Mycobacterium tuberculosis PstS1 amplifies IFN‐γ and induces IL‐17/IL‐22 responses by unrelated memory CD4+ T cells via dendritic cell activation

The immunological mechanisms that modulate protection during Mycobacterium tuberculosis (Mtb) infection or vaccination are not fully understood. Secretion of IFN‐γ and, to a lesser extent, of IL‐17 by CD4⁺ T cells plays a major role both in protection and immunopathology. Few Mtb Ags interacting with DCs affect priming, activation, and regulation of Ag‐unrelated CD4⁺ T‐cell responses. Here we demonstrate that PstS1, a 38 kDa‐lipoprotein of Mtb, promotes Ag‐independent activation of memory T lymphocytes specific for Ag85B or Ag85A, two immunodominant protective Ags of Mtb. PstS1 expands CD4⁺ and CD8⁺ memory T cells, amplifies secretion of IFN‐γ and IL‐22 and induces IL‐17 production by effector memory cells in an Ag‐unrelated manner in vitro and in vivo. These effects were mediated through the stimulation of DCs, particularly of the CD8α^? subtype, which respond to PstS1 by undergoing phenotypic maturation and by secreting IL‐6, IL‐1β and, to a lower extent, IL‐23. IL‐6 secretion by PstS1‐stimulated DCs was required for IFN‐γ, and to a lesser extent for IL‐22 responses by Ag85B‐specific memory T cells. These results may open new perspectives for immunotherapeutic strategies to control Th1/Th17 immune responses in Mtb infections and in vaccinations against tuberculosis.     

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.     

Sympathetic neural signaling via the β2‐adrenergic receptor suppresses T‐cell receptor‐mediated human and mouse CD8+ T‐cell effector function

Postganglionic sympathetic neurons innervate secondary lymphoid organs and secrete norepinephrine (NE) as the primary neurotransmitter. NE binds and signals through five distinct members of the adrenergic receptor family. In this study, we show elevated expression of the β2‐adrenergic receptor (ADRB2) on primary human CD8⁺ effector memory T cells. Treatment of both human and murine CD8⁺ T cells with NE decreased IFN‐γ and TNF‐α secretion and suppressed their cytolytic capacity in response to T‐cell receptor (TCR) activation. The effects of NE were specifically reversed by β 2‐specific antagonists. Adrb2^?/? CD8⁺ T cells were completely resistant to the effects of NE. Further, the ADRB2‐specific pharmacological ligand, albuterol, significantly suppressed effector functions in both human and mouse CD8⁺ T cells. While both TCR activation and stimulation with IL‐12 + IL‐18 were able to induce inflammatory cytokine secretion, NE failed to suppress IFN‐γ secretion in response to IL‐12 + IL18. Finally, the long‐acting ADRB2‐specific agonist, salmeterol, markedly reduced the cytokine secretion capacity of CD8⁺ T cells in response to infection with vesicular stomatitis virus. This study reveals a novel intrinsic role for ADRB2 signaling in CD8⁺ T‐cell function and underscores the novel role this pathway plays in adaptive T‐cell responses to infection.     

Innate,antigen‐independent role for T cells in the activation of the immune system by Propionibacterium acnes

Propionibacterium acnes is a human commensal but also an opportunistic pathogen. In mice, P. acnes exerts strong immunomodulatory activities, including formation of intrahepatic granulomas and induction of LPS hypersensitivity. These activities are dependent on P. acnes recognition via TLR9 and subsequent IL‐12‐mediated IFN‐γ production. We show that P. acnes elicits IL‐12p40 and p35 mRNA expression in macrophages, and IFN‐γ mRNA in liver CD4⁺ T cells and NK cells. After priming with P. acnes, CD4⁺ T cells serve as the major IFN‐γ mRNA source. In the absence of CD4⁺ T cells, CD8⁺ T cells (regardless of antigenic specificity) or NK cells can produce sufficient IFN‐γ to induce the P. acnes‐driven immune effects. Moreover, in the absence of αβT cells, γδT cells also enable the development of strongly enhanced TNF‐α and IFN‐γ responses to LPS and intrahepatic granuloma formation. Thus, under microbial pressure, different T‐cell types, independent of their antigen specificity, exert NK‐cell‐like functions, which contribute decisively to the activation of the innate immune system.     

