Monomer hapten and hapten‐specific IgG inhibit mast cell activation evoked by multivalent hapten with different mechanisms

Aggregation of IgE bound to high affinity IgE receptor (FcεRI) by multivalent antigen induces mast cell activation. Reportedly, disaggregation of aggregated FcεRI immediately terminated degranulation, and formation of co‐ligated FcεRI and low affinity IgG receptor FcγRIIB blocked degranulation by inhibitory signal via SH2‐containing inositol 5’‐phosphatase 1 (SHIP1) phosphorylation. However, their molecular mechanisms to inhibit mast cell activation have been unclear in detail. Herein, we found that addition of excess monomeric hapten (TNP‐alanine) to multivalent antigen (TNP‐OVA)‐activated rat basophilic leukemia cells and mouse bone marrow‐derived mast cells induced immediate and transient Syk dephosphorylation, which was previously phosphorylated by TNP‐OVA addition. Syk dephosphorylation correlated to rapidly decreased intracellular Ca²⁺ concentrations ([Ca²⁺]_i), terminated degranulation, and suppressed cytokine production through inhibition of Akt and ERK phosphorylation. Addition of hapten‐specific IgG monoclonal antibody (anti‐TNP IgG1) to activated mast cells induced translocation of SHIP1 to the plasma membrane and its phosphorylation, indicating that co‐ligation of FcεRI and FcγRIIB after FcεRI aggregation can lead to SHIP1 activation. SHIP1 phosphorylation led to gradually decreased [Ca²⁺]_i, weak inhibition of degranulation, and strong inhibition of cytokine production. Our findings clearly show the inhibitory mechanism of cell function in activated mast cells by operating Fc receptor crosslinking.     

The imbalance of Th17/Th1/Tregs in patients with type 2 diabetes: relationship with metabolic factors and complications

Immune disorders are linked to the development of type 2 diabetes (T2D) and its complications. The relationship of CD4⁺CD25^hi T regulatory cells (Treg) and pro-inflammatory Th17 and Th1 subsets in T2D patients with metabolic disorders and complications need to be determined. The ratios of CD4⁺CD25^hi Treg/Th17 cells and CD4⁺CD25^hi Treg/Th1 cells, but not Th17/Th1 cells, were significantly decreased in T2D patients. The thymic output CD4⁺Foxp3⁺Helios⁺ Tregs were normal but peripheral induced CD4⁺Foxp3⁺Helios⁻ Tregs were decreased in T2D patients. The Bcl-2/Bax ratio decreased in CD4⁺CD25^hi Tregs in T2D patients, supporting the increased sensitivity to cell death of these cells in T2D. CD4⁺CD25^hiCD127⁻ Tregs in T2D patients with microvascular complications were significantly less than T2D patients with macrovascular complications. Importantly, CD4⁺CD25^hiCD127⁻ Tregs were positively correlated with plasma IL-6, whereas IL-17⁺CD4⁺cells were negatively related to high-density lipoprotein (HDL). Our data offered evidence for the skewed balance of anti- and pro-inflammatory T cell subsets in T2D patients and identified that HDL closely modulate T cell polarization. These results opened an alternative explanation for the substantial activation of immune cells as well as the development of T2D and complications, which may have significant impacts on the prevention and treatment of T2D patients.     

Basophils are potent antigen‐presenting cells that selectively induce Th2 cells

Basophils and mast cells are important effector cells in helminth‐infected host and IgE‐mediated allergic inflammation. Although they have the same progenitors, basophils and mast cells complete their terminal differentiation in the bone marrow and peripheral tissues, respectively, and only basophils circulate in the blood. Although it is recognized that basophils are important for Th2 responses, and it is also well established that IL‐4 is required for Th2 differentiation from naïve CD4⁺ T cells, the nature of the cells that produce “early” IL‐4, remained elusive until recently. Three groups independently demonstrated that basophils are the predominant APC in inducing Th2 response against helminth parasites and allergens. Basophils express MHC class II and CD80/86, have the potential to take‐up and process protein Ag (particularly Ag–IgE complex) and to present peptide in the context of MHC class II, and to produce IL‐4. These Ag‐pulsed basophils induce the development of Th2 cells both in vitro and in vivo. Thus, basophils contribute to Th2/IgE response by the production of IL‐4 and presentation of MHC class II/peptide complex to naïve CD4⁺ T cells, in contrast to the Th1‐inducing action of DC. In this review, we summarize what is known regarding basophil function in allergy and parasite infection, examine the novel Ag‐presenting function of basophils and discuss potential clinical implications of this finding.     

