T‐cell receptor activation of human CD4+ T cells shifts the innate TLR response from CXCL8hiIFN‐γnull to CXCL8loIFN‐γhi

Toll‐like receptors (TLRs) play a major part in providing innate immunity against pathogenic microorganisms. Recent studies show that these receptors are also expressed on T cells, which are the sentinels of adaptive immunity. Here, we have investigated the regulatory role of the T‐cell receptor in the functioning of these innate receptors in T cells. We show that freshly isolated human CD4⁺ T cells readily secrete the neutrophil chemoattractant CXCL8 upon activation with the TLR ligands Pam3CSK and flagellin. In contrast, TCR‐activated cells secrete considerably less CXCL8 but start producing IFN‐γ upon stimulation with TLR agonists in the absence of concomitant TCR engagement. These T cells show increased activation of p38 and JNK MAP‐kinases in response to TLR stimulation, and inhibition of p38 abrogates TLR‐induced IFN‐γ secretion. The shifting of the T‐cell innate immune response from CXCL8^hiIFN‐γ^null in freshly isolated to CXCL8^loIFN‐γ^hi in activated T cells is also observed in response to endogenous innate stimulus, IL‐1. These results suggest that the innate immune response of human CD4⁺ T cells switches from a proinflammatory to an effector type following activation of these cells through the antigen receptor.     

B cells expressing IFN‐γ suppress Treg‐cell differentiation and promote autoimmune experimental arthritis

Clinical efficacy in the treatment of rheumatoid arthritis with anti‐CD20 (Rituximab)‐mediated B‐cell depletion has garnered interest in the mechanisms by which B cells contribute to autoimmunity. We have reported that B‐cell depletion in a murine model of proteoglycan‐induced arthritis (PGIA) leads to an increase in Treg cells that correlate with decreased autoreactivity. Here, we demonstrate that the increase in Treg cells after B‐cell depletion is due to an increase in the differentiation of naïve CD4⁺ T cells into Treg cells. Since the development of PGIA is dependent on IFN‐γ and B cells are reported to produce IFN‐γ, we hypothesized that B‐cell‐specific IFN‐γ plays a role in the development of PGIA. Accordingly, mice with B‐cell‐specific IFN‐γ deficiency were as resistant to the induction of PGIA as mice that were completely IFN‐γ deficient. Importantly, despite a normal frequency of IFN‐γ‐producing CD4⁺ T cells, B‐cell‐specific IFN‐γ‐deficient mice exhibited a higher percentage of Treg cells compared with that in WT mice. These data indicate that B‐cell IFN‐γ production inhibits Treg‐cell differentiation and exacerbates arthritis. Thus, we have established that IFN‐γ, specifically derived from B cells, uniquely contributes to the pathogenesis of autoimmunity through prevention of immunoregulatory mechanisms.     

A20 deletion in T cells modulates acute graft‐versus‐host disease in mice

The NF‐κB regulator A20 limits inflammation by providing negative feedback in myeloid cells and B cells. Functional lack of A20 has been linked to several inflammatory and autoimmune diseases. To define how A20 affects the functionality of T effector cells in a highly inflammatory environment, we performed conventional allogeneic hematopoietic stem cell transplantation (allo‐HSCT) with A20‐deficient CD4⁺ and CD8⁺ donor T cells in mice. Severity and mortality of graft‐versus‐host disease (GVHD) after allo‐HSCT was drastically reduced in recipients transplanted with conventional doses of A20‐deficient T cells. Consistently, we found that the A20‐deficient donor T‐cell compartment was strongly diminished at various timepoints after allo‐HSCT. However, proportionally more A20‐deficient donor T cells produced IFN‐γ and systemic inflammation was elevated early after allo‐HSCT. Consequently, increasing the dose of transplanted A20‐deficient T cells reversed the original phenotype and resulted in enhanced GVHD mortality compared to recipients that received A20^+/+ T cells. Still, A20‐deficient T cells, activated either through T cell receptor‐dependent or ‐independent mechanisms, were less viable than control A20^+/+ T cells, highlighting that A20 balances both, T‐cell activation and survival. Thus, our findings suggest that targeting A20 in T cells may allow to modulate T‐cell‐mediated inflammatory diseases like GVHD.     

