Regulation and function of IL-17A- and IL-22-producing γδ T cells

The regulation of IL-17A and IL-22 production differs between human and murine γδ T cells. We find that human γδ T cells expressing Vγ2Vδ2 T cell receptors are peripherally polarized to produce IL-17A or IL-22, much like CD4 αβ Th17 T cells. This requires IL-6, IL-1β, and TGF-β, whereas expansion and maintenance requires IL-23, IL-1β, and TGF-β. In contrast, IL-17A and IL-22 production by murine γδ T cells is innately programmed during thymic ontogeny but requires IL-23 and IL-1β for maintenance. Murine γδ cells producing IL-17A and IL-22 play important roles in microbial, autoimmune, and inflammatory responses. However, the roles played by human IL-17A- and IL-22-producing γδ T cells are less clear but are also likely to be important. These observations highlight differences between humans and murine γδ T cells and underscore the importance of IL-17A- and IL-22-producing γδ T cells.     

The unique features of follicular T cell subsets

The germinal center (GC) reaction is critical for humoral immunity, but also contributes adversely to a variety of autoimmune diseases. While the major protective function of GCs is mediated by plasma cells and memory B cells, follicular helper T (TFH) cells represent a specialized T cell subset that provides essential help to the antigen-specific B cells in the form of membrane-bound ligands and secreted factors such as IL-21. Recent studies have revealed that TFH cells are capable of considerable functional diversity as well as possessing the ability to form memory cells. The molecular basis of this plasticity and heterogeneity is only now emerging. It has also become apparent that several other populations of follicular T cells exist, including natural killer T cells and regulatory T cells. In this review we will discuss the function of follicular T cells and interaction of these populations within the GC response.     

<Emphasis Type="Italic">Yersinia pseudotuberculosis</Emphasis> supports Th17 differentiation and limits de novo regulatory T cell induction by directly interfering with T cell receptor signaling

Adaptive immunity critically contributes to control acute infection with enteropathogenic Yersinia pseudotuberculosis; however, the role of CD4⁺ T cell subsets in establishing infection and allowing pathogen persistence remains elusive. Here, we assessed the modulatory capacity of Y. pseudotuberculosis on CD4⁺ T cell differentiation. Using in vivo assays, we report that infection with Y. pseudotuberculosis resulted in enhanced priming of IL-17-producing T cells (Th17 cells), whereas induction of Foxp3⁺ regulatory T cells (Tregs) was severely disrupted in gut-draining mesenteric lymph nodes (mLNs), in line with altered frequencies of tolerogenic and proinflammatory dendritic cell (DC) subsets within mLNs. Additionally, by using a DC-free in vitro system, we could demonstrate that Y. pseudotuberculosis can directly modulate T cell receptor (TCR) downstream signaling within naïve CD4⁺ T cells and Tregs via injection of effector molecules through the type III secretion system, thereby affecting their functional properties. Importantly, modulation of naïve CD4⁺ T cells by Y. pseudotuberculosis resulted in an enhanced Th17 differentiation and decreased induction of Foxp3⁺ Tregs in vitro. These findings shed light to the adjustment of the Th17-Treg axis in response to acute Y. pseudotuberculosis infection and highlight the direct modulation of CD4⁺ T cell subsets by altering their TCR downstream signaling.     

T helper 17 cells: discovery, function, and physiological trigger

In the few years since their discovery, T helper 17 cells (T_H17) have been shown to play an important role in host defense against infections, and in tissue inflammation during autoimmunity. T_H17 cells produce IL-17, IL-21, IL-10, and IL-22 cytokines, and thus have broad effects on a variety of tissues. Notably, the requirement for the immunosuppressive cytokine TGF-β along with the pro-inflammatory cytokine IL-6 for T_H17 differentiation supports the intimate relationship between the T_H17 subset and FOXP3⁺ regulatory T cells. Here, we discuss current knowledge on effector functions and differentiation of the T_H17 lineage. Furthermore, we now know of a physiological stimulus for T_H17 differentiation: innate immune recognition of cells undergoing apoptosis as a direct result of infection induces unique development of this subset. As our knowledge of T_H17 and T regulatory cells grows, we are building on a new framework for the understanding of effector T cell differentiation and the biology of CD4⁺ T cell adaptive immune responses.     

