CTLA‐4 (CD152) enhances the Tc17 differentiation program

Although CD8⁺ T cells that produce IL‐17 (Tc17 cells) have been linked to host defense, Tc17 cells show reduced cytotoxic activity, which is the characteristic function of CD8⁺ T cells. Here, we show that CTLA‐4 enhances the frequency of IL‐17 in CD8⁺ T cells, indicating that CTLA‐4 (CD152) specifically promotes Tc17 differentiation. Simultaneous stimulation of CTLA‐4^+/+ and CTLA‐4^?/? T cells in cocultures and agonistic CTLA‐4 stimulation unambiguously revealed a cell‐intrinsic mechanism for IL‐17 control by CTLA‐4. The quality of CTLA‐4‐induced Tc17 cells was tested in vivo, utilizing infection with the facultative intracellular bacterium Listeria monocytogenes (LM). Unlike CTLA‐4^+/+ Tc17 cells, CTLA‐4^?/? were nearly as efficient as Tc1 CTLA‐4^+/+ cells in LM clearance. Additionally, adoptively transferred CTLA‐4^?/? Tc17 cells expressed granzyme B after rechallenge, and produced Tc1 cytokines such as IFN‐γ and TNF‐α, which strongly correlate with bacterial clearance. CTLA‐4^+/+ Tc17 cells demonstrated a high‐quality Tc17 differentiation program ex vivo, which was also evident in isolated IL‐17‐secreting Tc17 cells, with CTLA‐4‐mediated enhanced upregulation of Tc17‐related molecules such as IL‐17A, RORγt, and IRF‐4. Our results show that CTLA‐4 promotes Tc17 differentiation that results in robust Tc17 responses. Its inactivation might therefore represent a central therapeutic target to enhance clearance of infection.     

The proportion of different interleukin‐17‐producing T‐cell subsets is associated with liver fibrosis in chronic hepatitis C

Studies have suggested the pivotal role of T helper type 1 (Th1) ‐related cytokines on the outcome of hepatitis C virus (HCV) infection. Nevertheless, the role of different interleukin‐17 (IL‐17) ‐secreting T cells on chronic hepatitis C (CHC) is less clear. Here, the in vivo IL‐1β, IL‐6, and IL‐17 levels were positively correlated with both alanine transaminase (ALT) levels and hepatic lesions. When compared with the control group, CHC patients showed a lower proportion of IL‐17‐secreting (CD4⁺ and CD8⁺) T cells capable of simultaneously producing IL‐21. Moreover, the percentage of IL‐10‐secreting Th17 cells was also lower in CHC patients. Notably, advanced liver lesions were observed among those patients with lower percentage levels of IL‐17‐producing T cells positive for IL‐21, interferon‐γ (IFN‐γ) and IL‐10. In contrast, the severity of hepatic damage was associated with peripheral single IL‐17⁺ T cells. The percentage of IL‐17⁺ IL‐21^– IFN‐γ⁺ (CD4⁺ and CD8⁺) T‐cell phenotypes was positively associated with plasma CD14 levels. Finally, elevated levels of circulating CD14 were detected among CHC patients with extensive liver damage. In summary, although preliminary, our results suggest that a balance between different IL‐17‐producing T cells, associated with peripheral levels of CD14, may be a progress marker for liver disease in chronically HCV‐infected patients.     

Committed Tc17 cells are phenotypically and functionally resistant to the effects of IL‐27

IL‐17‐secreting CD8⁺ T cells (Tc17 cells) have been implicated in immunity to infections, cancer, and autoimmune diseases. Thus far, studies on Tc17 cells have primarily investigated their development from naïve precursors, while the biology of committed Tc17 cells has been less characterized, in particular during the effector phase of immune responses. IL‐27 is an important regulator of inflammation through the induction of regulatory Tr1 cells, as well as a suppressor of Th17‐cell development. IL‐27 suppresses the development of Tc17 cells, but its effects on committed Tc17 cells are unknown. Here we demonstrate that even though IL‐27 completely inhibited the development of C57BL/6 mouse Tc17 cells, it had little effect on previously committed Tc17 cells. Although committed Tc17 cells were capable of responding to IL‐27, it had no effect on expression of RORγt and RORα, or production of various cytokines. Committed Tc17 cells did not express granzyme B and lacked cytotoxicity in vitro, features that remained unaltered by IL‐27 treatment. Nonetheless, they efficiently induced diabetes, irrespective of treatment with IL‐27 prior to transfer into RIP‐mOVA mice. These findings suggest that use of IL‐27 to modulate autoimmune diseases might have limited therapeutic efficacy if autoaggressive Tc17 cells have already developed.     

