Oligosymptomatic long-term carriers of SARS-CoV-2 display impaired innate resistance but increased high-affinity anti-spike antibodies.

The vast spectrum of clinical features of COVID-19 keeps challenging scientists and clinicians. Low resistance to infection might result in long-term viral persistence, but the underlying mechanisms remain unclear. Here, we studied the immune response of immunocompetent COVID-19 patients with prolonged SARS-CoV-2 infection by immunophenotyping, cytokine and serological analysis. Despite viral loads and symptoms comparable to regular mildly symptomatic patients, long-term carriers displayed weaker systemic IFN-I responses and fewer circulating pDCs and NK cells at disease onset. Type 1 cytokines remained low, while type-3 cytokines were in turn enhanced. Of interest, we observed no defects in antigen-specific cytotoxic T cell responses, and circulating antibodies displayed higher affinity against different variants of SARS-CoV-2 Spike protein in these patients. The identification of distinct immune responses in long-term carriers adds up to our understanding of essential host protective mechanisms to ensure tissue damage control despite prolonged viral infection.

Relationships of circulating CD4+ T cell subsets and cytokines with the risk of relapse in patients with Crohn's disease.

Background and aims: We aimed to analyze circulating CD4+ T cell subsets and cytokines during the course of Crohn's disease (CD). Methods and results: CD4+ T cell subsets, ultrasensitive C-reactive protein (usCRP), and various serum cytokines (IL-6, IL-8, IL-10, IL-13, IL-17A, IL-23, TNFα, IFNγ, and TGFß) were prospectively monitored every 3 months for 1 year, using multicolor flow cytometry and an ultrasensitive Erenna method in CD patients in remission at inclusion. Relapse occurred in 35 out of the 113 consecutive patients (31%). For patients in remission within 4 months prior to relapse and at the time of relapse, there was no significant difference in Th1, Th17, Treg, and double-positive CD4+ T cell subsets co-expressing either IFNγ and FOXP3, IL-17A and FOXP3, or IFNγ and IL-17A. On the contrary, in patients who remained in remission, the mean frequency and number of double-positive IL-17A+FOXP3+ CD4+ T cells and the level of usCRP were significantly higher (p ≤ 0.01) 1 to 4 months prior to relapse. At the time of relapse, only the IL-6 and usCRP levels were significantly higher (p ≤ 0.001) compared with those patients in remission. On multivariate analysis, a high number of double-positive IL-17A+FOXP3+ CD4+ T cells (≥1.4 cells/mm3) and elevated serum usCRP (≥3.44 mg/L) were two independent factors associated with risk of relapse. Conclusions: Detection of circulating double-positive FOXP3+IL-17A+ CD4+ T cell subsets supports that T cell plasticity may reflect the inflammatory context of Crohn's disease. Whether this subset contributes to the pathogenesis of CD relapse needs further studies.

Intestinal dendritic cell licensing through Toll-like receptor 4 is required for oral tolerance in allergic contact dermatitis.

BACKGROUND: Induction of oral tolerance to haptens is an efficient way to prevent allergic contact dermatitis (ACD) in mice. Toll-like receptor (TLR)-mediated sensing of the microbiota contributes to gut homeostasis, yet whether it contributes to induction of oral tolerance has not been documented. OBJECTIVE: We examined whether oral tolerance to the contact sensitizer 2,4-dinitro-fluorobenzene (DNFB) depends on microbiota/TLRs and evaluated the role of TLR4 on the tolerogenic function of intestinal dendritic cells (DCs). METHODS: Oral tolerance was induced by DNFB gavage in germ-free and mice deficient in several TLRs. Tolerance was assessed by means of suppression of contact hypersensitivity and hapten-specific IFN-γ-producing effector T cells. The tolerogenic function of intestinal DCs was tested by adoptive transfer experiments, ex vivo hapten presentation, and forkhead box p3 regulatory T-cell conversion. RESULTS: Oral tolerance induced by DNFB gavage was impaired in germ-free mice and TLR4-deficient mice. Bone marrow chimeras revealed that TLR4 expression on hematopoietic cells was necessary for oral tolerance induction. TLR4 appeared to be essential for the ability of intestinal dendritic cells from DNFB-fed mice to inhibit ACD on adoptive transfer. Indeed, TLR4 conditioned the in vivo mobilization to mesenteric lymph nodes of intestinal migratory CD103+ DCs carrying oral DNFB, especially the CD103+CD11b+ DC subset expressing the vitamin A-converting enzyme retinaldehyde dehydrogenase and specialized in forkhead box p3-positive regulatory T-cell conversion. CONCLUSIONS: Our data demonstrate that TLR4 conditions induction of oral tolerance to DNFB through licensing tolerogenic gut DCs. Oral biotherapy with TLR4 ligands might be useful to potentiate oral tolerance to haptens and alleviate ACD in human subjects.