Interleukin-17 stimulates inducible nitric oxide synthase-dependent toxicity in mouse beta cells

The influence of the proinflammatory cytokine interleukin (IL)-17 on inducible nitric oxide (NO) synthase (iNOS)-mediated NO release was investigated in the mouse insulinoma cell line MIN6 and mouse pancreatic islets. IL-17 markedly augmented iNOS mRNA/protein expression and subsequent NO production induced in MIN6 cells or pancreatic islets by different combinations of interferon-γ, tumor necrosis factor-α, and IL-1β. The induction of iNOS by IL-17 was preceded by phosphorylation of p38 mitogen-activated protein kinase (MAPK), and inhibition of p38 MAPK activation completely abolished IL-17-stimulated NO release. IL-17 enhanced the NO-dependent toxicity of proinflammatory cytokines toward MIN6 cells, while IL-17-specific neutralizing antibody partially reduced the NO production and rescued insulinoma cells and pancreatic islets from NO-dependent damage induced by activated T cells. Finally, a significant increase in blood IL-17 levels was observed in a multiple low-dose streptozotocin model of diabetes, suggesting that T cell-derived IL-17 might be involved in NO-dependent damage of beta cells in this disease. Received 14 June 2005; received after revision 17 September 2005; accepted 21 September 2005     

Roles for interleukin-2 (IL-2) and IL-4 in the generation of allocytotoxic T cells in the primary and secondary responses in vitro.

Roles for interleukin-2 (IL-2) and IL-4 in the generation of murine allocytotoxine T lymphocytes (allo-CTL) in the primary and secondary responses were studied in vitro. The generation of allo-CTL in the primary response was inhibited by anti-IL-2 monoclonal antibody (mAb), but was not inhibited by anti-IL-4 mAb. On the other hand, the generation of allo-CTL in the secondary response was partially inhibited by either anti-IL-2 or anti-IL-4 mAb, and it was almost completely inhibited by the combination of two mAbs. CD8+ cell-depleted splenocytes produced IL-2, but not IL-4, in response to alloantigens in the primary response, and these cells produced both IL-2 and IL-4 in the secondary response. Both exogenous IL-2 and IL-4 induced functionally active allo-CTL in the primary response from CD4+ cell-depleted splenocytes when these cells were stimulated with T cell-depleted allogeneic cells. These results suggest that the allo-CTL induction in the primary response is IL:-2-dependent and secondary allo-CTL induction is both IL-2 and IL-4-dependent, because unprimed CD4+ T cells produce IL-2, but not IL-4, whereas primed cells produce both IL-2 and IL-4 in response to alloantigens.     

Interleukin-17: a mediator of inflammatory responses

Interleukin-17 (IL-17) is a prototype member of a new cytokine family with six species identified to date. IL-17 is secreted mainly by activated CD4⁺ and CD8⁺ T lymphocytes, while its receptor is distributed ubiquitously. IL-17 has been classified as a proinflammatory cytokine because of its ability to induce the expression of many mediators of inflammation, most strikingly those that are involved in the proliferation, maturation and chemotaxis of neutrophils. Increased levels of IL-17 have been associated with several conditions, including airway inflammation, rheumatoid arthritis, intraperitoneal abscesses and adhesions, inflammatory bowel disease, allograft rejection, psoriasis, cancer and multiple sclerosis. This review provides an overview of IL-17 activities, concentrating on those that lead to neutrophil recruitment.Received 13 June 2003; received after revision 27 August 2003; accepted 1 September 2003     

2-Carboxyethylgermanium sesquioxide,a synthetic organogermanium compound,as an inducer of contrasuppressor T cells