MicroRNA‐155 may be involved in the pathogenesis of atopic dermatitis by modulating the differentiation and function of T helper type 17 (Th17) cells

Our aims were to identify the differential expression of microRNA (miR)‐155, as well as to explore the possible regulatory effects of miR‐155 on the differentiation and function of T helper type 17 (Th17) cells in atopic dermatitis (AD). The Th17 cell percentage and expression levels of miR‐155, retinoic acid‐related orphan receptor (ROR)γt, interleukin (IL)‐17 and suppressor of cytokine signalling‐1 (SOCS1) in peripheral CD4⁺ T cells, plasma and skin specimens were detected and compared in AD patients and healthy subjects. A miR‐155 mimic and an inhibitor were transfected separately into AD CD4⁺ T cells to confirm the in‐vivo data. The Th17 cell percentage, miR‐155 expression, RORγt mRNA expression, IL‐17 mRNA expression and plasma concentration were increased significantly in AD patients compared with healthy subjects. Conversely, SOCS1 mRNA expression and plasma concentration were decreased significantly. Similar results were detected in cultured CD4⁺ T cells transfected with the miR‐155 mimic compared with a miR‐155 inhibitor or a negative control. Additionally, there was a sequential decrease in miR‐155 expression, as well as RORγt and IL‐17 mRNA expression, but an increase in SOCS1 mRNA expression, from AD lesional skin and perilesional skin to normal skin. Positive correlations were found between miR‐155 expression and AD severity, Th17 cell percentage, RORγt mRNA expression and IL‐17 mRNA expression and plasma concentration, while negative correlations were observed between miR‐155 expression and SOCS1 mRNA expression and plasma concentration in AD peripheral circulation and skin lesions. In conclusion, miR‐155 is over‐expressed and may be involved in AD pathogenesis by modulating the differentiation and function of Th17 cells.     

TGF‐β indirectly favors the development of human Th17 cells by inhibiting Th1 cells

Human Th17 clones and circulating Th17 cells showed lower susceptibility to the anti‐proliferative effect of TGF‐β than Th1 and Th2 clones or circulating Th1‐oriented T cells, respectively. Accordingly, human Th17 cells exhibited lower expression of clusterin, and higher Bcl‐2 expression and reduced apoptosis in the presence of TGF‐β, in comparison with Th1 cells. Umbilical cord blood naïve CD161⁺CD4⁺ T cells, which contain the precursors of human Th17 cells, differentiated into IL‐17A‐producing cells only in response to IL‐1β plus IL‐23, even in serum‐free cultures. TGF‐β had no effect on constitutive RORγt expression by umbilical cord blood CD161⁺ T cells but it increased the relative proportions of CD161⁺ T cells differentiating into Th17 cells in response to IL‐1β plus IL‐23, whereas under the same conditions it inhibited both T‐bet expression and Th1 development. These data suggest that TGF‐β is not critical for the differentiation of human Th17 cells, but indirectly favors their expansion because Th17 cells are poorly susceptible to its suppressive effects.     

Different interleukin‐17‐secreting Toll‐like receptor+ T‐cell subsets are associated with disease activity in multiple sclerosis

Signalling through Toll‐like receptors (TLRs) may play a role in the pathogenesis of autoimmune diseases, such as multiple sclerosis (MS). In the present study, the expression of TLR‐2, ‐4 and ‐9 was significantly higher on CD4⁺ and CD8⁺ T‐cells from MS patients compared to healthy individuals. Following in‐vitro activation, the proportion of interleukin (IL)‐17⁺ and IL‐6⁺ CD4⁺ and CD8⁺ T‐cells was higher in the patients. In addition, the proportion of IFN‐γ‐secreting TLR⁺ CD8⁺ T‐cells was increased in MS patients. Among different IL‐17⁺ T‐cell phenotypes, the proportion of IL‐17⁺ TLR⁺ CD4⁺ and CD8⁺ T‐cells producing IFN‐γ or IL‐6 were positively associated with the number of active brain lesions and neurological disabilities. Interestingly, activation of purified CD4⁺ and CD8⁺ T‐cells with ligands for TLR‐2 (Pam3Csk4), TLR‐4 [lipopolysaccharide (LPS)] and TLR‐9 [oligodeoxynucleotide (ODN)] directly induced cytokine production in MS patients. Among the pathogen‐associated molecular patterns (PAMPs), Pam3Csk4 was more potent than other TLR ligands in inducing the production of all proinflammatory cytokines. Furthermore, IL‐6, IFN‐γ, IL‐17 and granulocyte–macrophage colony‐stimulating factor (GM‐CSF) levels produced by Pam3Csk4‐activated CD4⁺ cells were directly associated with disease activity. A similar correlation was observed with regard to IL‐17 levels released by Pam3Csk4‐stimulated CD8⁺ T‐cells and clinical parameters. In conclusion, our data suggest that the expansion of different T helper type 17 (Th17) phenotypes expressing TLR‐2, ‐4 and ‐9 is associated with MS disease activity, and reveals a preferential ability of TLR‐2 ligand in directly inducing the production of cytokines related to brains lesions and neurological disabilities.     