TLR8‐mediated activation of human monocytes inhibits TL1A expression

TLR play important roles in inflammation and innate immune response to pathogens. TLR8 recognizes ssRNA and induces NF‐κB via MyD88 signaling. TL1A is a member of the TNF superfamily that markedly enhances IFN‐γ production by IL‐12/IL‐18‐stimulated peripheral and mucosal CD4⁺ T cells. TL1A expression is increased in the mucosa of patients with inflammatory bowel disease and is considered a key mediator of Crohn's disease (CD). We have previously shown that TL1A is strongly induced by immune complexes (IC) but not TLR ligands in antigen‐presenting cells. However, a potential interaction between these pro‐inflammatory signaling pathways has not been investigated. IC‐induced TL1A expression of monocytes was potently inhibited by a TLR8 or TLR7/8 ligand (R848) in a dose‐dependent manner. Furthermore, when co‐cultured with CD4⁺ T cells, TLR8 ligands inhibited TL1A production, resulting in almost complete inhibition of IFN‐γ production by the CD4⁺ T cells. Furthermore, we demonstrate that IFN‐α is not required for this suppressive effect by TLR8 signaling. Our data demonstrate for the first time a direct interaction between TLR and TL1A signaling pathways. TLR8 activation may be an important, novel pathway for targeted treatment of Th1‐mediated diseases, such as CD.     

Human peripheral blood and bone marrow Epstein–Barr virus‐specific T‐cell repertoire in latent infection reveals distinct memory T‐cell subsets

EBV infection leads to life‐long viral persistence. Although EBV infection can result in chronic disease and malignant transformation, most carriers remain disease‐free as a result of effective control by T cells. EBV‐specific IFN‐γ‐producing T cells could be demonstrated in acute and chronic infection as well as during latency. Recent studies, however, provide evidence that assessing IFN‐γ alone is insufficient to assess the quantity and quality of a T‐cell response. Using overlapping peptide pools of latent EBV nuclear antigen 1 and lytic BZLF‐1 protein and multicolor flow cytometry, we demonstrate that the majority of ex vivo EBV‐reactive T cells in healthy virus carriers are indeed IL‐2‐ and/or TNF‐producing memory cells, the latter being significantly more frequent in BM. After in vitro expansion, a substantial number of EBV‐specific CD4⁺ and CD8⁺ T cells retained a CC‐chemokine receptor 7 (CCR7)‐positive memory phenotype. Based on their cytokine profiles, six different EBV‐specific T‐cell subsets could be distinguished with TNF‐single or TNF/IL‐2‐double producing cells expressing the highest CCR7 levels resembling early‐differentiated memory T cells. Our study delineates the memory T‐cell profile of a protective immune response and provides a basis for analyzing T‐cell responses in EBV‐associated diseases.     

IL‐15 is critical for the maintenance and innate functions of self‐specific CD8+ T cells

IL‐15 is a pleiotropic cytokine involved in host defense as well as autoimmunity. IL‐15‐deficient mice show a decrease of memory phenotype (MP) CD8⁺ T cells, which develop naturally in naïve mice and whose origin is unclear. It has been shown that self‐specific CD8⁺ T cells developed in male H‐Y antigen‐specific TCR transgenic mice share many similarities with naturally occurring MP CD8⁺ T cells in normal mice. In this study, we found that H‐Y antigen‐specific CD8⁺ T cells in male but not female mice decreased when they were crossed with IL‐15‐deficient mice, mainly due to impaired peripheral maintenance. The self‐specific TCR transgenic CD8⁺ T cells developed in IL‐15‐deficient mice showed altered surface phenotypes and reduced effector functions ex vivo. Bystander activation of the self‐specific CD8⁺ T cells was induced in vivo during infection with Listeria monocytogenes, in which proliferation but not IFN‐γ production was IL‐15‐dependent. These results indicated important roles for IL‐15 in the maintenance and functions of self‐specific CD8⁺ T cells, which may be included in the naturally occurring MP CD8⁺ T‐cell population in naïve normal mice and participate in innate host defense responses.     