2-Carboxyethylgermanium sesquioxide (Ge-132), a synthesized organogermanium compound with immunomodulaing activities, was shown to be an inducer of anti-suppressor T cells in normal mice. The suppressor cell activity of T6S cells, a clone of burn-induced CD8⁺ IL-4-producing suppressor T cells, was clearly inhibited when a mixed lymphocyte-tumor cell reaction of the clone was conducted with splenic mononuclear cells from mice treated orally with a 100 mg/kg dose of Ge-132. The activity of anti-suppressor cells was demonstrated in spleens of mice 2 days after treatment with Ge-132 and reached its peak on day 3. The anti-suppressor cells induced by the compound were of a contrasuppressor T cell-linage, because they were characterized as CD4⁺ CD28⁺ TCR/⁺ Vicia villosa lectin-adherent T cells. These cells produced IFN- but did not produce IL-2, IL-4, IL-6 or IL-10 in their culture fluids. CD4⁺ anti-suppressor T cells induced by Ge-132 may be different from other subsets of CD4⁺ T cells because Th1 and Th2 cells generated in our laboratory did not adhere toVicia villosa lectin-coated petri dishes, and each produced specific cytokines. Th1 cells produced IFN- and IL-2 while Th2 cells produce IL-4 and IL-10 in vitro. These results suggest that Ge-132 may be useful as an inducer of contrasuppressor T cells in immunocompromised individuals bearing suppressor T cells. To eliminate suppressor T cells from immunocompromised hosts may result in improved resistance from various opportunistic infections.     

Valproic acid attenuates inflammation in experimental autoimmune neuritis

Valproic acid (VPA) is a short-chain branched fatty with anti-inflammatory, neuro-protective and axon-remodeling effects. We investigated the effects of VPA in rats in which experimental autoimmune neuritis (EAN) had been induced (EAN rats). VPA (300 mg/kg, intraperitoneally) administration to EAN rats once daily immediately following immunization significantly suppressed mRNA levels of interferon-γ, tumor necrosis factor-α, interleukin (IL)-1β, IL-4, IL-6 and IL-17 in the lymph nodes of EAN rats. In peripheral blood and sciatic nerves of EAN rats, Foxp3⁺ cells were increased but IL-17⁺ cells were decreased during VPA treatment. Furthermore, suppressive and therapeutic treatment with VPA greatly attenuated both accumulation of macrophages, T cells and B cells, and demyelination in sciatic nerves, and greatly reduced the severity and duration of EAN. In summary, our data demonstrated that VPA could effectively suppress inflammation in EAN, suggesting that VPA could be a potent candidate for treatment of autoimmune neuropathies.     

Generation of cellular immune responses to antigenic tumor peptides

Tumor immunotherapy is currently receiving close scrutiny. However, with the identification of tumor antigens and their production by recombinant means, the use of cytokines and knowledge of major histocompatibility complex (MHC) class I and class II presentation has provided ample reagents for use and clear indications of how they should be used. At this time, much attention is focused on using peptides to be presented by MHC class I molecules to both induce and be targets for CD8+ cytolytic T cells. Many peptides generated endogenously or given exogenously can enter the class I pathway, but a number of other methods of entering this pathway are also known and are discussed in detail herein. While the review concentrates on inducing cytotoxic T cells (CTLs), it is becoming increasingly apparent that other modes of immunotherapy would be desirable, such as class II presentation to induce increased helper activity (for CTL), but also activating macrophages to be effective against tumor cells.     

Homeostatic maintenance of T cells and natural killer cells

Homeostasis in the immune system encompasses the mechanisms governing maintenance of a functional and diverse pool of lymphocytes, thus guaranteeing immunity to pathogens while remaining self-tolerant. Antigen-naïve T cells rely on survival signals through contact with self-peptide-loaded major histocompatibility complex (MHC) molecules plus interleukin (IL)-7. Conversely, antigen-experienced (memory) T cells are typically MHC-independent and they survive and undergo periodic homeostatic proliferation through contact with both IL-7 and IL-15. Also, non-conventional γδ T cells rely on a mix of IL-7 and IL-15 for their homeostasis, whereas natural killer cells are mainly dependent on contact with IL-15. Homeostasis of CD4⁺ T regulatory cells is different in being chiefly regulated by contact with IL-2. Notably, increased levels of these cytokines cause expansion of responsive lymphocytes, such as found in lymphopenic hosts or following cytokine injection, whereas reduced cytokine levels cause a decline in cell numbers.     

