CD69 limits early inflammatory diseases associated with immune response to Listeria monocytogenes infection

HDAC6 Deletion Decreases Pristane-induced Inflammation

Systemic lupus erythematosus is an autoimmune disease characterized by excessive inflammation and production of pathogenic Abs. Histone deacetylase 6 (HDAC6) is a class IIb histone deacetylase. It has been reported that selective HDAC6 inhibition decreases inflammation in lupus mouse models. In this study, sex- and age-matched wild-type (WT) and HDAC6-/- mice on the C57BL/6 background were administered 0.5 ml of pristane or PBS i.p. at 8-12 wk of age and were euthanized 10 d later. At sacrifice, body weight and spleen weight were measured, sera were collected, and splenocytes and peritoneal cells were harvested for flow cytometry. We found pristane administration increased the spleen weight with no difference between WT and HDAC6-/- mice. Pristane administration promoted the population of CD11b+Ly6C++ inflammatory monocytes and CD11b+Ly6G+ neutrophils. Peritoneal recruitment of these inflammatory monocytes and neutrophils was significantly decreased in HDAC6-/- mice compared with the WT mice. Flow cytometry results showed that the number of CD69+ T and B cells was increased in HDAC6-/- mice. Pristane administration also induced the IFN signature genes as determined by RT-qPCR. Furthermore, IFN signature genes were not affected in HDAC6-/- mice compared with the WT mice. In vitro studies in J774A.1 cells revealed that the selective HDAC6 inhibitor (ACY-738) increased acetylation of NF-κB while increasing Stat1 phosphorylation, which resulted in inducible NO synthase production in LPS/IFN-γ-stimulated cells. Taken together, these results demonstrate that although HDAC6 inhibition may inhibit some inflammatory pathways, others remain unaffected.

Enhanced SARS-CoV-2-Specific CD4+ T Cell Activation and Multifunctionality in Late Convalescent COVID-19 Individuals

Background: Examination of CD4+ T cell responses during the natural course of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection offers useful information for the improvement of vaccination strategies against this virus and the protective effect of these T cells. Methods: We characterized the SARS-CoV-2-specific CD4+ T cell activation marker, multifunctional cytokine and cytotoxic marker expression in recovered coronavirus disease 2019 (COVID-19) individuals. Results: CD4+ T-cell responses in late convalescent (>6 months of diagnosis) individuals are characterized by elevated frequencies of activated as well as mono, dual- and multi-functional Th1 and Th17 CD4+ T cells in comparison to early convalescent (<1 month of diagnosis) individuals following stimulation with SARS-CoV-2-specific antigens. Similarly, the frequencies of cytotoxic marker expressing CD4+ T cells were also enhanced in late convalescent compared to early convalescent individuals. Conclusion: Our findings from a low-to middle-income country suggest protective adaptive immune responses following natural infection of SARS-CoV-2 are elevated even at six months following initial symptoms, indicating the CD4+ T cell mediated immune protection lasts for six months or more in natural infection.

[Significance of evaluation of CD69 expression by peripheral blood lymphocytes for predicting pregnancy outcome in women with recurrent pregnancy loss]

The aim of this work was to characterize phenotypically peripheral blood T- and NK lymphocytes expressing an early marker of activation, CD69, and assess the significance of CD69 expression for predicting pregnancy outcome in women with idiopathic reccurent pregnancy loss (IRP) before and after immunocytotherapy (ICT). The study group consisted of 36 patients with IRP who became pregnant after pre-gestational allimmunization, in 30 patients the pregnancy was prolonged to the full term and ended with the birth of a viable baby, in 6 - it was terminated before 12 weeks of gestation. In the control group, 15 fertile women outside pregnancy and 11 women at 12 weeks of physiological pregnancy were examined. Assessment of the CD69 expression in women with prolonged pregnancy revealed the absence of significant differences with the control group in the content and proportion of activated lymphocytes (CD69+). In women with aborted pregnancy after pre-gestational ICT, an increase in the number of almost all analyzed lymphocyte subpopulations responding to the activation stimulus, with a clear tendency to increase the proportion of activated T- but not NK-lymphocytes was found. At 5-6 weeks, the proportion of activated lymphocytes among a subpopulation of cytotoxic T-lymphocytes (CD3+CD8+/CD3+CD8+CD69+) in these women was significantly higher than in women with prolonged pregnancy, which confirms the leading role of effector cytotoxic T-lymphocytes in rejection reactions. Thus, the studies showed the promise of evaluating the expression of the early activation marker CD69 as an additional laboratory criterion for the personable appointment of immunocytotherapy to women with a common reccurent pregnancy loss.

Functional Characterization of a Dual Enhancer/Promoter Regulatory Element Leading Human CD69 Expression

The CD69 gene encodes a C-type lectin glycoprotein with immune regulatory properties which is expressed on the cell surfaces of all activated hematopoietic cells. CD69 activation kinetics differ by developmental stage, cell linage and activating conditions, and these differences have been attributed to the participation of complex gene regulatory networks. An evolutionarily conserved regulatory element, CNS2, located 4kb upstream of the CD69 gene transcriptional start site, has been proposed as the major candidate governing the gene transcriptional activation program. To investigate the function of human CNS2, we studied the effect of its endogenous elimination via CRISPR-Cas9 on CD69 protein and mRNA expression levels in various immune cell lines. Even when the entire promoter region was maintained, CNS2-/- cells did not express CD69, thus indicating that CNS2 has promoter-like characteristics. However, like enhancers, inverted CNS2 sustained transcription, although at a diminished levels, thereby suggesting that it has dual promoter and enhancer functions. Episomal luciferase assays further suggested that both functions are combined within the CNS2 regulatory element. In addition, CNS2 directs its own bidirectional transcription into two different enhancer-derived RNAs molecules (eRNAs) which are transcribed from two independent transcriptional start sites in opposite directions. This eRNA transcription is dependent on only the enhancer sequence itself, because in the absence of the CD69 promoter, sufficient RNA polymerase II levels are maintained at CNS2 to drive eRNA expression. Here, we describe a regulatory element with overlapping promoter and enhancer functions, which is essential for CD69 gene transcriptional regulation.