Gut Inflammation in Mice Triggers Proliferation and Function of Mucosal Foxp3+ Regulatory T Cells but Impairs Their Conversion from CD4+ T Cells.

BACKGROUND AND AIMS: Regulatory Foxp3+CD4+ T cells [Tregs] have been implicated in the control of colitis in T-cell transfer models, yet their ability to regulate colitis induced by innate immunity and the impact of gut inflammation on their fate and function have been poorly documented. METHODS: Colitis was induced by dextran sodium sulphate in DEREG transgenic mice. Tregs ablation and transfer experiments showd that Tregs could limit the severity of colitis in B6 mice. RESULTS: Gut inflammation resulted in increased number of Tregs in mesenteric lymph nodes [MLN] and colon lamina propria [LP], although their frequency decreased due to massive concomitant leukocyte infiltration. This coincided at both sites with a dramatic increase in Ki67+ Tregs which retained proliferative capacity. Gut inflammation resulted in enhanced suppressive function of Tregs in colon lamina propria and neuropillin-1- [NRP1-] Treg in MLN. Real-time polymerase chain reaction analysis and flow cytometry [using IL10-egfp-reporter mice] showed that compared with NRP1+ Treg, NRP1- Treg express higher levels of IL-10 transcripts and were enriched in IL10-expressing cells both in the steady state and during colitis. Moreover, Treg conversion in vivo from from naïve CD4+ T cells or Treg precursors was impaired in colitic mice. Finally, gut inflammation caused a decrease in intestinal dendritic cells, affecting both CD103+CD11b+ and CD103+CD11b- subsets and affected their Treg conversion capacity. CONCLUSIONS: Together, our data indicate that non-specific colon inflammation triggers proliferation and suppressive function of Tregs in the lamina propria and MLN, but impairs their de novo conversion from CD4+ T cells by intestinal dendritic cells.

Mouse and Human Liver Contain Immunoglobulin A-Secreting Cells Originating From Peyer's Patches and Directed Against Intestinal Antigens.