Mast cells have no impact on cutaneous leishmaniasis severity and related Th2 differentiation in resistant and susceptible mice

The genus leishmania comprises different protozoan parasites which are causative agents of muco‐cutaneous and systemic, potentially lethal diseases. After infection with the species Leishmania major, resistant mice expand Th1 cells which stimulate macrophages for Leishmania destruction. In contrast, susceptible mice generate Th2 cells which deactivate macrophages, leading to systemic spread of the pathogens. Th‐cell differentiation is determined within the first days, and Th2 cell differentiation requires IL‐4, whereby the initial IL‐4 source is often unknown. Mast cells are potential sources of IL‐4, and hence their role in murine leishmaniasis has previously been studied in mast cell‐deficient Kit mutant mice, although these mice display immunological phenotypes beyond mast cell deficiency. We therefore readdressed this question by infecting Kit‐independent mast cell‐deficient mice that are Th1 (C57BL/6 Cpa^Cre) or Th2 (BALB/c Cpa^Cre) prone with L. major. Using different parasite doses and intra‐ or subcutaneous infection routes, the results demonstrate no role of mast cells on lesion size development, parasite load, immune cell phenotypes expanding in draining lymph nodes, and cytokine production during murine cutaneous leishmaniasis. Thus, other cell types such as ILCs or T cells have to be considered as primary source of Th2‐driving IL‐4.     

TLR ligands of ryegrass pollen microbial contaminants enhance Th1 and Th2 responses and decrease induction of Foxp3hi regulatory T cells

Microbial contamination of grass pollens could affect sensitization, subsequent allergic response, and efficacy of allergen‐specific immunotherapy. We investigated whether bacterial immunomodulatory substances can direct PBMC responses of allergic and nonatopic subjects against ryegrass pollen (RGP) toward Th1, Th2, or regulatory T (Treg) cells. Aqueous extracts of RGP with high or low LPS were fractionated into large and small molecular weight (MW) components by diafiltration. CFSE‐labeled PBMCs from allergic and nonatopic subjects were stimulated with RGP extracts (RGPEs) and analyzed for cytokine secretion and T‐cell responses. High LPS RGPE increased IFN‐γ⁺ Th1 and IL‐4⁺ Th2 effector cell induction and consistently decreased CD4⁺Foxp3^hi Treg‐cell induction. IL‐10‐producing T‐cell frequency was unaltered, but IL‐10 secretion was increased by high LPS RGPE. RGPE‐stimulation of TLR‐transfected cell lines revealed that high LPS pollen also contained a TLR2‐ligand, and both batches a TLR9‐ligand. Beta‐1,3‐glucans were detected in large and small MW fractions and were also T‐cell stimulatory. In conclusion, coexposure to allergen and proinflammatory microbial stimuli does not convert an established Th2‐ into a Th1‐response. Instead, proinflammatory responses are exacerbated and Foxp3^hi Treg‐cell induction is decreased. These findings show that adjuvants for specific immunotherapy should enhance Treg cells rather than target immune deviation from Th2 to Th1.     

Altered expression of IL‐18 binding protein and IL‐18 receptor in basophils and mast cells of asthma patients

IL ‐18 is likely to contribute to asthma. However, little is known regarding the role of IL ‐18 binding protein (BP ) and IL ‐18 receptor (R) in asthma. Because the action of IL ‐18 in the body is regulated by IL ‐18BP and mast cells and basophils are key cell types involved in asthma, we investigated the expression of IL ‐18, IL ‐18BP and IL ‐18R in basophils and mast cells using flow cytometry and a mouse asthma model. We found that among basophils, approximately 53% and 51% were IL ‐18⁺, 85% and 81% were IL ‐18BP ⁺ basophils, and 19.8% and 8.6% were IL ‐18R⁺ in healthy control (HC ) and asthmatic blood, respectively. The allergens tested had little effect on the expression of IL ‐18 and related factors. Only 3.5%, 14.3% and 2.4% of dispersed mast cells expressed IL ‐18, IL ‐18BP and IL ‐18R, respectively, in asthmatic sputum. In a mouse asthma model, OVA ‐sensitized mice exhibited decreased IL ‐18BP ⁺ but increased IL ‐18R⁺ basophils in their blood. IL ‐18 increased the number of basophils but eliminated IL ‐18BP ⁺ basophils in mouse blood. IL ‐18 increased the number of mast cells and IL ‐18R⁺ mast cells in the lung as well as increased the mast cell numbers and IL ‐18BP ⁺ mast cells in the bronchoalveolar lavage fluid (BALF ) of OVA ‐sensitized mice. Thus, basophils and mast cells may be involved in asthma pathogenesis via an IL ‐18‐associated mechanism.     