Decreased Expression of CD69 on T Cells in Tuberculosis Infection Resisters

BACKGROUND

CD69 is a biomarker of T-cell activation status, but its activation status in human Mycobacterium tuberculosis (Mtb) infection remains elusive.

METHODS

A set of cohorts of patients with different tuberculosis (TB) infection status including active TB patients (ATB), latent tuberculous infection patients (LTBI) and close contacts (CCs) of ATB was designed, and the expression profiles of CD69 and several T-cell markers were determined on Mtb antigen-stimulated T cells by flow cytometry.

RESULTS

The frequencies of CD4+ and CD8+ T cells were both comparable among Mtb-infected individuals including ATB and LTBI, which guaranteed the consistency of the background level. A t-Distributed Stochastic Neighbor Embedding (tSNE) analysis on a panel of six phenotypic markers showed a unique color map axis gated on T cells in the CCs group compared with ATB and LTBI populations. By further gating on cells positive for each individual marker and then overlaying those events on top of the tSNE plots, their distribution suggested that some markers were expressed differently in the CCs group. Further analysis showed that the expression levels of CD69 on both CD4+ and CD8+ T cells were significantly lower in the CCs group, especially in interferon-γ-responding T cells.

CONCLUSION

Our findings suggest that the T-cell activation status of CD69 is associated with Mtb infection and may have the potential to distinguish LTBI from those populations who have been exposed continuously to Mtb but have not become infected.

CD69 Targeting Enhances Anti-vaccinia Virus Immunity

CD69 is highly expressed on the leukocyte surface upon viral infection, and its regulatory role in the vaccinia virus (VACV) immune response has been recently demonstrated using CD69^-/- mice. Here, we show augmented control of VACV infection using the anti-human CD69 monoclonal antibody (MAb) 2.8 as both preventive and therapeutic treatment for mice expressing human CD69. This control was related to increased natural killer (NK) cell reactivity and increased numbers of cytokine-producing T and NK cells in the periphery. Moreover, similarly increased immunity and protection against VACV were reproduced over both long and short periods in anti-mouse CD69 MAb 2.2-treated immunocompetent wild-type (WT) mice and immunodeficient Rag2^-/- CD69^+/+ mice. This result was not due to synergy between infection and anti-CD69 treatment since, in the absence of infection, anti-human CD69 targeting induced immune activation, which was characterized by mobilization, proliferation, and enhanced survival of immune cells as well as marked production of several innate proinflammatory cytokines by immune cells. Additionally, we showed that the rapid leukocyte effect induced by anti-CD69 MAb treatment was dependent on mTOR signaling. These properties suggest the potential of CD69-targeted therapy as an antiviral adjuvant to prevent derived infections.IMPORTANCE In this study, we demonstrate the influence of human and mouse anti-CD69 therapies on the immune response to VACV infection. We report that targeting CD69 increases the leukocyte numbers in the secondary lymphoid organs during infection and improves the capacity to clear the viral infection. Targeting CD69 increases the numbers of gamma interferon (IFN-γ)- and tumor necrosis factor alpha (TNF-α)-producing NK and T cells. In mice expressing human CD69, treatment with an anti-CD69 MAb produces increases in cytokine production, survival, and proliferation mediated in part by mTOR signaling. These results, together with the fact that we have mainly worked with a human-CD69 transgenic model, reveal CD69 as a treatment target to enhance vaccine protectiveness.

Identification of the association between rs41274221 polymorphism in the seed sequence of microRNA-25 and the risk of neonate sepsis

BACKGROUND

Many studies have investigated the role of microRNA-25 (miR-25) in the initiation and progression of sepsis in newborns. In this study, we aim to explore how rs41274221 polymorphism in miR-25 compromises the interaction between miR-25 and CD69, so as to understand the mechanisms involved in the control of sepsis in newborns.

METHODS

Computational analysis, luciferase assay, real-time polymerase chain reaction (PCR), and western blot analysis were performed in this study.

RESULTS

The luciferase assays results showed that CD69 was a target gene of miR-25, because the luciferase activity in cells transfected with wild type CD69 was much lower than that in the cells transfected with mutant CD69 or the scramble control. Real-time PCR and western blot analysis results showed that the expression of miR-25 in sepsis patients was significantly upregulated as compared with that in the normal control group, and the CD69 position ratio as well as the messenger RNA (mRNA) and protein level of CD69 in sepsis patients was much higher than those in the normal control group. As compared with the scramble control, miR-25 mimics, and CD69 small interfering RNA (siRNA) downregulated the mRNA and protein expression of CD69, whereas the expression of CD69 mRNA and protein in cells transfected with miR-25 inhibitors was significantly higher as compared with that in the scramble control. In addition, interferonγ production was significantly downregulated in cells transfected with miR-25 inhibitors but notably upregulated in cells transfected with miR-25 mimics or CD69 siRNA.

CONCLUSION

The single-nucleotide polymorphism (SNP; rs41274221) in miR-25 is associated with the risk of sepsis in newborns.

The Conserved Non-Coding Sequence 2 (CNS2) Enhances CD69 Transcription through Cooperation between the Transcription Factors Oct1 and RUNX1

The immune regulatory receptor CD69 is expressed upon activation in all types of leukocytes and is strongly regulated at the transcriptional level. We previously described that, in addition to the CD69 promoter, there are four conserved noncoding regions (CNS1-4) upstream of the CD69 promoter. Furthermore, we proposed that CNS2 is the main enhancer of CD69 transcription. In the present study, we mapped the transcription factor (TF) binding sites (TFBS) from ChIP-seq databases within CNS2. Through luciferase reporter assays, we defined a ~60 bp sequence that acts as the minimum enhancer core of mouse CNS2, which includes the Oct1 TFBS. This enhancer core establishes cooperative interactions with the 3′ and 5′ flanking regions, which contain RUNX1 BS. In agreement with the luciferase reporter data, the inhibition of RUNX1 and Oct1 TF expression by siRNA suggests that they synergistically enhance endogenous CD69 gene transcription. In summary, we describe an enhancer core containing RUNX1 and Oct1 BS that is important for the activity of the most potent CD69 gene transcription enhancer.