High frequency of human cytomegalovirus (HCMV)-specific CD8+-T cells detected in a healthy CMV-seropositive donor

Human cytomegalovirus (HCMV) persists after infection but is controlled by cellular immune responses, particularly by CD8⁺ T cells. If infected individuals are immunosuppressed, HCMV can be reactivated. Upon testing the blood of healthy donors with human lymphocyte antigen tetramers, we found one individual with about 50 % of his CD8⁺ T cells being specific for the immunodominant pp65 epitope NLVPMVATV. Over a period of 2 years the high level of HCMV-specific T cells was maintained, and no HCMV DNA could be detected. At one timepoint, however, HCMV-specific DNA was detected, while 65 % of CD8⁺ T cells were specific for HCMV. When virus was detectable, a lower percentage of HCMV-specific CD8⁺ T cells showed interferon γ (IFN-γ) production after peptide stimulation in vitro. These data suggest that HCMV reactivation may also occur in immunocompetent persons, accompanied by the presence of HCMV-specific CD8⁺ T cells which are not producing IFNγ, and therefore potentially anergic or in vivo exhausted. Received 6 March 2002; received after revision 15 April 2002; accepted 17 April 2002     

The biology of cell locomotion within three-dimensional extracellular matrix

Cell migration in three-dimensional (3-D) extracellular matrix (ECM) is not a uniform event but rather comprises a modular spectrum of interdependent biophysical and biochemical cell functions. Haptokinetic cell migration across two-dimensional (2-D) surfaces consists of at least three processes: (i) the protrusion of the leading edge for adhesive cell-substratum interactions is followed by (ii) contraction of the cell body and (iii) detachment of the trailing edge. In cells of flattened morphology migrating slowly across 2-D substrate, contact-dependent clustering of adhesion receptors including integrins results in focal contact and stress fiber formation. While haptokinetic migration is predominantly a function of adhesion and deadhesion events lacking spatial barriers towards the advancing cell body, the biophysics of the tissues require a set of cellular strategies to overcome matrix resistance. Matrix barriers force the cells to adapt their morphology and change shape and/or enzymatically degrade ECM components, either by contact-dependent proteolysis or by protease secretion. In 3-D ECM, in contrast to 2-D substrate, the cell shape is mostly bipolar and the cytoskeletal organization is less stringent, frequently lacking discrete focal contacts and stress fibers. Morphologically large spindle-shaped cells (i.e., fibroblasts, endothelial cells, and many tumor cells) of high integrin expression and strong cytoskeletal contractility utilize integrin-dependent migration strategies that are coupled to the capacity to reorganize ECM. In contrast, a more dynamic ameboid migration type employed by smaller cells expressing low levels of integrins (i.e., T lymphocytes, dendritic cells, some tumor cells) is characterized by largely integrin-independent interaction strategies and flexible morphological adaptation to preformed fiber strands, without structurally changing matrix architecture. In tumor invasion and angiogenesis, migration mechanisms further comprise the migration of entire cell clusters or strands maintaining stringent cell-cell adhesion and communication while migrating. Lastly, cellular interactions, enzyme and cytokine secretion, and tissue remodeling provided by reactive stroma cells (i.e. fibroblasts and macrophages) contribute to cell migration. In conclusion, depending on the cellular composition and tissue context of migration, diverse cellular and molecular migration strategies can be developed by different cell types.     

Blockage of the NLRP3 inflammasome by MCC950 improves anti-tumor immune responses in head and neck squamous cell carcinoma

The NLRP3 inflammasome is a critical innate immune pathway responsible for producing active interleukin (IL)-1β, which is associated with tumor development and immunity. However, the mechanisms regulating the inflammatory microenvironment, tumorigenesis and tumor immunity are unclear. Herein, we show that the NLRP3 inflammasome was over-expressed in human HNSCC tissues and that the IL-1β concentration was increased in the peripheral blood of HNSCC patients. Additionally, elevated NLRP3 inflammasome levels were detected in tumor tissues of Tgfbr1/Pten 2cKO HNSCC mice, and elevated IL-1β levels were detected in the peripheral blood serum, spleen, draining lymph nodes and tumor tissues. Blocking NLRP3 inflammasome activation using MCC950 remarkably reduced IL-1β production in an HNSCC mouse model and reduced the numbers of myeloid-derived suppressor cells (MDSCs), regulatory T cells (Tregs) and tumor-associated macrophages (TAMs). Moreover, inhibiting NLRP3 inflammasome activation increased the numbers of CD4⁺ and CD8⁺ T cells in HNSCC mice. Notably, the numbers of exhausted PD-1⁺ and Tim3⁺ T cells were significantly reduced. A human HNSCC tissue microarray showed that NLRP3 inflammasome expression was correlated with the expression of CD8 and CD4, the Treg marker Foxp3, the MDSC markers CD11b and CD33, and the TAM markers CD68 and CD163, PD-1 and Tim3. Overall, our results demonstrate that the NLRP3 inflammasome/IL-1β pathway promotes tumorigenesis in HNSCC and inactivation of this pathway delays tumor growth, accompanied by decreased immunosuppressive cell accumulation and an increased number of effector T cells. Thus, inhibition of the tumor microenvironment through the NLRP3 inflammasome/IL-1β pathway may provide a novel approach for HNSCC therapy.     