Mycobacterium tuberculosis‐specific CD4+ T‐cell response is increased,and Treg cells decreased,in anthelmintic‐treated patients with latent TB

In many settings, adults with active or latent tuberculosis will also be coinfected with helminths. Our study aimed to investigate how anthelmintic treatment modulates antimycobacterial immunity, in a setting where helminth reinfection should not occur. We investigated the potential impact of helminth infection on immune responses to Mycobacterium tuberculosis (Mtb) in patients with latent Mtb infection with or without helminth infection (Strongyloides or Schistosoma), and tested T‐cell responses before and after anthelmintic treatment. The study was performed in migrants resident in the United Kingdom, where reexposure and reinfection following anthelmintic treatment would not occur. The frequency of CD4⁺IFN‐γ⁺ T cells was measured following stimulation with Mtb Purified Protein Derivative or ESAT‐6/CFP‐10 antigen, and concentrations of IFN‐γ in culture supernatants measured by ELISA and multiplex bead array. Helminth infection was associated with a lower frequency of CD4⁺IFN‐γ⁺ T cells, which increased following treatment. Patients with helminth infection showed a significant increase in CD4⁺FoxP3⁺ T cells (Treg) compared to those without helminth infection. There was a decrease in the frequency of Treg cells, and an associated increase in CD4⁺IFN‐γ⁺ T cells after the anthelmintic treatment. Here, we show a potential role of Treg cells in reducing the frequency and function of antimycobacterial CD4⁺IFN‐γ⁺ T cells, and that these effects are reversed after anthelmintic treatment.     

Cord Blood Monocytes,Neutrophils and Lymphocytes from Preterm and Full‐Term Neonates Show Multiple Aberrations in Signalling Profiles Measured Using Phospho‐Specific Whole‐Blood Flow Cytometry

Immaturity of the immune system renders newborns susceptible to infections. We searched for aberrations in leucocyte signalling profiles, using phospho‐specific whole‐blood flow cytometry, in cord blood of nine preterm (two born before 32nd gestational week) and nine full‐term infants, born by caesarean section. Thirteen adults served as reference subjects. Monocyte NF‐κB phosphorylation following tumour necrosis factor (TNF) or bacterial stimulation was higher in preterm neonates than in full‐term neonates or adults, p38 phosphorylation following bacterial stimulation was higher in both preterm and full‐term neonates than in adults, while STAT1 phosphorylation by IFN‐γ or IL‐6, STAT3 phosphorylation by IL‐6 and STAT5 phosphorylation by GM‐CSF were lower in both full‐term and preterm neonates than in adults. Neutrophil STAT1 and STAT3 phosphorylation following IFN‐γ stimulation and STAT5 phosphorylation following GM‐CSF stimulation were lower in newborn neonates than in adults. In both CD3⁺CD4⁺ and CD3⁺CD8⁺ lymphocytes, NF‐κB phosphorylation by TNF was higher and STAT5 phosphorylation by IL‐2 was lower in preterm and full‐term newborns than in adults. STAT6 phosphorylation by IL‐4 was comparable in monocytes and lymphocytes of newborns and adults. The results suggest that innate immune signalling pathways responding to inflammatory stimuli are strongly functional in leucocytes of preterm neonates, which may render these neonates susceptible to inappropriate tissue injury. In leucocytes of both preterm and full‐term newborns, responses needed against intracellular pathogens, and regulatory functions show immaturities, possibly contributing to worse control of infections.     