The Functional Requirement for CD69 in Establishment of Resident Memory CD8+ T Cells Varies with Tissue Location

Recent studies have characterized populations of memory CD8⁺ T cells that do not recirculate through the blood but are, instead, retained in nonlymphoid tissues. Such CD8⁺ tissue resident memory T cells (T_RM) are critical for pathogen control at barrier sites. Identifying T_RM and defining the basis for their tissue residency is therefore of considerable importance for understanding protective immunity and improved vaccine design. Expression of the molecule CD69 is widely used as a definitive marker for T_RM, yet it is unclear whether CD69 is universally required for producing or retaining T_RM Using multiple mouse models of acute immunization, we found that the functional requirement for CD69 was highly variable, depending on the tissue examined, playing no detectable role in generation of T_RM at some sites (such as the small intestine), whereas CD69 was critical for establishing resident cells in the kidney. Likewise, forced expression of CD69 (but not expression of a CD69 mutant unable to bind the egress factor S1PR1) promoted CD8⁺ T_RM generation in the kidney but not in other tissues. Our findings indicate that the functional relevance of CD69 in generation and maintenance of CD8⁺ T_RM varies considerably, chiefly dependent on the specific nonlymphoid tissue studied. Together with previous reports that suggest uncoupling of CD69 expression and tissue residency, these findings prompt caution in reliance on CD69 expression as a consistent marker of CD8⁺ T_RM.

Crucial role for CD69 in allergic inflammatory responses: CD69-Myl9 system in the pathogenesis of airway inflammation

CD69 has been known as an early activation marker of lymphocytes; whereas, recent studies demonstrate that CD69 also has critical functions in immune responses. Early studies using human samples revealed the involvement of CD69 in various inflammatory diseases including asthma. Moreover, murine disease models using Cd69^-/- mice and/or anti-CD69 antibody (Ab) treatment have revealed crucial roles for CD69 in inflammatory responses. However, it had not been clear how the CD69 molecule contributes to the pathogenesis of inflammatory diseases. We recently elucidated a novel mechanism, in which the interaction between CD69 and its ligands, myosin light chain 9, 12a and 12b (Myl9/12) play a critical role in the recruitment of activated T cells into the inflammatory lung. In this review, we first summarize CD69 function based on its structure and then introduce the evidence for the involvement of CD69 in human diseases and murine disease models. Then, we will describe how we discovered CD69 ligands, Myl9 and Myl12, and how the CD69-Myl9 system regulates airway inflammation. Finally, we will discuss possible therapeutic usages of the blocking Ab to the CD69-Myl9 system.

Treatment of HIV-Infected Individuals with the Histone Deacetylase Inhibitor Panobinostat Results in Increased Numbers of Regulatory T Cells and Limits Ex Vivo Lipopolysaccharide-Induced Inflammatory Responses

The effect of treatment with histone deacetylase inhibitors on the immune system in HIV-infected individuals is not clear. Analysis of results from a clinical trial in which 15 HIV-infected individuals received 12 doses of panobinostat identified a significant impact on both T cell activation status and regulatory T cell suppressive marker expression and a reduced level of monocytic responsiveness to inflammatory stimuli. These changes were substantiated by global gene expression analysis. Collectively, the results suggest that panobinostat has multiple effects on innate and adaptive immune responses. Importantly, all the effects were transient, and further panobinostat treatment did not cause persistent long-term changes in gene expression patterns in HIV-infected individuals.

Histone deacetylase inhibitors (HDACi) modulate the transcriptional activity of all cells, including innate and adaptive immune cells. Therefore, we aimed to evaluate immunological effects of treatment with the HDACi panobinostat in HIV-infected patients during a clinical phase IIa latency reversal trial. Using flow cytometry, we investigated changes in T cell activation (CD69, CD38, HLA-DR) and the expression of CD39 and CTLA4 on regulatory T cells (Tregs). Whole-blood stimulations were performed and cytokine responses measured using Luminex. Gene expression in purified peripheral blood mononuclear cells (PBMCs) was evaluated using an Affymetrix HTA 2.0 gene chip. We found that proportions of CD4⁺ and CD8⁺ T cells expressing CD69 increased 24 h after initial panobinostat administration (P < 0.01), followed by an increase in the proportions of CD38⁺ HLA-DR⁺-coexpressing CD4⁺ T cells on day 4 (P = 0.02). Concurrently, proportions of Tregs increased by 40% (P = 0.003). Treg CTLA4 median fluorescent intensity (MFI) increased by 25% (P = 0.007), and CD39 MFI on CD39⁺ Treg increased by 12% (P = 0.02). Lipopolysaccharide (LPS)-induced inflammatory responses (interleukin-1β [IL-1β], IL-6, IL-12p40, and tumor necrosis factor alpha [TNF-α]) in whole blood were significantly downregulated 4 days after initial dosing. Lastly, panobinostat induced significant changes in the overall gene expression pattern (fold change, >1.5; false-discovery-rate [FDR]-corrected P, <0.05). Importantly, measures of immune function returned to baseline after panobinostat treatment and follow-up revealed no sustained effect on overall gene expression.

IMPORTANCE The effect of treatment with histone deacetylase inhibitors on the immune system in HIV-infected individuals is not clear. Analysis of results from a clinical trial in which 15 HIV-infected individuals received 12 doses of panobinostat identified a significant impact on both T cell activation status and regulatory T cell suppressive marker expression and a reduced level of monocytic responsiveness to inflammatory stimuli. These changes were substantiated by global gene expression analysis. Collectively, the results suggest that panobinostat has multiple effects on innate and adaptive immune responses. Importantly, all the effects were transient, and further panobinostat treatment did not cause persistent long-term changes in gene expression patterns in HIV-infected individuals.