Direct recognition of LPS by human but not murine CD8+ T cells via TLR4 complex

LPS comprises a major PAMP and is a key target of the immune system during bacterial infection. While LPS can be recognised by innate immune cells via the TLR4 complex, it is unknown whether T lymphocytes, especially CD8⁺ T cells are also capable of doing so. We report here that naïve human CD8⁺ T cells, after activation by TCR stimulation, express surface TLR4 and CD14. These activated CD8⁺ T cells can then secrete high concentrations of IFN‐γ, granzyme and perforin in response to LPS. These effects can be specifically inhibited using siRNA for TLR4. Furthermore, LPS can synergise with IL‐12 to polarise the CD8⁺ T cells into cytotoxic T‐cell 1 (Tc1) that produce IFN‐γ but not IL‐4, with or without TCR activation. Moreover, CD8⁺CD45RO⁺ memory T cells constitutively expressed TLR4 and markedly enhanced IFN‐γ production when stimulated with LPS. In contrast, activated murine CD8⁺ T cells lack TLR4 and CD14 expression and fail to respond to LPS for proliferation and cytokine production. Thus, human but not murine CD8⁺ T cells are able to directly recognise bacterial LPS via LPS receptor complex and TLR4 provides a novel signal for the activation of effector and memory human CD8⁺ T cells.     

IFN‐γ‐STAT1 signal regulates the differentiation of inducible Treg: Potential role for ROS‐mediated apoptosis

Regulatory CD4⁺ T cells are important for the homeostasis of immune cells, and their absence correlates with autoimmune disorders. However, how the immune system regulates Treg homeostasis remains unclear. We found that IFN‐γ‐deficient‐mice had more forkhead box P3 (FOXP3⁺) cells than WT mice in all secondary lymphoid organs except the thymus. However, T‐bet‐ or IL‐4Rα‐deficient mice did not show a similar increase. In vitro differentiation studies showed that conversion of naïve T cells into FOXP3⁺ cells (neo‐generated inducible Treg (iTreg)) by TGF‐β was significantly inhibited by IFN‐γ in a STAT‐1‐dependent manner. Moreover, an in vivo adoptive transfer study showed that inhibition of FOXP3⁺ iTreg generation by IFN‐γ was a T‐cell autocrine effect. This inhibitory effect of IFN‐γ on iTreg generation was significantly abrogated after N‐acetyl‐L ‐cysteine treatment both in vitro and in vivo, indicating that IFN‐γ regulation of iTreg generation is dependent on ROS‐mediated apoptosis. Therefore, our results suggest that autocrine IFN‐γ can negatively regulate the neo‐generation of FOXP3⁺ iTreg through ROS‐mediated apoptosis in the periphery.     

Squalene emulsion potentiates the adjuvant activity of the TLR4 agonist,GLA, via inflammatory caspases,IL‐18, and IFN‐γ

The synthetic TLR4 agonist glucopyranosyl lipid adjuvant (GLA) is a potent Th1‐response‐inducing adjuvant when formulated in a squalene oil‐in‐water emulsion (SE). While the innate signals triggered by TLR4 engagement are well studied, the contribution of SE remains unclear. To better understand the effect of SE on the adjuvant properties of GLA‐SE, we compared the innate and adaptive immune responses elicited by immunization with different formulations: GLA without oil, SE alone or the combination, GLA‐SE, in mice. Within the innate response to adjuvants, only GLA‐SE displayed features of inflammasome activation, evidenced by early IL‐18 secretion and IFN‐γ production in memory CD8⁺ T cells and neutrophils. Such early IFN‐γ production was ablated in caspase‐1/11^?/? mice and in IL‐18R1^?/? mice. Furthermore, caspase‐1/11 and IL‐18 were also required for full Th1 CD4⁺ T‐cell induction via GLA‐SE. Thus, we demonstrate that IL‐18 and caspase‐1/11 are components of the response to immunization with the TLR4 agonist/squalene oil‐in‐water based adjuvant, GLA‐SE, providing implications for other adjuvants that combine oils with TLR agonists.     

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.     