BACKGROUND & AIMS: The liver receives blood from the gastrointestinal tract through the portal vein, and thereby is exposed continuously to dietary antigens and commensal bacteria. Alcoholic liver disease (ALD) is associated with intestinal dysbiosis, increased intestinal permeability, release of microbes into the portal circulation, and increased serum levels and liver deposits of IgA. We characterized B-cell production of IgA in livers of mice at homeostasis, after oral immunization, in a mouse model of ALD and in human liver samples. METHODS: We performed studies with Balb/c and C57BL/6-Ly5.1 mice, as well as transgenic mice (quasimonoclonal, activation-induced [cytidine] deaminase-Cre-tamoxifen-dependent estrogen receptor 2 [ERT2], Blimp-1-green fluorescent protein [GFP]). C57BL/6-Ly5.1 mice were fed chronic plus binge ethanol to create a model of ALD. Some mice also were given repeated injections of FTY720, which prevents egress of IgA-secreting cells from Peyer's patches. We obtained nontumor liver tissues from patients with colorectal carcinoma undergoing surgery for liver metastases or hepatocellular carcinoma. B cells were isolated from mouse and human liver tissues and analyzed by flow cytometry and enzyme-linked ImmunoSpot (ELISpot). In wild-type and transgenic mice, we traced newly generated IgA-secreting cells at steady state and after oral immunization with 4-hydroxy-3-nitrophenylacetyl (NP)-Ficoll or cholera toxin. IgA responses were also evaluated in our model of ALD. RESULTS: Livers of control mice contained proliferative plasmablasts that originated from Peyer's patches and produced IgAs reactive to commensal bacteria. After oral immunization with cholera toxin or a thymus-independent antigen, a substantial number of antigen-specific IgA-secreting cells was found in the liver. Mice fed ethanol had features of hepatitis and increased numbers of IgA-secreting cells in liver, compared with mice given control diets, as well as higher levels of serum IgA and IgA deposits in liver sinusoids. Injection of FTY720 during ethanol feeding reduced liver and serum levels of IgA and IgA deposits in liver and prevented liver injury. Human liver tissues contained a significant proportion of IgA-producing plasma cells that shared phenotypic and functional attributes with those from mouse liver, including reactivity to commensal bacteria. CONCLUSIONS: Based on studies of mice and human liver tissues, we found the liver to be a site of IgA production by B cells, derived from gut-associated lymphoid tissues. These IgAs react with commensal bacteria and oral antigens. Livers from mice with ethanol-induced injury contain increased numbers of IgA-secreting cells and have IgA deposits in sinusoids. IgAs in the liver could mediate clearance of gut-derived antigens that arrive through portal circulation at homeostasis and protect these organs from pathogens.

Intradermal vaccination with un-adjuvanted sub-unit vaccines triggers skin innate immunity and confers protective respiratory immunity in domestic swine.

Intradermal (ID) vaccination constitutes a promising approach to induce anti-infectious immunity. This route of immunization has mostly been studied with influenza split-virion vaccines. However, the efficacy of ID vaccination for sub-unit vaccines in relation to underlying skin innate immunity remains to be explored for wider application in humans. Relevant animal models that more closely mimic human skin immunity than the widely used mouse models are therefore necessary. Here, we show in domestic swine, which shares striking anatomic and functional properties with human skin, that a single ID delivery of pseudorabies virus (PRV) glycoproteins without added adjuvant is sufficient to trigger adaptive cellular and humoral immune responses, and to confer protection from a lethal respiratory infection with PRV. Analysis of early events at the skin injection site revealed up-regulation of pro-inflammatory cytokine and chemokine genes, recruitment of neutrophils and monocytes and accumulation of inflammatory DC. We further show that the sustained induction of pro-inflammatory cytokine genes results from the combined effects of skin puncture, liquid injection in the dermis and viral antigens. These data highlight that immune protection against respiratory infection can be induced by ID vaccination with a subunit vaccine and reveal that adjuvant requirements are circumvented by the mechanical and antigenic stress caused by ID injection, which triggers innate immunity and mobilization of inflammatory DC at the immunization site. ID vaccination with sub-unit vaccines may thus represent a safe and efficient solution for protection against respiratory infections in swine and possibly also in humans, given the similarity of skin structure and function in both species.

Enrichment of Circulating and Mucosal Cytotoxic CD8+ T Cells Is Associated with Postoperative Endoscopic Recurrence in Patients with Crohn's Disease.

BACKGROUND AND AIMS: Evidence from mouse colitis models indicates that cytotoxic CD8+ T cells [CTL] play a key role in the initiation of gut lesions. We investigated whether changes in CD8+ CTL in blood or lamina propria [LP] of the neoterminal ileum were associated with postoperative endoscopic recurrence of Crohn's disease [CD]. METHODS: A total of 37 CD patients with ileocolonic resection were endoscopically followed up at 6 and 12 months post-surgery. CD8+ T cells were analysed by flow cytometry in blood and ileal LP. RESULTS: Granzyme B- and perforin-producing CD8+ T cells were significantly increased at 6 months in blood and in ileum LP in patients with endoscopic recurrence, as compared with those in remission. At a cutoff point of 45% of CD8+ CTL, the overall accuracies of the frequency of blood granzyme B+ or perforin+ CD8+ T cells to identify patients with postoperative endoscopic recurrence were 77% and 83%, respectively. Interestingly, patients with endoscopic recurrence at 12 months were those showing the highest mucosal CD8+ CTL frequency at 6 months, while still in remission. CONCLUSIONS: Enrichment of cytotoxic CD8+ T cells in blood and ileal mucosa coincides with CD postoperative endoscopic recurrence. This underscores that CD8 CTL may play a pathophysiological role in the initiation of gut lesions during CD.

