T helper cell differentiation more than just cytokines

Role of Th17 cells in the pathogenesis of rheumatoid arthritis

Since early description of CD4/CD8 T cell duality, continuous discovery of functional T lymphocyte subsets and their related cytokines constitutes major progress in our understanding of the immune response. T-lymphocyte derived lymphokines and environmental cytokines are essential for both innate and antigen-specific immune responses to a wide variety of agents. Following immune battle and aggression overcome, cytokines may return against neighbored cells/organs, causing pathogenic hypersensitivity reactions, including autoimmune diseases. Due to their cytokine production, CD4⁺ T helper lymphocyte subsets may be considered as one the major players of the immune response. Among CD4⁺ T cell subsets, the identification of interleukin-17-producing cells (Th17) led to better understanding of coordinated cytokine involvement during inflammatory reactions together with the subsequent clarification of complex interactions between these mediators. In this review, we discuss Th17 cell differentiation, functions, and the role of this cell subset during rheumatoid arthritis pathogenesis together with therapeutic strategies to control these cells.

Ikaros sets the potential for Th17 lineage gene expression through effects on chromatin state in early T cell development

Th17 cells are important effectors of immunity to extracellular pathogens, particularly at mucosal surfaces, but they can also contribute to pathologic tissue inflammation and autoimmunity. Defining the multitude of factors that influence their development is therefore of paramount importance. Our previous studies using Ikaros(-/-) CD4+ T cells implicated Ikaros in Th1 versus Th2 lineage decisions. Here we demonstrate that Ikaros also regulates Th17 differentiation through its ability to promote expression of multiple Th17 lineage-determining genes, including Ahr, Runx1, Rorc, Il17a, and Il22. Ikaros exerts its influence on the chromatin remodeling of these loci at two distinct stages in CD4+ T helper cell development. In naive cells, Ikaros is required to limit repressive chromatin modifications at these gene loci, thus maintaining the potential for expression of the Th17 gene program. Subsequently, Ikaros is essential for the acquisition of permissive histone marks in response to Th17 polarizing signals. Additionally, Ikaros represses the expression of genes that limit Th17 development, including Foxp3 and Tbx21. These data define new targets of the action of Ikaros and indicate that Ikaros plays a critical role in CD4+ T cell differentiation by integrating specific cytokine cues and directing epigenetic modifications that facilitate activation or repression of relevant genes that drive T cell lineage choice.

Regulatory dendritic cell expression of MHCII and IL-10 are jointly requisite for induction of tolerance in a murine model of OVA-asthma

BACKGROUND

Allergen-presenting dendritic cells differentiated with IL-10 (DC10) reverse the asthma phenotype in mice by converting their Th2 cells to regulatory T cells (Tregs). DC10 express elevated levels of IL-10, but substantially reduced levels of MHCII and costimulatory molecules, so the relationships between these factors with each other and tolerogenicity have not been clearly elucidated.

METHODS

We assessed the roles of these inputs in DC10 reversal of OVA-associated asthma-like disease by treating affected mice with OVA-pulsed DC10 generated from wild-type or IL-10-sufficient MHCII(-/-) or CD80/CD86(-/-) mice, or with MHCII-intact IL-10-silenced DC10.

RESULTS

IL-10 silencing did not discernibly affect the cells' immunobiology (e.g., costimulatory molecules, chemokines), but it eliminated IL-10 secretion and the cell's abilities to induce tolerance, as determined by assessments of airway hyper-responsiveness, eosinophilia, and Th2 responses to recall OVA challenge. MHCII(-/-) DC10 expressed normal levels of IL-10, but, nevertheless, were unable to induce allergen tolerance in asthma phenotype mice, while tolerance induced by CD80/CD86(-/-) DC10 was attenuated but not eliminated. We also assessed the induction of multiple Treg cell markers (e.g., ICOS, PD-1, GITR) on pulmonary CD25(+) Foxp3(+) cells in the treated mice. Wild-type DC10 treatments upregulated expression of each marker, while neither IL-10-silenced nor MHCII(-/-) DC10 did so, and the CD80/86(-/-) DC10 induced an intermediate Treg cell activation phenotype.