CD161++CD8+ T cells,including the MAIT cell subset,are specifically activated by IL‐12+IL‐18 in a TCR‐independent manner

CD161⁺⁺CD8⁺ T cells represent a novel subset that is dominated in adult peripheral blood by mucosal‐associated invariant T (MAIT) cells, as defined by the expression of a variable‐α chain 7.2 (Vα7.2)‐Jα33 TCR, and IL‐18Rα. Stimulation with IL‐18+IL‐12 is known to induce IFN‐γ by both NK cells and, to a more limited extent, T cells. Here, we show the CD161⁺⁺ CD8⁺ T‐cell population is the primary T‐cell population triggered by this mechanism. Both CD161⁺⁺Vα7.2⁺ and CD161⁺⁺Vα7.2^? T‐cell subsets responded to IL‐12+IL‐18 stimulation, demonstrating this response was not restricted to the MAIT cells, but to the CD161⁺⁺ phenotype. Bacteria and TLR agonists also indirectly triggered IFN‐γ expression via IL‐12 and IL‐18. These data show that CD161⁺⁺ T cells are the predominant T‐cell population that responds directly to IL‐12+IL‐18 stimulation. Furthermore, our findings broaden the potential role of MAIT cells beyond bacterial responsiveness to potentially include viral infections and other inflammatory stimuli.     

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.     

Predominance of heterosubtypic IFN‐γ‐only‐secreting effector memory T cells in pandemic H1N1 naive adults

The 2009/10 pandemic (pH1N1) highlighted the need for vaccines conferring heterosubtypic immunity against antigenically shifted influenza strains. Although cross‐reactive T cells are strong candidates for mediating heterosubtypic immunity, little is known about the population‐level prevalence, frequency, and cytokine‐secretion profile of heterosubtypic T cells to pH1N1. To assess this, pH1N1 sero‐negative adults were recruited. Single‐cell IFN‐γ and IL‐2 cytokine‐secretion profiles to internal proteins of pH1N1 or live virus were enumerated and characterised. Heterosubtypic T cells recognising pH1N1 core proteins were widely prevalent, being detected in 90% (30 of 33) of pH1N1‐naïve individuals. Although the last exposure to influenza was greater than 6 months ago, the frequency and proportion of the IFN‐γ‐only‐secreting T‐cell subset was significantly higher than the IL‐2‐only‐secreting subset. CD8⁺ IFN‐γ‐only‐secreting heterosubtypic T cells were predominantly CCR7^?CD45RA^? effector‐memory phenotype, expressing the tissue‐homing receptor CXCR3 and degranulation marker CD107. Receipt of the 2008–09 influenza vaccine did not alter the frequency of these heterosubtypic T cells, highlighting the inability of current vaccines to maintain this heterosubtypic T‐cell pool. The surprisingly high prevalence of pre‐existing circulating pH1N1‐specific CD8⁺ IFN‐γ‐only‐secreting effector memory T cells with cytotoxic and lung‐homing potential in pH1N1‐seronegative adults may partly explain the low case fatality rate despite high rates of infection of the pandemic in young adults.     

Evidence for eomesodermin‐expressing innate‐like CD8+ KIR/NKG2A+ T cells in human adults and cord blood samples

Polyclonal CD8⁺ T cells, with a marked innate/memory phenotype, high eomesodermin (Eomes) expression, and the capacity to generate IFN‐γ rapidly without prior exposure to antigen, have been described in mice. However, even though a pool of human CD8⁺ T cells expressing killer Ig‐like receptors (KIRs) was recently documented, the existence of a human equivalent of murine innate/memory CD8⁺ T cells remains to be established. Here, we provide evidence for a population of KIR/NKG2A⁺CD8⁺ T cells in healthy human adults sharing the same features, namely increased Eomes expression, prompt IFN‐γ production in response to innate‐like stimulation by IL‐12+IL‐18, and a potent antigen‐independent cytotoxic activity along with a preferential terminally differentiated effector memory phenotype. None of the above functional characteristics applied to the KIR/NKG2A^? fraction of the Eomes⁺CD8⁺ T‐cell population, thereby underlining the ability of KIR/NKG2A to distinguish between “innate/memory‐like” and “conventional/memory” pools of CD8⁺ T cells. Remarkably, KIR/NKG2A⁺Eomes⁺CD8⁺ T cells with innate‐like functions and a memory/terminally differentiated effector memory phenotype were also identified in human cord blood, suggesting that their development did not depend on cognate antigens. Taken together, our results support the conclusion that CD8⁺ T cells co‐expressing Eomes and KIR/NKG2A may represent a new, functionally distinct “innate/memory‐like” subset in humans.     