IRF6 Regulates Alternative Activation by Suppressing PPARγ in Male Murine Macrophages

Aberrant proinflammatory and suppressed anti-inflammatory (alternative; M2) macrophage activation underlies the chronic inflammation associated with obesity and other metabolic disorders. This study demonstrates a critical role for interferon regulatory factor 6 (IRF6) in regulating macrophage M2 activation by suppressing peroxisome proliferator-activated receptor-γ (PPARγ) expression, a critical regulator of alternative macrophage polarization. The data demonstrate suppression of IRF6 in both M2 macrophages and obese adipose tissue macrophages. Using gain- and loss-of-function strategies, we confirmed that IRF6 knockdown enhanced M2 activation, whereas IRF6 overexpression dramatically attenuated M2 activation. Computational target prediction analysis coupled with chromatin immunoprecipitation indicated that IRF6 suppresses PPARγ through binding IRF recognition sites located upstream of the PPARγ coding region. Taken together, our results suggest that an IRF6/PPARγ regulatory axis suppresses anti-inflammatory responses in bone marrow-derived macrophages and provides references for future study addressing dysregulated metabolic and immunologic homeostasis of obese adipose tissue.

CD69: from activation marker to metabolic gatekeeper

CD69 is a membrane-bound, type II C-lectin receptor. It is a classical early marker of lymphocyte activation due to its rapid appearance on the surface of the plasma membrane after stimulation. CD69 is expressed by several subsets of tissue resident immune cells, including resident memory T (TRM) cells and gamma delta (γδ) T cells, and is therefore considered a marker of tissue retention. Recent evidence has revealed that CD69 regulates some specific functions of selected T-cell subsets, determining the migration-retention ratio as well as the acquisition of effector or regulatory phenotypes. Specifically, CD69 regulates the differentiation of regulatory T (Treg) cells as well as the secretion of IFN-γ, IL-17, and IL-22. The identification of putative CD69 ligands, such as Galectin-1 (Gal-1), suggests that CD69-induced signaling can be regulated not only during cognate contacts between T cells and antigen-presenting cells in lymphoid organs, but also in the periphery, where cytokines and other metabolites control the final outcome of the immune response. Here, we will discuss new aspects of the molecular signaling mediated by CD69 and its involvement in the metabolic reprogramming regulating TH-effector lineages.

The Protective Role of Type I Interferons in the Gastrointestinal Tract

The immune system of the gastrointestinal (GI) tract manages the significant task of recognizing and eliminating pathogens while maintaining tolerance of commensal bacteria. Dysregulation of this delicate balance can be detrimental, resulting in severe inflammation, intestinal injury, and cancer. Therefore, mechanisms to relay important signals regulating cell growth and immune reactivity must be in place to support GI homeostasis. Type I interferons (IFN-I) are a family of pleiotropic cytokines, which exert a wide range of biological effects including promotion of both pro- and anti-inflammatory activities. Using animal models of colitis, investigations into the regulation of intestinal epithelium inflammation highlight the role of IFN-I signaling during fine modulation of the immune system. The intestinal epithelium of the gut guides the immune system to differentiate between commensal and pathogenic microbiota, which relies on intimate links with the IFN-I signal-transduction pathway. The current paradigm depicts an IFN-I-induced antiproliferative state in the intestinal epithelium enabling cell differentiation, cell maturation, and proper intestinal barrier function, strongly supporting its role in maintaining baseline immune activity and clearance of damaged epithelia or pathogens. In this review, we will highlight the importance of IFN-I in intestinal homeostasis by discussing its function in inflammation, immunity, and cancer.

Comparative Analysis of Conventional Natural Killer Cell Responses to Acute Infection with Toxoplasma gondii Strains of Different Virulence

Conventional natural killer (cNK) cells, members of group 1 innate lymphoid cells, are a diverse cell subpopulation based on surface receptor expression, maturation, and functional potential. cNK cells are critical for early immunity to Toxoplasma gondii via IFNγ production. Acute cNK cell responses to infection with different strains of T. gondii have not yet been characterized in detail. Here, we comprehensively performed this analysis with Type I virulent RH, Type II avirulent ME49, and fully attenuated Type I cps1-1 strains. In response to these three parasite strains, murine cNK cells produce IFNγ and become cytotoxic and polyfunctional (IFNγ+CD107a+) at the site of infection. In contrast to virulent RH and avirulent ME49 T. gondii strains, attenuated cps1-1 induced only local cNK cell responses. Infections with RH and ME49 parasites significantly decreased cNK cell frequency and numbers in spleen 5 days post infection compared with cps1-1 parasites. cNK cell subsets expressing activating receptors Ly49H, Ly49D, and NKG2D and inhibitory receptors Ly49I and CD94/NKG2A were similar when compared between the strains and at 5 days post infection. cNK cells were not proliferating (Ki67−) 5 days post infection with any of the strains. cNK cell maturation as measured by CD27, CD11b, and KLRG1 was affected after infection with different parasite strains. RH and ME49 infection significantly reduced mature cNK cell frequency and increased immature cNK cell populations compared with cps1-1 infection. Interestingly, KLRG1 was highly expressed on immature cNK cells after RH infection. After RH and ME49 infections, CD69+ cNK cells in spleen were present at higher frequency than after cps1-1 infection, which may correlate with loss of the mature cNK cell population. Cytokine multiplex analysis indicated cNK cell responses correlated with peritoneal exudate cell, spleen, and serum proinflammatory cytokine levels, including IL-12. qPCR analysis of parasite-specific B1 gene revealed that parasite burdens may affect cNK cell responses. This study demonstrates infection with RH and ME49 parasites impacts cNK cell maturation during acute T. gondii infection. Different cNK cell responses could impact early immunity and susceptibility to these strains.

CD69 Deficiency Enhances the Host Response to Vaccinia Virus Infection through Altered NK Cell Homeostasis

During the host response to viral infection, the transmembrane CD69 protein is highly upregulated in all immune cells. We have studied the role of CD69 in the murine immune response to vaccinia virus (VACV) infection, and we report that the absence of CD69 enhances protection against VACV at both short and long times postinfection in immunocompetent and immunodeficient mice. Natural killer (NK) cells were implicated in the increased infection control, since the differences were greatly diminished when NK cells were depleted. This role of NK cells was not based on an altered NK cell reactivity, since CD69 did not affect the NK cell activation threshold in response to major histocompatibility complex class I NK cell targets or protein kinase C activation. Instead, NK cell numbers were increased in the spleen and peritoneum of CD69-deficient infected mice. That was not just secondary to better infection control in CD69-deficient mice, since NK cell numbers in the spleens and the blood of uninfected CD69(-/-) mice were already augmented. CD69-deficient NK cells from infected mice did not have an altered proliferation capacity. However, a lower spontaneous cell death rate was observed for CD69(-/-) lymphocytes. Thus, our results suggest that CD69 limits the innate immune response to VACV infection at least in part through cell homeostatic survival.