Maturation of mast cell progenitors to mucosal mast cells during allergic pulmonary inflammation in mice

In contrast to resident constitutive mast cells (CMCs), mucosal MCs (MMCs) appear in the lung and trachea of sensitized mice only following inhalation challenge. We monitored the influx and maturation of MCs by their expression of Kit, FcɛRI, β7-integrin and side scatter (SSC) by flow cytometry. Influx of MC progenitors (MCps) (FcɛRI^lo, Kit^int, β7^hi, and SSC^lo) peaks 1 day after challenges and subsides to baseline by day 7 after challenge. The mature MMCs appear as a distinct population on day 7 and peak at day 14 with higher SSC and FcɛRI expression, but lower β7 and Kit expression. A distinct transitional population is present between 1 and 7 days after challenge. Maturation occurs more rapidly in the trachea. The resident tracheal CMCs had higher SSC, FcɛRI, and Kit and lower β7-integrin expression than the MMCs. By histology, the MMCs follow similar kinetics to the flow cytometry-identified mature MMCs and are notably persistent for >42 days. Steroid treatment reduced inflammation and MCp influx but had no effect on established MMCs. Thus, changes in SSC, FcɛRI, and Kit together with the expression of αE/α4:β7-integrins characterizes the development of induced MMCs from MCps and distinguishes them from resident CMCs in the trachea and large airways.     

IL-13-producing Th1 and Th17 cells characterize adaptive responses to both self and foreign antigens

In helper T cells, IL‐13 is traditionally considered a Th2‐type cytokine that is coexpressed with IL‐4. Using mouse models of immunization and autoimmunity, we demonstrate that IL‐13 is frequently uncoupled from IL‐4, and that it can be produced by both IFN‐γ⁺ Th1 cells and IL‐17⁺ Th17 cells. We report that these IL‐13‐producing Th1 and Th17 cells are distinct from classical IL‐4⁺ Th2 cells and that they are relatively common, appearing in the context of both protective and pathogenic T‐cell responses. We also demonstrate that IL‐13 and Th2‐type cytokines can have important consequences in Th1‐ and Th17‐dominated settings, such as lymphopenia‐induced autoimmune disease, where they can be either pro‐ or anti‐inflammatory, depending on whether they act on innate or adaptive immune cells. Taken together, our studies indicate that IL‐13 production is more widespread than previously appreciated and that blocking this cytokine may have therapeutic benefits even in settings where traditional IL‐4‐driven Th2‐type responses are not evident.     

Resolving Salmonella infection reveals dynamic and persisting changes in murine bone marrow progenitor cell phenotype and function

The generation of immune cells from BM precursors is a carefully regulated process. This is essential to limit the potential for oncogenesis and autoimmunity yet protect against infection. How infection modulates this is unclear. Salmonella can colonize systemic sites including the BM and spleen. This resolving infection has multiple IFN‐γ‐mediated acute and chronic effects on BM progenitors, and during the first week of infection IFN‐γ is produced by myeloid, NK, NKT, CD4⁺ T cells, and some lineage‐negative cells. After infection, the phenotype of BM progenitors rapidly but reversibly alters, with a peak ～30‐fold increase in Sca‐1^hi progenitors and a corresponding loss of Sca‐1^lo/int subsets. Most strikingly, the capacity of donor Sca‐1^hi cells to reconstitute an irradiated host is reduced; the longer donor mice are exposed to infection, and Sca‐1^hic‐kit^int cells have an increased potential to generate B1a‐like cells. Thus, Salmonella can have a prolonged influence on BM progenitor functionality not directly related to bacterial persistence. These results reflect changes observed in leucopoiesis during aging and suggest that BM functionality can be modulated by life‐long, periodic exposure to infection. Better understanding of this process could offer novel therapeutic opportunities to modulate BM functionality and promote healthy aging.     