CONCLUSION

Both IL-10 and MCHII expression by DC10 are requisite, but not sufficient for tolerance induction, suggesting that DC10 and Th2 effector T cells must be brought together in a cognate fashion in order for their IL-10 to induce tolerance.

The role and potential therapeutic application of myeloid-derived suppressor cells in TNBS-induced colitis

MDSCs, a heterogeneous population of cells that expand during many pathogenic conditions, have remarkable abilities to suppress T cell responses. Their role in murine colitis, induced by TNBS and therapeutic application, remains unclear. Murine colitis was induced through intrarectally administrating TNBS, twice. MDSCs in spleen and colonic LPMCs were identified using flow cytometric analysis. In adoptive transfer, MDSCs were isolated from spleen after TNBS challenges by using microbeads or generated in vitro by coculturing bone marrow cells with HSCs and then transferred into naïve mice. Two hours later, mice were then challenged with TNBS, once/week for 2 weeks. The mice were killed four days after the second TNBS delivery, and intestinal inflammation and cytokine levels and MDSC percentages were evaluated. The percentages of CD11b+Gr-1+MDSCs and subsets (CD11b+Ly6C+ and CD11b+Ly6G+MDSCs) were increased in spleen and/or colonic LPMCs in colitis mice and also correlated with the severity of intestinal inflammation. MDSCs isolated from colitis mice suppressed the proliferation of splenocytes in vitro. Adoptive transfer of MDSCs, isolated from colitis mice or generated in vitro, decreased intestinal inflammation, levels of IFN-γ, IL-17, and TNF, and percentages of spleen MDSCs when compared with controls. MDSCs that have inhibitory function in vitro and in vivo are increased and correlated with intestinal inflammation, suggesting that they may be used as a biomarker of disease activity and a cell-based biotherapy in IBD.

IL-17 in the rheumatologist's line of sight

Over the past decades, the identification of several new cytokines, including interleukin (IL)-17 and IL-23, and of new T helper cell subsets, including Th17 cells, has changed the vision of immunological processes. The IL-17/Th17 pathway plays a critical role during the development of inflammation and autoimmunity, and targeting this pathway has become an attractive strategy for a number of diseases. This review aims to describe the effects of IL-17 in the joint and its roles in the development of autoimmune and inflammatory arthritis. Furthermore, biotherapies targeting directly or indirectly IL-17 in inflammatory rheumatisms will be developed.

Th2-type innate immune responses mediated by natural helper cells

Natural helper (NH) cells are a newly identified innate lymphocyte population that responds to a combination of interleukin (IL)-2 and either IL-25 or IL-33 to produce large amounts of T helper cell type 2 (Th2) cytokines. NH cells have been identified in fat-associated lymphoid clusters (FALCs), produce Th2 cytokines constitutively without any stimulation, and support the self-renewal of B1 cells and IgA production by B cells. Large amounts of IL-5 and IL-13 produced upon helminth infection or in response to IL-33 can induce eosinophilia and goblet cell hyperplasia in the lung and intestine; these cytokines, which activate NH cells, play important roles in antihelminth immunity and allergic diseases such as asthma.

Epigenetics and the adaptive immune response

Cells of the adaptive immune response undergo dynamic epigenetic changes as they develop and respond to immune challenge. Plasticity is a necessary prerequisite for the chromosomal dynamics of lineage specification, development, and the immune effector function of the mature cell types. The alterations in DNA methylation and histone modification that characterize activation may be integral to the generation of immunologic memory, thereby providing an advantage on secondary exposure to pathogens. While the immune system benefits from the dynamic nature of the epigenome, such benefit comes at a cost - increased likelihood of disease-causing mutation.

An IL-17 peptide-based and virus-like particle vaccine enhances the bioactivity of IL-17 in vitro and in vivo

AIMS

To develop an IL-17 peptide-based virus-like particle vaccine that elicits autoantibodies to IL-17 and to evaluate the effects of the vaccine in mice with experimental colitis.

