified 30 hypermethylated genes in these cell lines and independently confirmed 10 of them. Methylation of 6 of these genes was then further examined in 75 primary NHL specimens composed of four subtypes representing different stages of maturation. Each gene (DLC-1, PCDHGB7, CYP27B1, EFNA5, CCND1 and RARbeta2) was frequently hypermethylated in these NHLs (87, 78, 61, 53, 40 and 38%, respectively), but not in benign follicular hyperplasia. Although some genes such as DLC-1 and PCDHGB7 were methylated in the vast majority of NHLs, others were differentially methylated in specific subtypes. The methylation of the candidate tumor suppressor gene DLC-1 was detected in a high proportion of primary tumor and plasma DNA samples by using quantitative methylation-specific PCR analysis. This promoter hypermethylation inversely correlated with DLC-1 gene expression in primary NHL samples. Thus, this CpG island microarray is a powerful discovery tool to identify novel methylated genes for further studies of their relevant molecular pathways in NHLs and identification of potential epigenetic biomarkers of disease.