CCR6 and NK1.1 distinguish between IL‐17A and IFN‐γ‐producing γδ effector T cells

γδ T cells are a potent source of innate IL‐17A and IFN‐γ, and they acquire the capacity to produce these cytokines within the thymus. However, the precise stages and required signals that guide this differentiation are unclear. Here we show that the CD24^low CD44^high effector γδ T cells of the adult thymus are segregated into two lineages by the mutually exclusive expression of CCR6 and NK1.1. Only CCR6⁺ γδ T cells produced IL‐17A, while NK1.1⁺ γδ T cells were efficient producers of IFN‐γ but not of IL‐17A. Their effector phenotype correlated with loss of CCR9 expression, particularly among the NK1.1⁺ γδ T cells. Accordingly, both γδ T‐cell subsets were rare in gut‐associated lymphoid tissues, but abundant in peripheral lymphoid tissues. There, they provided IL‐17A and IFN‐γ in response to TCR‐specific and TCR‐independent stimuli. IL‐12 and IL‐18 induced IFN‐γ and IL‐23 induced IL‐17A production by NK1.1⁺ or CCR6⁺ γδ T cells, respectively. Importantly, we show that CCR6⁺ γδ T cells are more responsive to TCR stimulation than their NK1.1⁺ counterparts. In conclusion, our findings support the hypothesis that CCR6⁺ IL‐17A‐producing γδ T cells derive from less TCR‐dependent selection events than IFN‐γ‐producing NK1.1⁺ γδ T cells.     

Effector T‐cell differentiation during viral and bacterial infections: Role of direct IL‐12 signals for cell fate decision of CD8+ T cells

To study the role of IL‐12 as a third signal for T‐cell activation and differentiation in vivo, direct IL‐12 signaling to CD8⁺ T cells was analyzed in bacterial and viral infections using the P14 T‐cell adoptive transfer model with CD8⁺ T cells that lack the IL‐12 receptor. Results indicate that CD8⁺ T cells deficient in IL‐12 signaling were impaired in clonal expansion after Listeria monocytogenes infection but not after infection with lymphocytic choriomeningitis virus, vaccinia virus or vesicular stomatitis virus. Although limited in clonal expansion after Listeria infection, CD8⁺ T cells deficient in IL‐12 signaling exhibited normal degranulation activity, cytolytic functions, and secretion of IFN‐γ and TNF‐α. However, CD8⁺ T cells lacking IL‐12 signaling failed to up‐regulate KLRG1 and to down‐regulate CD127 in the context of Listeria but not viral infections. Thus, direct IL‐12 signaling to CD8⁺ T cells determines the cell fate decision between short‐lived effector cells and memory precursor effector cells, which is dependent on pathogen‐induced local cytokine milieu.     

Toll‐like receptor 2 agonist Pam3CSK4 enhances the induction of antigen‐specific tolerance via the sublingual route

Background Sublingual immunotherapy (SLIT) has been established in humans as a safe and efficacious treatment for type I respiratory allergies. Objective In this study, we compared three Toll‐like receptor (TLR) 2 ligands (Pam3CSK4, Porphyromonas gingivalis lipopolysaccharide and lipoteichoic acid) as potential adjuvants for sublingual allergy vaccines. Methods These molecules were tested in co‐cultures of adjuvant‐pre‐treated dendritic cells (DCs) with murine naïve CD4⁺ T lymphocytes. Patterns of cytokine production, phenotype, proliferation and gene expression were analysed by ELISA, cytofluorometry and quantitative PCR, respectively. TLR2 ligands were subsequently tested in a model of SLIT in BALB/c mice sensitized with ovalbumin (OVA). Results Among the three TLR2 ligands tested, the synthetic lipopeptide Pam3CSK4 is the most potent inducer of IL‐12p35 and IL‐10 gene expression in murine bone marrow‐derived DCs, as well as in purified oral myeloid DCs. Only Pam3CSK4‐treated DCs induce IFN‐γ and IL‐10 secretion by naïve CD4⁺ T cells. Sublingual administration of Pam3CSK4 together with the antigen in BALB/c mice sensitized to OVA decreases airway hyperresponsiveness as well as OVA‐specific T‐helper type 2 (Th2) responses in cervical lymph nodes dramatically. Conclusion Pam3CSK4 induces Th1/regulatory T cell responses, and as such, is a valid candidate adjuvant for sublingual allergy vaccines.