CD70 and IFN‐1 selectively induce eomesodermin or T‐bet and synergize to promote CD8+ T‐cell responses

CD70‐mediated stimulation of CD27 is an important cofactor of CD4⁺ T‐cell licensed dendritic cells (DCs). However, it is unclear how CD70‐mediated stimulation of T cells is integrated with signals that emanate from signal 3 pathways, such as type‐1 interferon (IFN‐1) and IL‐12. We find that while stimulation of CD27 in isolation drives weak Eomesodermin^hiT‐bet^lo CD8⁺ T‐cell responses to OVA immunization, profound synergistic expansion is achieved by cotargeting TLR. This cooperativity can substantially boost antiviral CD8⁺ T‐cell responses during acute infection. Concomitant stimulation of TLR significantly increases per cell IFN‐γ production and the proportion of the population with characteristics of short‐lived effector cells, yet also promotes the ability to form long‐lived memory. Notably, while IFN‐1 contributes to the expression of CD70 on DCs, the synergy between CD27 and TLR stimulation is dependent upon IFN‐1's effect directly on CD8⁺ T cells, and is associated with the increased expression of T‐bet in T cells. Surprisingly, we find that IL‐12 fails to synergize with CD27 stimulation to promote CD8⁺ T‐cell expansion, despite its capacity to drive effector CD8⁺ T‐cell differentiation. Together, these data identify complex interactions between signal 3 and costimulatory pathways, and identify opportunities to influence the differentiation of CD8⁺ T‐cell responses.     

Progesterone promotes maternal–fetal tolerance by reducing human maternal T‐cell polyfunctionality and inducing a specific cytokine profile

Progesterone is a steroid hormone essential for the maintenance of human pregnancy, and its actions are thought to include promoting maternal immune tolerance of the semiallogenic fetus. We report that exposure of maternal T cells to progesterone at physiological doses induced a unique skewing of the cytokine production profile of CD4⁺ and CD8⁺ T cells, with reductions not only in potentially deleterious IFN‐γ and TNF‐α production but also in IL‐10 and IL‐5. Conversely, production of IL‐4 was increased. Maternal T cells also became less polyfunctional, focussing cytokine production toward profiles including IL‐4. This was accompanied by reduced T‐cell proliferation. Using fetal and viral antigen‐specific CD8⁺ T‐cell clones, we confirmed that this as a direct, nonantigen‐specific effect. Yet human T cells lacked conventional nuclear progesterone receptors, implicating a membrane progesterone receptor. CD4⁺ and CD8⁺ T cells responded to progesterone in a dose‐dependent manner, with subtle effects at concentrations comparable to those in maternal blood, but profound effects at concentrations similar to those at the maternal–fetal interface. This characterization of how progesterone modulates T‐cell function is important in understanding the normal biology of pregnancy and informing the rational use of progesterone therapy in pregnancies at risk of fetal loss.     

Thymus‐resident memory CD8+ T cells mediate local immunity

The thymus is a primary lymphoid organ responsible for production and selection of T cells. Nonetheless, mature T cells and in particular activated T cells can reenter the thymus. Here, we identified memory CD8⁺ T cells specific for lymphocytic choriomeningitis virus or vaccinia virus in the thymus of mice long‐time after the infection. CD8⁺ T cells were mainly located in the thymic medulla, but also in the cortical areas. Interestingly, virus‐specific memory CD8⁺ T cells in the thymus expressed the cell surface markers CD69 and CD103 that are characteristic of tissue‐resident memory T cells in a time‐dependent manner. Kinetic analyses and selective depletion of peripheral CD8⁺ T cells by antibodies further revealed that thymic virus‐specific memory CD8⁺ T cells did not belong to the circulating pool of lymphocytes. Finally, we demonstrate that these thymus‐resident virus‐specific memory CD8⁺ T cells efficiently mounted a secondary proliferative response, exhibited immediate effector functions and were able to protect the thymus from lymphocytic choriomeningitis virus reinfection. In conclusion, the present study not only describes for the first time virus‐specific memory CD8⁺ T cells with characteristics of tissue‐resident memory T (T_RM) cells in a primary lymphoid organ but also extends our knowledge about local T‐cell immunity in the thymus.     