Plasmacytoid dendritic cells are dispensable for noninfectious intestinal IgA responses in vivo.

Intestinal DCs orchestrate gut immune homeostasis by dampening proinflammatory T-cell responses and inducing anti-inflammatory IgA responses. Although no specific DC subset has been strictly assigned so far to govern IgA response, some candidate subsets emerge. In particular, plasmacytoid DCs (pDCs), which notoriously promote anti-viral immunity and T-cell tolerance to innocuous antigens (Ags), contribute to IgA induction in response to intestinal viral infection and promote T-cell-independent IgA responses in vitro. Here, using two transgenic mouse models, we show that neither short-term nor long-term pDC depletion alters IgA class switch recombination in Peyer's patches and frequency of IgA plasma cells in intestinal mucosa at steady state, even in the absence of T-cell help. In addition, pDCs are dispensable for induction of intestinal IgA plasma cells in response to oral immunization with T-cell-dependent or T-cell-independent Ags, and are not required for proliferation and IgA switch of Ag-specific B cells in GALT. These results show that pDCs are dispensable for noninfectious IgA responses, and suggest that various DC subsets may play redundant roles in the control of intestinal IgA responses.

Intradermal immunisation using the TLR3-ligand Poly (I:C) as adjuvant induces mucosal antibody responses and protects against genital HSV-2 infection.

Development of vaccines able to induce mucosal immunity in the genital and gastrointestinal tracts is a major challenge to counter sexually transmitted pathogens such as HIV-1 and HSV-2. Herein, we showed that intradermal (ID) immunisation with sub-unit vaccine antigens (i.e., HIV-1 gp140 and HSV-2 gD) delivered with Poly(I:C) or CpG1668 as adjuvant induces long-lasting virus-specific immunoglobulin (Ig)-G and IgA antibodies in the vagina and feces. Poly(I:C)-supplemented sub-unit viral vaccines caused minimal skin reactogenicity at variance to those containing CpG1668, promoted a delayed-type hypersensitivity (DTH) to the vaccine and protected mice from genital and neurological symptoms after a lethal vaginal HSV-2 challenge. Interestingly, Poly(I:C12U) (Ampligen), a Poly(I:C) structural analogue that binds to TLR3 but not MDA-5, promoted robust mucosal and systemic IgG antibodies, a weak skin DTH to the vaccine but not IgA responses and failed to confer protection against HSV-2 infection. Moreover, Poly(I:C) was far superior to Poly(I:C12U) at inducing prompt and robust upregulation of IFNß transcripts in lymph nodes draining the injection site. These data illustrate that ID vaccination with glycoproteins and Poly(I:C) as adjuvant promotes long-lasting mucosal immunity and protection from genital HSV-2 infection, with an acceptable skin reactogenicity profile. The ID route thus appears to be an unexpected inductive site for mucosal immunity and anti-viral protection suitable for sub-unit vaccines. This works further highlights that TLR3/MDA5 agonists such as Poly(I:C) may be valuable adjuvants for ID vaccination against sexually transmitted diseases.

Long-term disease course in a patient with severe neonatal IPEX syndrome.

We report here on the clinical, histological and immunological findings regarding a patient with immunodysregulation polyendocrinopathy enteropathy X-linked syndrome who was treated for the first 21 years with a combination of immunosuppressant agents (IS). The potential modalities of care and treatment options in this rare and severe immune-mediated disorder are discussed. So, long-term outcome for IPEX patients can be obtained with immunosuppressive treatment, which is important since the outcome of haematopoietic stem cell transplantation for this population is variable.

Comparative histology and immunohistochemistry of porcine versus human skin.