Interaction between prostaglandin D2 and chemoattractant receptor‐homologous molecule expressed on Th2 cells mediates cytokine production by Th2 lymphocytes in response to activated mast cells

The mechanisms by which immunologically activated mast cells stimulate the production of proinflammatory cytokines by T helper type 2 (Th2) lymphocytes were investigated in a human cell culture system. Supernatants collected from cord blood‐derived mast cells after treatment with immunoglobulin E (IgE)/anti‐IgE contained an activity that stimulated the production of interleukin (IL)‐4, IL‐5 and IL‐13 (both mRNA and protein) by Th2 lymphocytes. This activity was not detected in supernatants from unactivated mast cells and its production was inhibited by treatment of activated mast cells with the cyclo‐oxygenase inhibitor diclofenac. The concentration of diclofenac used inhibited completely the production of prostaglandin D₂ (PGD₂) but did not inhibit the release of histamine or leukotriene C₄. The effect of supernatants from activated mast cells was mimicked by exogenous PGD₂ at concentrations similar to those detected in the cultures of activated mast cells, and addition of exogenous PGD₂ to supernatants from diclofenac‐treated mast cells restored their ability to stimulate Th2 cytokine production. The ability of the mast cell supernatants to stimulate production of Th2 cytokines was not affected by addition of diclofenac to the Th2 cells directly, indicating that the production, but not the action, of the factor was sensitive to diclofenac treatment. Inhibition of chemoattractant receptor‐homologous molecule expressed on Th2 cells (CRTH2) abolished the effect of the mast cell supernatants on Th2 cytokine production. These data indicate that mast cells have the ability to stimulate Th2 cells to elaborate cytokines independently of T cell receptor activation or co‐stimulation and this response is mediated by PGD₂ acting upon CRTH2 expressed by Th2 cells.     

The immunobiology of Th1 polarization in high-pathology schistosomiasis

Summary: Schistosomiasis is a serious global helminthic disease, in which the main immunopathology consists of a granulomatous and fibrosing reaction against tissue‐trapped parasite eggs. The severity of this inflammatory process, the product of a CD4⁺ T‐cell‐mediated immune response against parasite egg antigens, is, however, markedly uneven, both in human patients and among mouse strains in an experimental model. Severe schistosomiasis is associated with persistently elevated pro‐inflammatory T‐helper‐1 (Th1)‐type cytokines, whereas milder pathology is present when Th2 cytokines dominate. This scenario is supported by the pronounced pathology resulting from the obliteration of pathways that facilitate Th2 differentiation and by the development of more intense lesions in mouse strains that fail to downregulate the Th1 response. Genetically prone high‐pathology mice have a higher proportion of CD4⁺ T cells in lymph nodes and granulomas, in which the Th1 phenotype is driven by interleukin‐12; they also develop a dominant repertoire against peptide 234–246 of the major Sm‐p40 egg antigen, utilizing a strikingly restricted T‐cell receptor structure that involves Vα11.3β8. In turn, low‐pathology mice exhibit enhanced CD4⁺ T‐cell apoptosis, which contributes to limit pathology. The definition of distinctive immune profiles associated with polar forms of schistosomiasis opens opportunities for targeted immuno‐intervention in individuals suffering from or at risk of severe disease.     

Dual effects of the alloresponse by Th1 and Th2 cells on acute and chronic rejection of allotransplants

The contribution of direct and indirect alloresponses by CD4⁺ Th1 and Th2 cells in acute and chronic rejection of allogeneic transplants remains unclear. In the present study, we addressed this question using a transplant model in a single MHC class I‐disparate donor–recipient mouse combination. BALB/c‐dm2 (dm2) mutant mice do not express MHC class I L^d molecules and reject acutely L^d+ skin grafts from BALB/c mice. In contrast, BALB/c hearts placed in dm2 mice are permanently accepted in the absence of chronic allograft vasculopathy. In this model, CD4⁺ T cells are activated following recognition of a donor MHC class I determinant, L^d 61–80, presented by MHC Class II A^d molecules on donor and recipient APC. Pre‐transplantation of recipients with L^d 61–80 peptide emulsified in complete Freund's adjuvant induced a Th1 response, which accelerated the rejection of skin allografts, but it had no effect on cardiac transplants. In contrast, induction of a Th2 response to the same peptide abrogated the CD8⁺ cytotoxic T cells response and markedly delayed the rejection of skin allografts while it induced de novo chronic rejection of heart transplants. This shows that Th2 cells activated via indirect allorecognition can exert dual effects on acute and chronic rejection of allogeneic transplants.     