Early effector maturation of naïve human CD8+ T cells requires mitochondrial biogenesis

The role of mitochondrial biogenesis during naïve to effector differentiation of CD8⁺ T cells remains ill explored. In this study, we describe a critical role for early mitochondrial biogenesis in supporting cytokine production of nascent activated human naïve CD8⁺ T cells. Specifically, we found that prior to the first round of cell division activated naïve CD8⁺ T cells rapidly increase mitochondrial mass, mitochondrial respiration, and mitochondrial reactive oxygen species (mROS) generation, which were all inter‐linked and important for CD8⁺ T cell effector maturation. Inhibition of early mitochondrial biogenesis diminished mROS dependent IL‐2 production – as well as subsequent IL‐2 dependent TNF, IFN‐γ, perforin, and granzyme B production. Together, these findings point to the importance of mitochondrial biogenesis during early effector maturation of CD8⁺ T cells.     

Serotonin decreases the production of Th1/Th17 cytokines and elevates the frequency of regulatory CD4+ T‐cell subsets in multiple sclerosis patients

Excessive levels of proinflammatory cytokines in the CNS are associated with reduced serotonin (5‐HT) synthesis, a neurotransmitter with diverse immune effects. In this study, we evaluated the ability of exogenous 5‐HT to modulate the T‐cell behavior of patients with MS, a demyelinating autoimmune disease mediated by Th1 and Th17 cytokines. Here, 5‐HT attenuated, in vitro, T‐cell proliferation and Th1 and Th17 cytokines production in cell cultures from MS patients. Additionally, 5‐HT reduced IFN‐γ and IL‐17 release by CD8⁺ T cells. By contrast, 5‐HT increased IL‐10 production by CD4⁺ T cells from MS patients. A more accurate analysis of these IL‐10‐secreting CD4⁺ T cells revealed that 5‐HT favors the expansion of FoxP3⁺CD39⁺ regulatory T cells (Tregs) and type 1 regulatory T cells. Notably, this neurotransmitter also elevated the frequency of Treg17 cells, a novel regulatory T‐cell subset. The effect of 5‐HT in upregulating CD39⁺ Treg and Treg17 cells was inversely correlated with the number of active brain lesions. Finally, in addition to directly reducing cytokine production by purified Th1 and Th17 cells, 5‐HT enhanced in vitro Treg function. In summary, our data suggest that serotonin may play a protective role in the pathogenesis of MS.     

TGF‐β induces the differentiation of human CXCL13‐producing CD4+ T cells

In the ectopic lymphoid‐like structures present in chronic inflammatory conditions such as rheumatoid arthritis, a subset of human effector memory CD4⁺ T cells that lacks features of follicular helper T (Tfh) cells produces CXCL13. Here, we report that TGF‐β induces the differentiation of human CXCL13‐producing CD4⁺ T cells from naïve CD4⁺ T cells. The TGF‐β‐induced CXCL13‐producing CD4⁺ T cells do not express CXCR5, B‐cell lymphoma 6 (BCL6), and other Tfh‐cell markers. Furthermore, expression levels of CD25 (IL‐2Rα) in CXCL13‐producing CD4⁺ T cells are significantly lower than those in FoxP3⁺ in vitro induced Treg cells. Consistent with this, neutralization of IL‐2 and knockdown of STAT5 clearly upregulate CXCL13 production by CD4⁺ T cells, while downregulating the expression of FoxP3. Furthermore, overexpression of FoxP3 in naïve CD4⁺ T cells downregulates CXCL13 production, and knockdown of FoxP3 fails to inhibit the differentiation of CXCL13‐producing CD4⁺ T cells. As reported in rheumatoid arthritis, proinflammatory cytokines enhance secondary CXCL13 production from reactivated CXCL13‐producing CD4⁺ T cells. Our findings demonstrate that CXCL13‐producing CD4⁺ T cells lacking Tfh‐cell features differentiate via TGF‐β signaling but not via FoxP3, and exert their function in IL‐2‐limited but TGF‐β‐rich and proinflammatory cytokine‐rich inflammatory conditions.     