MATERIALS & METHODS

Recombinant IL-17 vaccines were constructed by inserting selected peptides derived from mouse IL-17 into the carrier protein, hepatitis B core antigen, using molecular engineering methods. To evaluate the in vivo effects of the vaccine, mice with 2,4,6-trinitrobenzene sulfonic acid-induced chronic colitis were injected three times with the vaccine, carrier or saline after the second delivery of 2,4,6-trinitrobenzene sulfonic acid. Colon inflammation and fibrosis were evaluated by histological examination. Serum IL-17-specific IgG and colon-tissue cytokine levels were measured by ELISA. In vitro inhibition tests of sera from vaccine-immunized mice were performed using IL-17-induced IL-6 production by NIH 3T3 cells and IL-17-induced TNF production by macrophages.

RESULTS

Immunization with the vaccine without the use of adjuvants induced high-titered and long-lasting antibodies to IL-17. Unexpectedly, vaccinated mice exhibited increases in colon inflammation, collagen deposition, levels of TNF and IL-17 cytokines compared with carrier and saline groups. Furthermore, in vitro study revealed that serum IL-17-specific IgG from vaccine-immunized mice significantly enhanced IL-17-induced IL-6 production and IL-17-induced TNF production dose-dependently.

CONCLUSION

The IL-17 peptide-based vaccine enhances the bioactivity of IL-17 in vitro and in vivo, providing a potential immunotherapy for treatment of diseases associated with insufficient IL-17 production, such as hyper-IgE syndrome.

Natural helper cells and TH2-type innate immunity

Natural helper (NH) cells are a newly identified innate lymphocyte population, which respond to a combination of interleukin (IL)-2 and IL-25 or IL-33 to produce large amounts of TH2 cytokines, most notably, IL-5 and IL-13. We identified NH cells in lymphoid clusters in adipose tissues, which we termed fat-associated lymphoid clusters. IL-5 and IL-13 produced by activated NH cells induce eosinophilia and goblet cell hyperplasia, respectively, and play an important role in anti-helminth immunity and allergic diseases, such as asthma. In addition, NH cells produce TH2 cytokines constitutively in the absence of stimulation and support the self-renewal of B1 cells and IgA production by B cells. After our identification of NH cells, other groups have also reported novel TH2 cytokine-producing cells, such as nuocytes, and innate helper type 2 cells. There are similarities and differences between these newly identified cell populations and NH cells. Multipotent progenitor cell type 2 (MPP) cells can differentiate to other myeloid cells, making this a distinct cell type from the others. MPP cells, nuocytes, and innate helper type 2 cells respond to IL-25 alone in vivo, whereas NH cells do not respond to IL-25 without IL-2, although they respond strongly to IL-33. Localization of NH cells in fat-associated lymphoid clusters is an intriguing difference compared with the other cell types, which are found in the lymph node and/or spleen. This article summarizes current information regarding the emerging field of TH2-type innate lymphocytes.

Activation of immune responses to brain antigens after stroke

Infection is common after stroke and is independently associated with a worse outcome. The predisposition to infection following stroke is in part related to a sympathetically mediated suppression of the peripheral immune response. The teleological explanation for this immune dysfunction is that it serves to prevent autoimmune responses to brain antigens. We believe that the systemic immune response in patients who develop infection, however, thwarts this seemingly protective response and predisposes to central nervous system autoimmunity. These autoimmune responses may mediate, at least in part, the worse outcome associated with post-stroke infection.

The role of costimulatory molecules in directing the functional differentiation of alloreactive T helper cells

Costimulatory molecules are a heterogenous group of cell surface molecules that act to amplify or counteract the initial activating signals provided to T cells from the T cell receptor following its interaction with an antigen/major histocompatibility complex, thereby influencing T cell differentiation and fate. Although costimulation was previously thought to be indispensable for T cell activation at all stages of development, it is now known that the requirements for costimulation, and the costimulatory molecules involved, vary according to the stage of T cell differentiation. The ability to influence T cell fate is of paramount interest in the field of transplantation as we seek therapeutic options that inhibit detrimental alloimmune responses whilst simultaneously promoting allograft tolerance. As with many immune mechanisms, there is a degree of functional overlap between certain costimulatory molecules, whereas some have diametrically opposite effects on different T cell subsets despite sharing common ligands. This is a critical point when considering these molecules as therapeutic targets in transplantation, as blockade of a costimulatory pathway, although desirable in itself, may prevent the ligation of an essential regulatory coinhibitory molecule. This review discusses the T helper cell lineages pertinent to transplantation and the costimulatory molecules involved in their differentiation.