Effect of CD40/CD40L signaling on IL-10-producing regulatory B cells in Chinese children with Henoch-Schönlein purpura nephritis

The aim of the present study was to examine the role and mechanism of interleukin-10 (IL-10)-producing regulatory B cells (B10 cells) in the pathogenesis of Henoch-Schönlein purpura nephritis (HSPN). We examined the percentage of B10 cells, CD19⁺CD24^hiCD38^hi B cells, CD19⁺CD24^hiCD27⁺ B cells, Th17 cells, and T regulatory (Treg) cells within the peripheral blood mononuclear cell (PBMC) population in healthy subjects and HSP/HSPN patients. The percentage of B10 cells and CD19⁺CD24^hiCD38^hi B cells was reduced in HSPN patients and that of CD19⁺CD24^hiCD27⁺ B cells was decreased only in HSPN patients with hematuria and proteinuria or massive proteinuria. The expression of IL-10 by B10 cells and their subsets was decreased in HSPN patients and returned to normal levels in HSP/HSPN patients in remission. B10 cells and their subsets negatively correlated with the Th17/Treg ratio. There was no difference in B10pro + B10 cells, Th17 cells, Treg cells, and the Th17/Treg ratio between children with HSP/HSPN and healthy controls after CD40L stimulation. On the other hand, the level of IL-10 expressed by CD19⁺CD40⁺ B cells was decreased in HSPN, and the percentage of B10pro + B10 cells and Treg cells was reduced and that of Th17 cell was increased in the presence of anti-CD40L monoclonal antibody (mAb). Thus, decreased B10 cells and CD19⁺CD24^hiCD38^hi B cells may function as an early marker of renal impairment in HSPN. The dysfunction of B10 cells may play a role in the pathogenesis of HSPN by regulating the Th17/Treg balance. Moreover, the CD40/CD40L signaling pathway may play a role in B10 cell differentiation and functional maturation.     

Mast cell infiltrates in vulvodynia represent secondary and idiopathic mast cell hyperplasias

Mast cell infiltrates in tissues of vulvodynia are common, but they have not been characterized for criteria of neoplastic mast cell disease or correlated with patient's concomitant diseases associated with increased mast cells. Formalin‐fixed specimens of 35 patients with vulvodynia were evaluated immunohistochemically with antibodies to CD 3,4,8,20,117c and human mast cell tryptase, and for WHO‐criteria of neoplastic mastocytosis (>25% spindled mast cell, CD25 expression, point mutations of the c‐kit gene (D816V), and chronically elevated serum tryptase levels). Only 20/35 specimens showed a T‐lymphocyte dominant inflammatory infiltrate on HE‐stained sections, but all showed mast cells. 4/35 biopsies showed <10 mast cells/mm², 15/35 specimens 40–60 mast cells/mm² and 16/35 specimens >60 mast cells/mm² (average 80/mm²). Control tissue contained typically <10 mast cells/mm². Spindling, CD25‐expression, c‐kit gene mutations, or increased serum tryptase levels were not detected. 26/35 (74%) patients had concomitant autoimmune diseases, psoriasis, atopy, various allergies, preceding infections. Independent of the subtype of vulvodynia, the majority of mast cell rich biopsies with >40 mast cells/mm² were classified as a secondary mast cell disorder reflecting an activated immune system in 75% of vulvodynia patients. Patients with increased mast cells may benefit from medical therapy targeting mast cells.     