BACKGROUND: Porcine skin is increasingly being employed as a model of human skin in various research fields, including pharmacology, toxicology and immunology, with particular interest in percutaneous permeation and organ transplantation. Porcine skin shows several anatomical and physiological similarities, but also some differences, with human skin, but few in depth comparative studies are so far available. OBJECTIVES: To study the immunohistochemical properties of normal porcine skin in comparison with human skin. MATERIALS AND METHODS: We performed a histological and immunohistochemical study on frozen and formalin-fixed, paraffin-embedded skin biopsies from domestic swine and normal human skin, using a panel of 93 monoclonal or polyclonal antibodies recognizing various human and porcine skin cell types or structures. RESULTS: We found that several antibodies used to detect normal human skin cells showed equivalent immunoreactivity on normal porcine skin. However, some antibodies commonly used to detect human skin antigens remained unreactive on porcine skin. CONCLUSIONS: Our findings highlight the main immunohistochemical properties of porcine skin in comparison with those of human skin and provide a morphological and immunohistochemical basis useful to researchers using porcine skin.

Regulatory CD4+Foxp3+ T cells control the severity of anaphylaxis.

OBJECTIVE: Anaphylaxis is a life-threatening outcome of immediate-type hypersensitivity to allergen, consecutive to mast cell degranulation by allergen-specific IgE. Regulatory T cells (Treg) can control allergic sensitization and mast cell degranulation, yet their clinical benefit on anaphylactic symptoms is poorly documented. Here we investigated whether Treg action during the effector arm of the allergic response alleviates anaphylaxis. METHODS: We used a validated model of IgE-mediated passive systemic anaphylaxis, induced by intravenous challenge with DNP-HSA in mice passively sensitized with DNP-specific IgE. Anaphylaxis was monitored by the drop in body temperature as well as plasma histamine and serum mMCP1 levels. The role of Treg was analyzed using MHC class II-deficient (Aß(°/°)) mice, treatment with anti-CD25 or anti-CD4 mAbs and conditional ablation of Foxp3(+) Treg in DEREG mice. Therapeutic efficacy of Treg was also evaluated by transfer experiments using FoxP3-eGFP knock-in mice. RESULTS: Anaphylaxis did not occur in mast cell-deficient W/W(v) mutant mice and was only moderate and transient in mice deficient for histamine receptor-1. Defects in constitutive Treg, either genetic or induced by antibody or toxin treatment resulted in a more severe and/or sustained hypothermia, associated with a rise in serum mMCP1, but not histamine. Adoptive transfer of Foxp3(+) Treg from either naïve or DNP-sensitized donors similarly alleviated body temperature loss in Treg-deficient DEREG mice. CONCLUSION: Constitutive Foxp3(+) Treg can control the symptomatic phase of mast cell and IgE-dependent anaphylaxis in mice. This might open up new therapeutic avenues using constitutive rather than Ag-specific Treg for inducing tolerance in allergic patients.

Neopterin is a novel reliable fecal marker as accurate as calprotectin for predicting endoscopic disease activity in patients with inflammatory bowel diseases.

BACKGROUND: Fecal biomarkers have emerged as an important tool for assessing and monitoring disease activity in patients with inflammatory bowel diseases (IBDs). We performed a prospective head-to-head comparison of the diagnostic accuracy of both fecal calprotectin (fCal) and neopterin (fNeo), and serum C-reactive protein in predicting endoscopic disease severity in patients with IBD. METHODS: A total of 133 consecutive patients with IBD (78 Crohn's disease [CD] and 55 ulcerative colitis [UC]) undergoing a colonoscopy provided fecal samples for the measurement of fCal and fNeo concentrations and a blood sample for the serum C-reactive protein measurement. Endoscopic disease activities were scored independently according to the Simple Endoscopic Score for CD in patients with CD and to the Rachmilewitz Index in patients with UC. The respective performances of the fecal markers with respect to endoscopic disease severity were assessed by computing correlations, sensitivities, specificities, and overall accuracies at adjusted cutoffs and also test operating characteristics. RESULTS: The fCal and fNeo concentrations differed significantly in clinically and endoscopically active IBD when compared with those in patients with inactive disease. Both fCal and fNeo concentrations correlated closer with endoscopic scores in UC (r = 0.75 and r = 0.72, respectively; P < 0.0001 for both) than in CD (r = 0.53 and r = 0.47, respectively; P < 0.0001 for both). Using cutoffs of 250 µg/g for fCal and 200 pmol/g for fNeo, both fecal markers had similar overall accuracies to predict endoscopic activity in patients with CD (74%) and also a higher and similar accuracies (88% and 90%, respectively) in patients with UC, whereas accuracies of C-reactive protein were slightly lower in patients with CD and UC. CONCLUSIONS: The fNeo is a novel reliable surrogate biomarker with the potential to identify patients with IBD with active mucosal lesions and represents an alternative marker as accurate as fCal to predict and monitor the severity of mucosal damages in patients with IBD.