The ex vivo production of IL-6 and IL-21 by CD4+ T cells is directly associated with neurological disability in neuromyelitis optica patients

Neuromyelitis optica (NMO), also known as Devic's disease, is an autoimmune, inflammatory disorder of the central nervous system (CNS) in which the immune system attacks myelin of the neurons located at the optic nerves and spinal cord, thus producing a simultaneous or sequential optic neuritis and myelitis. The objective of this study was evaluated the background T-cell function of patients suffering from neuromyelitis optica (NMO), an autoimmune disorder of the central nervous system. In our study, the in vitro T cell proliferation and the production of Th1 cytokines were significantly lower in cell cultures from NMO patients, as compared with healthy individuals. In contrast, a dominant Th17-like phenotype, associate with higher IL-23 and IL-6 production by LPS-activated monocytes, was observed among NMO patients. The release of IL-21 and IL-6 by polyclonally activated CD4+ T cells was directly correlated to neurological disability. In addition, the in vitro release of IL-21, IL-6 and IL-17 was significantly more resistant to glucocorticoid inhibition in NMO patients. In conclusion, the results indicate dominant Th17-related response in NMO patients that was directly proportional to neurological disability. Furthermore, our results can help to explain why NMO patients trend to be more refractory to corticoid treatment.

Tc17 cells mediate vaccine immunity against lethal fungal pneumonia in immune deficient hosts lacking CD4+ T cells

Vaccines may help reduce the growing incidence of fungal infections in immune-suppressed patients. We have found that, even in the absence of CD4⁺ T-cell help, vaccine-induced CD8⁺ T cells persist and confer resistance against Blastomyces dermatitidis and Histoplasma capsulatum. Type 1 cytokines contribute to that resistance, but they also are dispensable. Although the role of T helper 17 cells in immunity to fungi is debated, IL-17 producing CD8⁺ T cells (Tc17 cells) have not been investigated. Here, we show that Tc17 cells are indispensable in antifungal vaccine immunity in hosts lacking CD4⁺ T cells. Tc17 cells are induced upon vaccination, recruited to the lung on pulmonary infection, and act non-redundantly in mediating protection in a manner that requires neutrophils. Tc17 cells did not influence type I immunity, nor did the lack of IL-12 signaling augment Tc17 cells, indicating a distinct lineage and function. IL-6 was required for Tc17 differentiation and immunity, but IL-1R1 and Dectin-1 signaling was unexpectedly dispensable. Tc17 cells expressed surface CXCR3 and CCR6, but only the latter was essential in recruitment to the lung. Although IL-17 producing T cells are believed to be short-lived, effector Tc17 cells expressed low levels of KLRG1 and high levels of the transcription factor TCF-1, predicting their long-term survival and stem-cell like behavior. Our work has implications for designing vaccines against fungal infections in immune suppressed patients.

Systemic fungal infections have emerged as a public health problem, especially for patients with suppressed immunity. At present, there are no vaccines against fungi, partly because it is hard to elicit strong immunity in immune suppressed patients. We have found however that residual elements of T cell immunity can be harnessed by vaccination even in immune suppressed hosts. We show here that immune suppressed mice lacking T helper cells can still be vaccinated successfully against lethal fungal pneumonia. A population of T cytotoxic IL-17-producing cells (Tc17 cells) is instrumental and indispensible in vaccine protection. We describe here mechanisms that explain how these cells are induced to mature in Tc17 cells, persist for long periods in the body providing “immune memory”, recruit to the site of infection, and clear the tissue of fungi. Our work sheds new light on potent T cells that can be harnessed by vaccine strategies against fungal infection in vulnerable patients.