IMPORTANCE

We show that increased natural killer (NK) cell numbers augment the host response and survival after infection with vaccinia virus. This phenotype is found in the absence of CD69 in immunocompetent and immunodeficient hosts. As part of the innate immune system, NK lymphocytes are activated and participate in the defense against infection. Several studies have focused on the contribution of NK cells to protection against infection with vaccinia virus. In this study, it was demonstrated that the augmented early NK cell response in the absence of CD69 is responsible for the increased protection seen during infection with vaccinia virus even at late times of infection. This work indicates that the CD69 molecule may be a target of therapy to augment the response to poxvirus infection.

Anti-CD69 monoclonal antibody treatment inhibits airway inflammation in a mouse model of asthma

OBJECTIVE

Airway inflammation and airway hyper-responsiveness (AHR) are principle pathological manifestations of asthma. Cluster of differentiation 69 (CD69) is a well-known co-stimulatory factor associated with the activation, proliferation as well as apoptosis of immune cells. This study aims to examine the effect of anti-CD69 monoclonal antibody (mAb) on the pathophysiology of a mouse model of asthma.

METHODS

A murine model of ovalbumin (OVA)-induced allergic airway inflammation was used in this study. Briefly, mice were injected with 20 μg chicken OVA intraperitoneally on Days 0 and 14, followed by aerosol provocation with 1% (0.01 g/ml) OVA on Days 24, 25, and 26. Anti-CD69 mAb or isotype IgG was injected intraperitoneally after OVA challenge; dexamethasone (DXM) was administrated either before or after OVA challenge. AHR, mucus production, and eosinophil infiltration in the peribronchial area were examined. The levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-5 (IL-5) in bronchoalveolar lavage fluid (BALF) were also assayed as indices of airway inflammation on Day 28 following OVA injection.

RESULTS

Pretreatment with DXM together with anti-CD69 mAb treatment after OVA provocation completely inhibited AHR, eosinophil infiltration and mucus overproduction, and significantly reduced BALF IL-5. However, treatment with DXM alone after OVA challenge only partially inhibited AHR, eosinophil infiltration and mucus overproduction, and did not diminish BALF IL-5. Treatment with either DXM or anti-CD69 mAb did not alter the concentration of BALF GM-CSF.

CONCLUSIONS

Anti-CD69 mAb treatment inhibits established airway inflammation as effectively as DXM pretreatment. This study provides a potential alternative therapeutic opportunity for the clinical management of asthma and its exacerbation.

Group B Streptococcus Induces a Robust IFN-γ Response by CD4(+) T Cells in an In Vitro and In Vivo Model

Group B Streptococcus (GBS) serotype III causes life-threatening infections. Cytokines have emerged as important players for the control of disease, particularly IFN-γ. Although potential sources of this cytokine have been proposed, no specific cell line has ever been described as a leading contributor. In this study, CD4⁺ T cell activation profiles in response to GBS were evaluated through in vivo, ex vivo, and in vitro approaches. Total splenocytes readily produce a type 1 proinflammatory response by releasing IFN-γ, TNF-α, and IL-6 and actively recruit T cells via chemokines like CXCL9, CXCL10, and CCL3. Responding CD4⁺ T cells differentiate into Th1 cells producing large amounts of IFN-γ, TNF-α, and IL-2. In vitro studies using dendritic cell and CD4⁺ T cell cocultures infected with wild-type GBS or a nonencapsulated mutant suggested that GBS capsular polysaccharide, one of the major bacterial virulence factors, differentially modulates surface expression of CD69 and IFN-γ production. Overall, CD4⁺ T cells are important producers of IFN-γ and might thus influence the course of GBS infection through the expression balance of this cytokine.

Glycosylation-dependent interaction between CD69 and S100A8/S100A9 complex is required for regulatory T-cell differentiation

Cluster of differentiation (CD)69 is a leukocyte activation receptor involved in the maintenance of immune homeostasis and is positively selected in activated regulatory T (Treg) cells, implicating its role during Treg-cell differentiation. By RNA interference, we show that CD69 is not sufficient to support the conversion of CD4(+) naive T cells into Treg cells, whereas it does that of human peripheral blood mononuclear cells (hPBMCs) (P < 0.01), suggesting that a ligand-receptor interaction is required for CD69 function. Using immunoprecipitation and mass spectrometry, we identified the S100A8/S100A9 complex as the natural ligand of CD69 in hPBMCs. CD69 specifically associates with S100A8/S100A9 complex as confirmed by in vitro binding and competition assay, and the treatment of CD69 with peptide-N-glycosidase significantly abolishes such association. In agreement, the glycomics analysis determines the glycosylation site and the N-glycan composition of CD69, and terminal removal of sialic acid from that N-linked glycans reverses the generation of forkhead box P3-positive Treg cells (23.21%; P < 0.05). More specifically, we showed that CD69-S100A8/S100A9 association is required for the up-regulation of suppressor of cytokine signaling 3 resulting in inhibited signaling of signal transducer and activator of transcription 3 (36.54% increase upon CD69 silencing; P < 0.01). This might in turn support the secretion of key regulator TGF-β (∼ 3.28-fold decrease upon CD69 silencing; P < 0.05), leading to reduced production of IL-4 in hPBMCs. Our results demonstrate the functional and mechanistic interplays between CD69 and S100A8/S100A9 in supporting Treg-cell differentiation.

CD69 is the crucial regulator of intestinal inflammation: a new target molecule for IBD treatment?

CD69 has been identified as an early activation marker of lymphocytes. However, recent work has indicated that CD69 plays an essential role for the regulation of inflammatory processes. Particularly, CD69 is highly expressed by lymphocytes at mucosal sites being constantly exposed to the intestinal microflora (one of the nature's most complex and most densely populated microbial habitats) and food antigens, while only a small number of circulating leukocytes express this molecule. In this review we will discuss the role of CD69 in mucosal tissue and consider CD69 as a potential target for the development of novel treatments of intestinal inflammation.