T cell‐derived leptin contributes to increased frequency of T helper type 17 cells in female patients with Hashimoto's thyroiditis

Leptin modulates T cell function and plays an important role in autoimmune diseases. Our study aimed to explore the role of leptin and T helper type 17 (Th17) cells in Hashimoto's thyroiditis patients. Twenty‐seven patients with Hashimoto's thyroiditis (HT) and 20 healthy controls were enrolled into the current study. A modest increase of plasma leptin in HT patients and the CD4⁺ T cell‐derived leptin from HT patients was stronger than that from healthy controls. In HT patients, there are no statistically significant correlations between plasma leptin concentrations and the percentage of Th17 cells or the level of retinoic acid‐related orphan receptor γt (RORγt), but strong positive correlations were observed between CD4⁺ T cell‐derived leptin and the percentage of Th17 cells or the level of RORγt mRNA, and additionally significantly up‐regulated leptin, interleukin (IL)17 and RORγt mRNA levels in the thyroid tissue. Furthermore, neutralization of leptin decreases the frequency of Th17 cells in vitro. Current study has revealed an increased leptin involvment in Hashimoto's thyroiditis associated with an increased number of Th17 cells.     

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.     

CD8+ T cells producing IL‐3 and IL‐5 in non‐IgE‐mediated eosinophilic diseases

The cytokines IL‐5, IL‐3, and GM‐CSF are crucial for eosinophil development, survival, and function. To better understand their role in non‐IgE‐mediated eosinophilic diseases, we investigated plasma levels of these cytokines as well as cytokine expression in peripheral blood T cells. While we did not find any evidence for an involvement of T‐cell‐derived GM‐CSF, some of these patients did show an increased proportion of IL‐5‐ or IL‐3‐producing CD4⁺ T cells. However, in a significant proportion of patients, IL‐5‐producing CD8⁺ T cells, so‐called Tc2 cells, which in healthy donors can only be detected at very low levels, were prominent. Furthermore, increased IL‐3 production by CD8⁺ T cells was also observed, strongly supporting the notion that CD8⁺ T cells, not just CD4⁺ T cells, must also be considered as a potential source of the cytokines promoting eosinophilia.     

Genetic ablation of PI3Kγ results in defective IL‐17RA signalling in T lymphocytes and increased IL‐17 levels

The signalling molecule PI3Kγ has been reported to play a key role in the immune system and the inflammatory response. In particular, it facilitates the migration of haemato‐poietic cells to the site of inflammation. In this study, we reveal a novel role for PI3Kγ in the regulation of the pro‐inflammatory cytokine IL‐17. Loss of PI3Kγ or expression of a catalytically inactive mutant of PI3Kγ in mice led to increased IL‐17 production both in vitro and in vivo in response to various stimuli. The kinetic profile was unaltered from WT cells, with no effect on proliferation or other cytokines. Elevated levels of IL‐17 were not due to an aberrant expansion of IL‐17‐producing cells. Furthermore, we also identified an increase in IL‐17RA expression on PI3Kγ^?/? CD4⁺ T cells, yet these cells exhibited impaired PI3K‐dependent signalling in response to IL‐17A, and subsequent NF‐κB phosphorylation. In vivo, instillation of recombinant IL‐17 into the airways of mice lacking PI3Kγ signalling also resulted in reduced phosphorylation of Akt. Cell influx in response to IL‐17 was also reduced in PI3Kγ^?/? lungs. These data demonstrate PI3Kγ‐dependent signalling downstream of IL‐17RA, which plays a pivotal role in regulating IL‐17 production in T cells.