S1PR5 is pivotal for the homeostasis of patrolling monocytes.

Patrolling Ly6C(-) monocytes are blood-circulating cells that play a role in inflammation and in the defense against pathogens. Here, we show that similar to natural killer (NK) cells, patrolling monocytes express high levels of S1PR5, a G-coupled receptor for sphingosine-1 phosphate. We found that S1pr5(-/-) mice lack peripheral Ly6C(-) monocytes but have a normal number of these cells in the bone marrow (BM). Various lines of evidence exclude a direct contribution of S1PR5 in the survival of Ly6C(-) monocytes at the periphery. Rather, our data support a role for S1PR5 in the egress of Ly6C(-) monocytes from the BM. In particular, we observed a reduced frequency of patrolling monocytes in BM sinusoids of S1PR5 KO mice. Unexpectedly, S1P was not a chemoattractant for patrolling monocytes and had no significant effect on their viability in vitro. Moreover, the disruption of S1P gradients in vivo did not alter Ly6C(-) monocyte trafficking and viability. These data suggest that S1PR5 regulates the trafficking of monocytes via a mechanism independent of S1P gradients.

Invariant NKT cells suppress CD8(+) T-cell-mediated allergic contact dermatitis independently of regulatory CD4(+) T cells.

Invariant natural killer T (iNKT) cells expressing a CD1d-restricted invariant αßTCR have key regulatory roles in autoimmunity, pathogen immunity, and tumor surveillance, but their function in the control of allergic skin diseases remains poorly documented. Using a model of contact hypersensitivity (CHS) to the hapten DNFB, we show here that iNKT cell deficiency results in enhanced skin inflammation due to augmented hapten-specific IFN-γ-producing CD8(+) effectors in skin draining lymph nodes (dLNs) and their massive recruitment into the allergen-exposed skin. Adoptive transfer and antibody depletion experiments as well as in vitro studies revealed that iNKT cells (1) reduce the severity of CHS, even in presensitized mice, (2) require hapten presentation by CD1d(+) dendritic cells (DCs) to dampen skin inflammation, and (3) produce IL-4 and IL-13 after CD1d-dependent in vitro stimulation by hapten-loaded DCs only in the presence of IFN-γ released from activated CD8(+) effector T cells. In corollary, mice double deficient in IL-4 and IL-13 exhibit an exacerbated CHS. Finally, iNKT-suppressive function is independent of Foxp3(+) regulatory T cells (Tregs). These data highlight that, besides Foxp3(+) Tregs, iNKT cells are potent downregulators of CD8(+) T cell-mediated CHS, and underscore that both cell types are important for the regulation of allergic skin inflammation.

Langerhans cells protect from allergic contact dermatitis in mice by tolerizing CD8(+) T cells and activating Foxp3(+) regulatory T cells.