Bacterial programming of host responses: coordination between type I interferon and cell death

During mammalian infection, bacteria induce cell death from an extracellular or intracellular niche that can protect or hurt the host. Data is accumulating that associate type I interferon (IFN) signaling activated by intracellular bacteria with programmed death of immune effector cells and enhanced virulence. Multiple pathways leading to IFN-dependent host cell death have been described, and in some cases it is becoming clear how these mechanisms contribute to virulence. Yet common mechanisms of IFN-enhanced bacterial pathogenesis are not obvious and no specific interferon stimulated genes have yet been identified that cause sensitivity to pathogen-induced cell death. In this review, we will summarize some bacterial infections caused by facultative intracellular pathogens and what is known about how type I IFN signaling may promote the replication of extracellular bacteria rather than stimulate protection. Each of these pathogens can survive phagocytosis but their intracellular life cycles are very different, they express distinct virulence factors and trigger different pathways of immune activation and crosstalk. These differences likely lead to widely varying amounts of type I IFN expression and a different inflammatory environment, but these may not be important to the pathologic effects on the host. Instead, each pathogen induces programmed cell death of key immune cells that have been sensitized by the activation of the type I IFN response. We will discuss how IFN-dependent host cell death may increase host susceptibility and try to understand common pathways of pathogenesis that lead to IFN-enhanced bacterial virulence.

B cell subsets are activated and produce cytokines during early phases of Francisella tularensis LVS infection

Francisella tularensis, a facultative intracellular Gram-negative bacterium, causes the illness tularemia. The infection of mice with live vaccine strain is considered to be a model of human tularemia. F. tularensis infects predominantly such phagocytic cells as macrophages or neutrophils, but it also infects non-phagocytic hepatocytes, epithelial cells, and murine and human B cell lines. Based on work with the murine tularemia model, we report here that F. tularensis LVS infects peritoneal CD19(+) cells - exclusively B-1a cells - early after intraperitoneal infection in vivo. The peritoneal and consequently spleen CD19(+) cells are activated by the F. tularensis LVS infection to express the activation markers from MHC class II, CD25, CD54, CD69, and the co-stimulatory molecules CD80 and CD86. As early as 12 h post-infection, the peritoneal CD19(+) cells produce IFN-γ, IL-1β, IL-4, IL-6, IL-12, IL-17, IL-23, and TNF-α. The spleen CD19(+) cells respond to infection with some delay. Moreover, the F. tularensis infected A20 B cell line activates CD3(+) spleen cells isolated from naïve mice. Thus, the data presented here suggest that B cells have all the attributes to actively participate in the induction and regulation of the adaptive immune response during early stages of F. tularensis infection.

A consensus surface activation marker signature is partially dependent on human immunodeficiency virus type 1 Nef expression within productively infected macrophages

Background

The high prevalence of HIV-associated comorbidities including neurocognitive disorder, high levels of residual inflammatory mediators in the plasma and cerebrospinal fluid and the resurgence of HIV replication upon interruption of antiviral treatment in HIV-1 infected individuals, strongly suggests that despite therapy HIV persists in its cellular targets which include T-lymphocytes and cells of the myeloid lineage. These reservoirs present a major barrier against eradication efforts. Knowledge of the molecular mechanisms used by HIV to modulate innate macrophage immune responses and impair viral clearance is quite limited. To explore the role of HIV in potentially modulating macrophage function through changes in protein expression, we used single-cell analyses with flow cytometry to determine whether, in unpolarized cultures, macrophage surface marker phenotype was altered by HIV infection in a manner that was independent of host genetic background.

Results

These analyses revealed that at several time points post-infection, GFP + HIV-infected macrophages were significantly enriched in the CD14+ fraction (3 to 5-fold, p = .0001) compared to bystander, or uninfected cells in the same culture. However, the enrichment and higher levels of CD14 on HIV expressing macrophages did not depend on the production of HIV Nef. Sixty to eighty percent of macrophages productively infected with HIV after day 28 post-infection were also enriched in the population of cells expressing the activation markers CD69 (2 to 4-fold, p < .0001) and CD86 (2 to 4-fold, p < .0001 ) but suppressed amounts of CD68 (3 to 10-fold, p < .0001) compared to bystander cells. Interestingly, there was no enrichment of CD69 on the surface of HIV producing cells that lacked Nef or expressed a variant of Nef mutated in its SH3-binding domain.

Conclusions

These findings suggest that HIV actively regulates the expression of a subset of surface molecules involved in innate and inflammatory immune signaling in primary human macrophages through Nef-dependent and Nef-independent mechanisms acting within productively infected cells.

Is CD69 an effective brake to control inflammatory diseases?

Early studies described CD69 as a leukocyte activation marker, and suggested its involvement in the activation of different leukocyte subsets as well as in the pathogenesis of chronic inflammation. However, recent investigations have showed that CD69 knockout mice exhibit an enhanced or reduced susceptibility to different experimental models of inflammatory diseases, including those mediated by T helper 17 (Th17) lymphocytes. In this regard, the expression of CD69, both in Th17 lymphocytes and by a subset of regulatory T cells, has an important role in the control of the immune response and the inflammatory phenomenon. Therefore, different evidence indicates that CD69 exerts a complex immunoregulatory role in humans, and that it could be considered as a target molecule for the therapy of immune-mediated diseases.

The early activation marker CD69 regulates the expression of chemokines and CD4 T cell accumulation in intestine

Migration of naïve and activated lymphocytes is regulated by the expression of various molecules such as chemokine receptors and ligands. CD69, the early activation marker of C-type lectin domain family, is also shown to regulate the lymphocyte migration by affecting their egress from the thymus and secondary lymphoid organs. Here, we aimed to investigate the role of CD69 in accumulation of CD4 T cells in intestine using murine models of inflammatory bowel disease. We found that genetic deletion of CD69 in mice increases the expression of the chemokines CCL-1, CXCL-10 and CCL-19 in CD4⁺ T cells and/or CD4⁻ cells. Efficient in vitro migration of CD69-deficient CD4 T cells toward the chemokine stimuli was the result of increased expression and/or affinity of chemokine receptors. In vivo CD69^−/− CD4 T cells accumulate in the intestine in higher numbers than B6 CD4 T cells as observed in competitive homing assay, dextran sodium sulphate (DSS)-induced colitis and antigen-specific transfer colitis. In DSS colitis CD69^−/− CD4 T cell accumulation in colonic lamina propria (cLP) was associated with increased expression of CCL-1, CXCL-10 and CCL-19 genes. Furthermore, treatment of DSS-administrated CD69^−/− mice with the mixture of CCL-1, CXCL-10 and CCL-19 neutralizing Abs significantly decreased the histopathological signs of colitis. Transfer of OT-II×CD69^−/− CD45RB^high CD4 T cells into RAG^−/− hosts induced CD4 T cell accumulation in cLP. This study showed CD69 as negative regulator of inflammatory responses in intestine as it decreases the expression of chemotactic receptors and ligands and reduces the accumulation of CD4 T cells in cLP during colitis.