Role of CD4 T cell helper subsets in immune response and deviation of CD8 T cells in mice*

The ability of different CD4⁺ T cell subsets to help CD8⁺ T‐cell response is not fully understood. Here, we found using the murine system that Th17 cells induced by IL‐1β, unlike Th1, were not effective helpers for antiviral CD8 responses as measured by IFNγ‐producing cells or protection against virus infection. However, they skewed CD8 responses to a Tc17 phenotype. Thus, the apparent lack of help was actually immune deviation. This skewing depended on both IL‐21 and IL‐23. To overcome this effect, we inhibited Th17 induction by blocking TGF‐β. Anti‐TGF‐β allowed the IL‐1β adjuvant to enhance CD8⁺ T‐cell responses without skewing the phenotype to Tc17, thereby providing an approach to harness the benefit of common IL‐1‐inducing adjuvants like alum without immune deviation.     

IFN‐γ stimulates CpG‐induced IL‐10 production in B cells via p38 and JNK signalling pathways

The production of IL‐10, a potent immunosuppressive cytokine, must be strictly regulated to ensure a balanced immune response. IFN‐γ, a key cytokine in multiple immune processes and pathologies, is known as an inhibitor of IL‐10 production by monocytes and macrophages, but also has some regulatory functions. In the present study, we explored the role of IFN‐γ on Toll‐like receptor (TLR)‐induced IL‐10 production in murine peritoneal and spleen cells and in human peripheral blood mononuclear cells. IFN‐γ inhibited IL‐10 production induced by TLR2, TLR3, TLR4 and TLR7/8 agonists, but stimulated IL‐10 production when cells were triggered with CpG oligodeoxynucleotides, a specific TLR9 agonist. The stimulatory effect of IFN‐γ on TLR9‐induced IL‐10 was restricted to B cells. In line with the increased IL‐10, B cells stimulated with CpG and IFN‐γ profoundly inhibited CD4 T cell proliferation. Further research into the mechanisms involved, revealed that the mitogen‐activated protein kinases p38 and JNK are essential players in this stimulatory effect, and that the phosphatase MKP1 – an inhibitor of p38 and JNK activity – is downregulated after combined stimulation with IFN‐γ and CpG. Our data may represent a novel immunoregulatory role of IFN‐γ in B cells after triggering of TLR9, by stimulating IL‐10 production.     

Brain‐resident memory CD8+ T cells induced by congenital CMV infection prevent brain pathology and virus reactivation

Congenital HCMV infection is a leading infectious cause of long‐term neurodevelopmental sequelae. Infection of newborn mice with mouse cytomegalovirus (MCMV) intraperitoneally is a well‐established model of congenital human cytomegalovirus infection, which best recapitulates the hematogenous route of virus spread to brain and subsequent pathology. Here, we used this model to investigate the role, dynamics, and phenotype of CD8⁺ T cells in the brain following infection of newborn mice. We show that CD8⁺ T cells infiltrate the brain and form a pool of tissue‐resident memory T cells (T_RM cells) that persist for lifetime. Adoptively transferred virus‐specific CD8⁺ T cells provide protection against primary MCMV infection in newborn mice, reduce brain pathology, and remain in the brain as T_RM cells. Brain CD8⁺ T_RM cells were long‐lived, slowly proliferating cells able to respond to local challenge infection. Importantly, brain CD8⁺ T_RM cells controlled latent MCMV and their depletion resulted in virus reactivation and enhanced inflammation in brain.