Engineered T cells for anti-cancer therapy

Recent advances enabling efficient delivery of transgenes to human T cells have created opportunities to address obstacles that previously hindered the application of T cell therapy to cancer. Modification of T cells with transgenes encoding TCRs or chimeric antigen receptors allows tumor specificity to be conferred on functionally distinct T cell subsets, and incorporation of costimulatory molecules or cytokines can enable engineered T cells to bypass local and systemic tolerance mechanisms. Clinical studies of genetically modified T cell therapy for cancer have shown notable success; however, these trials demonstrate that tumor therapy with engineered high avidity tumor-reactive T cells may be accompanied by significant on-target toxicity, necessitating careful selection of target antigens and development of strategies to eliminate transferred cells.

On the perils of poor editing: regulation of peptide loading by HLA-DQ and H2-A molecules associated with celiac disease and type 1 diabetes

This review discusses mechanisms that link allelic variants of major histocompatibility complex (MHC) class II molecules (MHCII) to immune pathology. We focus on HLA (human leukocyte antigen)-DQ (DQ) alleles associated with celiac disease (CD) and type 1 diabetes (T1D) and the role of the murine DQ-like allele, H2-Ag7 (I-Ag7 or Ag7), in murine T1D. MHCII molecules bind peptides, and alleles vary in their peptide-binding specificity. Disease-associated alleles permit binding of disease-inducing peptides, such as gluten-derived, Glu-/Pro-rich gliadin peptides in CD and peptides from islet autoantigens, including insulin, in T1D. In addition, the CD-associated DQ2.5 and DQ8 alleles are unusual in their interactions with factors that regulate their peptide loading, invariant chain (Ii) and HLA-DM (DM). The same alleles, as well as other T1D DQ risk alleles (and Ag7), share nonpolar residues in place of Asp at β57 and prefer peptides that place acidic side chains in a pocket in the MHCII groove (P9). Antigen-presenting cells from T1D-susceptible mice and humans retain CLIP because of poor DM editing, although underlying mechanisms differ between species. We propose that these effects on peptide presentation make key contributions to CD and T1D pathogenesis.

Impact of culture medium on maturation of bone marrow-derived murine dendritic cells via the aryl hydrocarbon receptor

The aryl hydrocarbon receptor (AhR) plays a role in modulating dendritic cell (DC) immunity. Iscove's modified Dulbecco's medium (IMDM) contains higher amounts of AhR ligands than RPMI1640 medium. Here, we examined the influence of AhR ligand-containing medium on the maturation and T-cell stimulatory capacity of bone marrow-derived murine dendritic cells (BMDCs). BMDCs generated in IMDM (BMDCs/IMDM) expressed higher levels of co-stimulatory and MHC class II molecules, and lower levels of pattern-recognition receptors, especially toll-like receptor (TLR) 2, TLR4, and scavenger receptor class A (SR-A), compared to BMDCs generated in RPMI1640 medium (BMDCs/RPMI). Cytokine responses against ligands of TLRs and antigen uptake mediated by SR-A were remarkably reduced in BMDCs/IMDM, whereas the T-cell stimulatory capacity of the cells was enhanced, compared to BMDCs/RPMI. The enhanced maturation of BMDCs/IMDM was attenuated in the presence of an AhR antagonist, indicating involvement of AhR in the maturation. Interestingly, BMDCs/IMDM induced Th2 and Th17 differentiation at low and high concentrations of antigen respectively, when co-cultured with CD4(+) T-cells from antigen-specific T-cell receptor transgenic mice. In contrast, BMDCs/RPMI induced Th1 differentiation predominantly in the co-culture. Taken together, optimal selection of medium seems necessary when studying BMDCs, depending on the target receptors on the cell surface of DCs and type of helper T-cells for the co-culture.