MAIT cells and pathogen defense

Mucosa-associated invariant T (MAIT) cells are a unique population of innate T cells that are abundant in humans. These cells possess an evolutionarily conserved invariant T cell receptor α chain restricted by the nonpolymorphic class Ib major histocompatibility (MHC) molecule, MHC class I-related protein (MR1). The recent discovery that MAIT cells are activated by MR1-bound riboflavin metabolite derivatives distinguishes MAIT cells from all other αβ T cells in the immune system. Since mammals lack the capacity to synthesize riboflavin, intermediates from the riboflavin biosynthetic pathway are distinct microbial molecular patterns that provide a unique signal to the immune system. Multiple lines of evidence suggest that MAIT cells, which produce important cytokines such as IFN-γ, TNF, and IL-17A, have the potential to influence immune responses to a broad range of pathogens. Here we will discuss our current understanding of MAIT cell biology and their role in pathogen defense.     

Protein folding and degradation in bacteria: to degrade or not to degrade? That is the question

In Escherichia coli protein quality control is carried out by a protein network, comprising chaperones and proteases. Central to this network are two protein families, the AAA+ and the Hsp70 family. The major Hsp70 chaperone, DnaK, efficiently prevents protein aggregation and supports the refolding of damaged proteins. In a special case, DnaK, together with the assistance of the AAA+ protein ClpB, can also refold aggregated proteins. Other Hsp70 systems have more specialized functions in the cell, for instance HscA appears to be involved in the assembly of Fe/S proteins. In contrast to ClpB, many AAA+ proteins associate with a peptidase to form proteolytic machines which remove irreversibly damaged proteins from the cellular pool. The AAA+ component of these proteolytic machines drives protein degradation. They are required not only for recognition of the substrate but also for substrate unfolding and translocation into the proteolytic chamber. In many cases, specific adaptor proteins modify the substrate binding properties of AAA+ proteins. While chaperones and proteases do not appear to directly cooperate with each other, both systems appear to be necessary for proper functioning of the cell and can, at least in part, substitute for one another. RID="*" ID="*"Corresponding author.     

Roles for interleukin-2 (IL-2) and IL-4 in the generation of allocytotoxic T cells in the primary and secondary responses in vitro

Roles for interleukin-2(IL-2) and IL-4 in the generation of murine allocytotoxine T lymphocytes (allo-CTL) in the primary and secondary responses were studied in vitro. The generation of allo-CTL in the primary response was inhibited by anti-IL-2 monoclonal antibody (mAb), but was not inhibited by anti-IL-4 mAb. On the other hand, the generation of allo-CTL in the secondary response was partially inhibited by either anti-IL-2 or anti-IL-4 mAb, and it was almost completely inhibited by the combination of two mAbs. CD8⁺ cell-depleted splenocytes produced IL-2, but not IL-4, in response to alloantigens in the primary response, and these cells produced both IL-2 and IL-4 in the secondary response. Both exogenous IL-2 and IL-4 induced functionally active allo-CTL in the primary response from CD4⁺ cell-depleted splenocytes when these cells were stimulated with T cell-depleted allogeneic cells. These results suggest that the allo-CTL induction in the primary response is IL:-2-dependent and secondary allo-CTL induction is both IL-2 and IL-4-dependent, because unprimed CD4⁺ T cells produce IL-2, but not IL-4, whereas primed cells produce both IL-2 and IL-4 in response to alloantigens.