Epstein-Barr virus latent membrane protein 1 induces CD69 expression through activation of nuclear factor-κB

Latent membrane protein‑1 (LMP-1) of Epstein‑Barr virus (EBV) promotes tumorigenesis. Here, we report that LMP-1 activates the immunoregulatory molecule CD69 gene transcription through a nuclear factor-κB (NF-κB)‑dependent pathway. CD69 expression was upregulated in LMP-1‑expressing EBV-immortalized human B-cell lines and an EBV-positive Burkitt's lymphoma cell line. LMP-1 expression increased CD69 expression at the transcriptional level. CD69 promoter was regulated by LMP-1 activation of NF-κB via the carboxy-terminal activation region 1 and 2. Promoter deletion analysis indicated that two NF-κB binding sites are necessary for activation of the CD69 promoter. Electrophoretic mobility shift analysis demonstrated that LMP-1 activates both NF-κB binding sites in the CD69 promoter. This is the first report of the regulation of CD69 expression by LMP-1, and this novel finding may, thus, represent an important link between the EBV oncoprotein LMP-1 and its critical role in the development of EBV-associated diseases.

CD69 does not affect the extent of T cell priming

CD69 is rapidly upregulated on T cells upon activation. In this work we show that this is also the case for CD69 expression on dendritic cells (DC). Thus, the expression kinetics of CD69 on both cell types is reminiscent of the one of costimulatory molecules. Using mouse models of transgenic T cells, we aimed at evaluating the effect of monoclonal antibody (MAb)-based targeting and gene deficiency of CD69 expressed by either DC or T cells on the extent of antigen (Ag)-specific T cell priming, which could be the result of a putative role in costimulation as well as on DC maturation and Ag-processing and presentation. CD69 targeting or deficiency of DC did not affect their expression of costimulatory molecules nor their capacity to induce Ag-specific T cell proliferation in in vitro assays. Also, CD69 targeting or deficiency of transgenic T cells did not affect the minimal proliferative dose for different peptide agonists in vitro. In in vivo models of transgenic T cell transfer and local Ag injection, CD69 deficiency of transferred T cells did not affect the extent of the proliferative response in Ag-draining lymph nodes (LN). In agreement with these results, CD69 MAb targeting or gene deficiency of Vaccinia-virus (VACV) infected mice did not affect the endogenous formation of virus-specific CD8(+) T cell populations at the peak of the primary immune response. Altogether our results argue against a possible role in costimulation or an effect on Ag processing and presentation for CD69.

Differential effect of CD69 targeting on bystander and antigen-specific T cell proliferation

In spite of an initially proposed role as a costimulatory molecule for CD69, in vivo studies showed it as a regulator of immune responses and lymphocyte egress. We found constitutive CD69 expression by T cell subsets and pDC. We examined a possible effect of CD69 on T cell proliferation using transfer models and in vitro assays. In mice locally expressing or receiving antigen, anti-CD692.2 treatment did not affect the proliferation of antigen-specific transgenic T cells in ADLN, although we observed the presence of proliferated T cells in non-ADLN and spleen. This was not affected by FTY720 treatment and thus, not contributed by increased egress of proliferated lymphocytes from ADLN. In the absence of antigen, anti-CD69 2.2 treatment induced bystander proliferation of transferred memory phenotype T cells. This proliferation was mediated by IL-2, as it was inhibited by anti-IL-2 or anti-CD25 antibodies in vitro and by anti-CD25 antibodies in vivo. It was also dependent on CD69 expression by donor T cells and recipient cells. CD69 targeting on T cells enhanced IL-2-mediated proliferation and CD25 expression. However, it did not lead to increased early IL-2 production by T cells. No T cell subset was found to be specifically required in the recipient. Instead, CD69 targeting on pDC induced their expression of IL-2 and CD25, and pDC depletion showed that this subset was involved in the proliferation induction. These results indicate that CD69 targeting induces bystander T cell proliferation through pDC IL-2 production and T cell sensitization to IL-2 without affecting antigen-driven T cell proliferation.

Evidence for an intronic cis-regulatory element within CD69 gene

CD69 is one of the earliest proteins expressed after leukocyte activation and its engagement is essential in the control of innate and adaptive immune responses. Inducible CD69 expression is strongly controlled at the transcriptional level. The molecular basis for developmental- and stage-specific regulation in T cells is beginning to be elucidated while it remains largely unknown in the rest of immune cells. DNase I hypersensitivity experiments in lymphocytes identified a novel hypersensitive region within mouse and human intron I, which was inducible upon stimulation. In silico analysis of CD69 gene revealed that this open chromatin region was present in different cell types and was associated with positioned nucleosomes. Analysis of histone post-translational modifications of intron I indicated that acetylation and lysine 4 dimethylation of histone H3 were dynamically regulated during thymocyte development and were constitutively high in resting and stimulated mature T lymphocytes. Thus, we provide evidence for the existence of a cis-acting element in intron I that is more accessible to DNase I digestion and that it is developmentally regulated at the chromatin level.