The immune enhancement of a novel soy lecithin/β-glucans based adjuvant on native Neospora caninum tachyzoite extract vaccine in mice

Efficient, cost-effective and safe Th1-immunity-inducing vaccine formulations are paramount for achieving protection against Neospora caninum. In this study, a new adjuvant (Providean-AVEC) was used in the development of a N. caninum vaccine and evaluated in a mouse model. Soluble N. caninum tachyzoite native protein extract (sNcAg) was selected as vaccine antigen based on its capacity to activate production of pro-inflammatory cytokines on dendritic cells. Vaccines containing 4 and 0.4 μg of sNcAg, and Providean-AVEC, ISCOM-Matrix or aluminum hydroxide (Alum) were tested in BALB/c mice. While mice vaccinated with 4μg of sNcAg + Providean-AVEC developed specific antibodies shortly after the first dose, the rest of the high antigen payload formulations only induced seroconversion after the booster. Mice immunized with the high payload ISCOM vaccine (4 μg sNcAg) or with either low or high payload Providean-AVEC formulations (0.4 μg and 4 μg sNcAg, respectively) elicited higher IgG2a than IgG1 serum levels, and IFN-γ anamnestic responses with a Th1-cytokine biased profile. These animals had no histological signs of cerebral lesions and parasite burden assessed by quantitative real-time PCR was not detected. Vaccine preparations including Providean-AVEC as adjuvant limited N. canimum multiplication even with only a tenth of antigen payload compared to vaccines containing other adjuvants. Using adjuvants to specifically activate dendritic cells, combined with a careful antigen selection can enhance cellular responses to inert N. caninum vaccines.

TEC and MAPK Kinase Signalling Pathways in T helper (TH) cell Development, TH2 Differentiation and Allergic Asthma

Significant advances in our understanding of the signalling events during T cell development and differentiation have been made in the past few decades. It is clear that ligation of the T cell receptor (TCR) triggers a series of proximal signalling cascades regulated by an array of protein kinases. These orchestrated and highly regulated series of events, with differential requirements of particular kinases, highlight the disparities between αβ+CD4+ T cells. Throughout this review we summarise both new and old studies, highlighting the role of Tec and MAPK in T cell development and differentiation with particular focus on T helper 2 (TH2) cells. Finally, as the allergy epidemic continues, we feature the role played by TH2 cells in the development of allergy and provide a brief update on promising kinase inhibitors that have been tested in vitro, in pre-clinical disease models in vivo and into clinical studies.

Th17 cells are long lived and retain a stem cell-like molecular signature

Th17 cells have been described as short lived, but this view is at odds with their capacity to trigger protracted damage to normal and transformed tissues. We report that Th17 cells, despite displaying low expression of CD27 and other phenotypic markers of terminal differentiation, efficiently eradicated tumors and caused autoimmunity, were long lived, and maintained a core molecular signature resembling early memory CD8(+) cells with stem cell-like properties. In addition, we found that Th17 cells had high expression of Tcf7, a direct target of the Wnt and β-catenin signaling axis, and accumulated β-catenin, a feature observed in stem cells. In vivo, Th17 cells gave rise to Th1-like effector cell progeny and also self-renewed and persisted as IL-17A-secreting cells. Multipotency was required for Th17 cell-mediated tumor eradication because effector cells deficient in IFN-γ or IL-17A had impaired activity. Thus, Th17 cells are not always short lived and are a less-differentiated subset capable of superior persistence and functionality.

Human T cell cytokine responses are dependent on multidrug resistance protein-1

Multidrug resistance protein-1 (MRP1) belongs to subfamily C of the ATP-binding cassette transporters, and exports leukotriene C(4) and organic anions including the fluorescent calcium indicator indo-1. The observation that leukocytes from patients with an autoimmune disease exported indo-1 at a higher rate than controls prompted the hypothesis that MRP1 contributes to the function of activated cells. To test this, we defined the expression of MRP1 on resting and activated human T cells, and determined whether T cell activation is dependent upon MRP1 function. MRP1 is expressed on resting memory but not on naive CD4 and CD8 T cells. After activation through the TCR, cord blood CD4 T cells express high levels of MRP1. Blockade of MRP1 with the specific inhibitor MK-571 abrogated superantigen-induced expression of IFN-gamma, tumor necrosis factor-alpha, IL-10, IL-2, IL-4 and CD69 by T cells without affecting their viability, and was reversible upon removal of MK-571 from the culture media. Electrophoretic mobility shift assays demonstrate that MRP1 blockade with MK-571 induces activation of the transcriptional repressor peroxisome proliferator-activated receptor-gamma in CD4 T cells, thus providing insight into the potential mechanism by which their responses are abrogated.