C5a receptor signalling in dendritic cells controls the development of maladaptive Th2 and Th17 immunity in experimental allergic asthma

The pathways underlying dendritic cell (DC) activation in allergic asthma are incompletely understood. Here we demonstrate that adoptive transfer of ovalbumin-pulsed wild-type (wt) but not of C5a receptor-deficient (C5aR^−/−) bone marrow (BM)-derived DCs (BMDCs) induced mixed T helper type 2 (Th2)/Th17 maladaptive immunity, associated with severe airway hyperresponsiveness, mucus production, and mixed eosinophilic/neutrophilic inflammation. Mechanistically, antigen uptake, processing, and CD11b expression were reduced in C5aR^−/− BMDCs. Further, interleukin (IL)-1β, -6, and -23 production were impaired resulting in reduced Th17 cell differentiation, associated with accelerated activated T-cell death in vitro and in vivo. Surprisingly, we found an increased frequency of CD11b^hiCD11c^intGr1⁺F4/80⁺ cells, expressing arginase and nitric oxide synthase in C5aR^−/− BM preparations. Intratracheal administration of ovalbumin-pulsed wt DCs and sorted CD11b^hiCD11c^intGr1⁺F4/80⁺ C5aR^−/− cells reduced Th2 immune responses in vivo. Together, we uncover novel roles for C5aR in Th17 differentiation, T-cell survival, and differentiation of a DC-suppressor population controlling Th2 immunity in experimental allergic asthma.     

IgE receptors on human lymphocytes III. Expression of IgE receptors on mitogen-stimulated human mononuclear cells

Human peripheral blood mononuclear cells (PBMC) were tested for the expression of Fee-receptor (FcεR) after stimulation with various mitogens in the absence of IgE. FcεR were found on virtually all the cells from 19 Epstein-Barr virus-transformed B cell lines including those derived from cord blood, from one agamma-globulinemic patient and VDS-0 pre-B cells. Hence, the data clearly indicate that FcεR may be expressed on very immature B cells. PBMC cultures stimulated with either pokeweed mitogen (PWM), phytohemagglutinin (PHA) or concanavalin A displayed an early increase of their content in FcεR-bearing cells followed by a decrease to levels below those of the control cultures. After fractionation of the PWM-stimulated cultures into T and B cell-enriched preparations, most of the FcεR⁺ cells were in the B cell fractions and the same low levels of FceR⁺ cells were found in the T cell fractions isolated from the PWM-stimulated and from the control cultures. Double-labeling experiments, employing biotinylated F(ab')₂ monoclonal antibody to FcR and either fluorescein isothiocyanate-conjugated B1 or Mo2 monoclonal antibodies, indicated that PWM mainly exerted its effect on B cells and on monocytes. This effect was T cell dependent and it was mediated by soluble factors of T cell origin. At the peak of the PHA or concanavalin A response, most of the FceR-bearing cells were found in the B cell fraction but the T cells isolated from mitogen-stimulated cultures contained significantly more FcεR⁺ cells than those from the control cultures, suggesting that T cell mitogens had increased the expression of FcεR on some T cells. This view was supported by the finding of a higher proportion of FceR⁺ cells in PHA-stimulated than in control cultures of highly purified T cells with a maximum response at the end of the culture period. Double-labeling experiments at the peak (day 2) of the peripheral blood mononuclear cell response indicated that the expression of FcεR was increased on B cells (Bl⁺) and on monocytes (Mo2⁺). By using the same approach at the peak of the T cell response (day 7), it was found that T cells isolated from PHA-stimulated cultures expressed more FcεR than those isolated from control cultures. Moreover, in unstimulated cultures, FcεR was mainly expressed on T helper cells (Leu 3⁺) whereas in PHA-stimulated cultures FcεR was expressed on both T helper and T suppressor/cytotoxic cells (Leu 2⁺).     

T-zone localized monocyte-derived dendritic cells promote Th1 priming to Salmonella

Control of intracellular Salmonella infection requires Th1 priming and IFN‐γ production. Here, we show that efficient Th1 priming after Salmonella infection requires CD11c⁺CD11b^hiF4/80⁺ monocyte‐derived dendritic cells (moDCs). In non‐infected spleens, moDCs are absent from T‐cell zones (T zones) of secondary lymphoid tissues, but by 24 h post‐infection moDCs are readily discernible in these sites. The accumulation of moDCs is more dependent upon bacterial viability than bacterial virulence. Kinetic studies showed that moDCs were necessary to prime but not sustain Th1 responses, while ex vivo studies showed that antigen‐experienced moDCs were sufficient to induce T‐cell proliferation and IFN‐γ production via a TNF‐α‐dependent mechanism. Importantly, moDCs and cDCs when co‐cultured induced superior Th1 differentiation than either subset alone, and this activity was independent of TNF‐α. Thus, optimal Th1 development to Salmonella requires the rapid accumulation of moDCs within T zones and their collaboration with cDCs.