CD69 regulates type I IFN-induced tolerogenic signals to mucosal CD4 T cells that attenuate their colitogenic potential

CD69 is highly expressed by lymphocytes at mucosal surfaces. We aimed to investigate the role of CD69 in mucosal immune responses. The expression of CD69 by CD4 T cells isolated from the spleen, mesenteric lymph nodes, small intestinal lamina propria, and colonic lamina propria was determined in specific pathogen-free B6 and TCR transgenic animals, as well as in germ-free B6 mice. Transfer colitis was induced by transplanting RAG(-/-) mice with B6 or CD69(-/-)CD45RB(high) CD4 T cells. CD69 expression by CD4 T cells is induced by the intestinal microflora, oral delivery of specific Ag, and type I IFN (IFN-I) signals. CD4 T cells from CD69(-/-) animals produce higher amounts of the proinflammatory cytokines IFN-γ, TNF-α, and IL-21, whereas the production of TGF-β1 is decreased. CD69-deficient CD4 T cells showed reduced potential to differentiate into Foxp3(+) regulatory T cells in vivo and in vitro. The transfer of CD69(-/-)CD45RB(high) CD4 T cells into RAG(-/-) hosts induced an accelerated colitis. Oral tolerance was impaired in CD69(-/-) and IFN-I receptor 1-deficient mice when compared with B6 and OT-II × RAG(-/-) animals. Polyinosinic-polycytidylic acid treatment of RAG(-/-) mice transplanted with B6 but not CD69(-/-) or IFN-I receptor 1-deficient CD45RB(high) CD4 T cells attenuated transfer colitis. CD69 deficiency led to the increased production of proinflammatory cytokines, reduced Foxp3(+) regulatory T cell induction, impaired oral tolerance, and more severe colitis. Hence, the activation Ag CD69 plays an important role in regulating mucosal immune responses.

Activated lymphocytes and high liver expression of IFN-γ are associated with fulminant hepatic failure in patients

BACKGROUND & AIMS

To study immunological mechanisms of fulminant hepatic failure (FHF) derived from extensive liver lesions, 14 patients with FHF induced by different aetiologies were investigated by observance of both lymphocyte phenotyping and cytokine levels.

METHODS

Five patients bearing benign acute hepatitis B (AHB) and seven healthy liver donors (HC) were used as controls. Samples of liver and blood from both FHF patients and HC were obtained during transplantation procedures. Plasma levels of IL-1β, IL-4, IL-6, IL-8, IL-10, IFN-γ, TNF-α, MCP-1, RANTES and MIP-1α were quantified using a multiplex immunoassay. Cell characterization was carried out by flow cytometry. IFN-γ staining was performed on liver sections using immunofluorescence methods.

RESULTS

An increase of peripheral frequency of natural killer (NK) cells expressing early activation markers (CD69, HLA-DR and CD38) and adhesion molecule CD44 was observed in FHF patients. Elevated frequency of T lymphocytes CD4(+) and CD8(+) expressing CD38 and adhesion molecules CD29 and CD44 was also observed in FHF. Additionally, an increase of natural killer T cells (NKT) was detected in FHF patients. High plasma cytokine levels were not statistically different between FHF and AHB patients. In comparison to HC, a strong liver expression of IFN-γ was detected in FHF patients. The increased frequency of CD4(+) CD44(+) and IL-8 cytokine was found in patients with poor prognosis.

CONCLUSIONS

These findings indicate the involvement of NK and NKT cells as well as T lymphocytes CD4(+) and CD8(+) in the inflammatory process inducing FHF, confirmed by the high hepatic expression of IFN-γ.

Distinct expression patterns of CD69 in mucosal and systemic lymphoid tissues in primary SIV infection of rhesus macaques

Although the intestinal tract plays a major role in early human immunodeficiency virus (HIV) infection, the role of immune activation and viral replication in intestinal tissues is not completely understood. Further, increasing evidence suggests the early leukocyte activation antigen CD69 may be involved in the development or regulation of important T cell subsets, as well as a major regulatory molecule of immune responses. Using the simian immunodeficiency virus (SIV) rhesus macaque model, we compared expression of CD69 on T cells from the intestine, spleen, lymph nodes, and blood of normal and SIV-infected macaques throughout infection. In uninfected macaques, the majority of intestinal lamina propria CD4+ T cells had a memory (CD95+) phenotype and co-expressed CD69, and essentially all intestinal CCR5+ cells co-expressed CD69. In contrast, systemic lymphoid tissues had far fewer CD69+ T cells, and many had a naïve phenotype. Further, marked, selective depletion of intestinal CD4+CD69+ T cells occurred in early SIV infection, and this depletion persisted throughout infection. Markedly increased levels of CD8+CD69+ T cells were detected after SIV infection in virtually all tissues, including the intestine. Further, confocal microscopy demonstrated selective, productive infection of CD3+CD69+ T cells in the intestine in early infection. Combined, these results indicate CD69+CD4+ T cells are a major early target for viral infection, and their rapid loss by direct infection may have profound effects on intestinal immune regulation in HIV infected patients.

NSOM/QD-based fluorescence-topographic image fusion directly reveals nano-spatial peak-valley polarities of CD69 and CD71 activation molecules on cell-membrane fluctuations during T-cell activation

Nano-spatial distribution of cell surface molecules on cell membrane fluctuations during T-cell activation has not been reported. In this study, we innovated application of near-field scanning optical microscopy (NSOM)/quantum dots (QDs)-based nanotechnology through three-dimensional image fusion algorithm to merge the simultaneously obtained dual-color fluorescence information and three-dimensional topography. This novel imaging system made it possible to visualize nano-spatial distribution and organization of early-activation molecules CD69 and late-activation molecules CD71 on cell-membrane fluctuations during T-cell activation. Interestingly, most CD69 molecules were clustered to form 250-500nm nano-domains polarizing predominantly in the peak of the cell-membrane fluctuations. In contrast, although CD71 molecules were also clustered as 250-500nm nano-domains, they polarized dominantly in the valley of the cell-membrane fluctuations. The peak-valley polarities of CD69 nano-domains and CD71 nano-domains implied their different functions. CD69 nano-domains polarizing on membrane-peak fluctuations might serve as transient platforms driving TCR/CD3-induced signaling and activation, whereas CD71 nano-domains distributing in the membrane-valley fluctuations appeared to facilitate iron uptake for increased metabolisms in T-cell activation. Importantly, this NSOM/QD-based fluorescence-topographic image fusion provides a powerful tool to visualize nano-spatial distribution of cell-surface molecules on cell-membrane fluctuations and enable better understanding of distribution-function relationship.