Allergic contact dermatitis is the most frequent occupational disease in industrialized countries. It is caused by CD8(+) T cell-mediated contact hypersensitivity (CHS) reactions triggered at the site of contact by a variety of chemicals, also known as weak haptens, present in fragrances, dyes, metals, preservatives, and drugs. Despite the myriad of potentially allergenic substances that can penetrate the skin, sensitization is relatively rare and immune tolerance to the substance is often induced by as yet poorly understood mechanisms. Here we show, using the innocuous chemical 2,4-dinitrothiocyanobenzene (DNTB), that cutaneous immune tolerance in mice critically depends on epidermal Langerhans cells (LCs), which capture DNTB and migrate to lymph nodes for direct presentation to CD8(+) T cells. Depletion and adoptive transfer experiments revealed that LCs conferred protection from development of CHS by a mechanism involving both anergy and deletion of allergen-specific CD8(+) T cells and activation of a population of T cells identified as ICOS(+)CD4(+)Foxp3(+) Tregs. Our findings highlight the critical role of LCs in tolerance induction in mice to the prototype innocuous hapten DNTB and suggest that strategies targeting LCs might be valuable for prevention of cutaneous allergy.

CCR6/CCR10-mediated plasmacytoid dendritic cell recruitment to inflamed epithelia after instruction in lymphoid tissues.

Absent in peripheral tissues during homeostasis, human plasmacytoid dendritic cells (pDCs) are described in inflamed skin or mucosa. Here, we report that, unlike blood pDCs, a subset of tonsil pDCs express functional CCR6 and CCR10, and their respective ligands CCL20 and CCL27are detected in inflamed epithelia contacting blood dendritic cell antigen 2(+) pDCs. Moreover, pDCs are recruited to imiquimod-treated skin tumors in WT but not CCR6-deficient mice, and competitive adoptive transfers reveal that CCR6-deficient pDCs are impaired in homing to inflamed skin tumors after intravenous transfer. On IL-3 culture, CCR6 and CCR10 expression is induced on human blood pDCs that become responsive to CCL20 and CCL27/CCL28, respectively. Interestingly, unlike myeloid DC, blood pDCs initially up-regulate CCR7 expression and CCL19 responsiveness on IL-3 ± CpG-B and then acquire functional CCR6 and CCR10. Finally, IL-3-differentiated CCR6(+) CCR10(+) pDCs secrete high levels of IFN-α in response to virus. Overall, we propose an unexpected pDCs migratory model that may best apply for mucosal-associated lymphoid tissues. After CCR7-mediated extravasation into lymphoid tissues draining inflamed epithelia, blood pDCs may be instructed to up-regulate CCR6 and/or CCR10 allowing their homing into inflamed epithelia (in mucosae or skin). At this site, pDCs can then produce IFN-α contributing to pathogen clearance and/or local inflammation.

Regulatory T cells control type I food allergy to Beta-lactoglobulin in mice.

BACKGROUND: Regulatory T cells contribute to peripheral immune tolerance, yet their ability to control immediate-type hypersensitivity (ITH) reactions involved in IgE-mediated food allergy is still poorly documented. OBJECTIVES: We investigated in mice whether CD4+CD25+ regulatory T cells could control ITH to ß-lactoglobulin (BLG), a major allergen in cow's milk. METHODS: C3H/HeOuJ mice were sensitized by repeated oral gavage with BLG plus cholera toxin as adjuvant and orally challenged with BLG alone to elicit allergic symptoms. Mice were treated with the anti-CD25 mAb (PC61) before sensitization. Oral sensitization (afferent phase of ITH) was assessed by production of BLG-specific serum antibodies and Th1/Th2-type cytokines by specific CD4+ T cells in mesenteric lymph nodes. ITH was elicited by oral BLG challenge (efferent phase of ITH) and we monitored symptom scores, numbers and function of intestinal mast cells and serum level of the mucosal mast cell protease mMCP-1. RESULTS: Upon oral BLG challenge, orally sensitized mice developed only mild clinical signs. Anti-CD25 mAb-treated mice exhibited enhancement of both BLG-specific CD4+ T cell priming with IL-4, IL-5, IL-13 and IFN-γ production and total IgE, and BLG-specific IgE, IgG1 and IgG2a in serum. Anti-CD25 mAb treatment caused more severe symptoms upon BLG challenge, which correlated with enhanced serum levels of the mucosal mast cell protease mMCP-1. CONCLUSIONS: These data document that constitutive CD4+CD25+ regulatory T cells alleviate clinical signs of ITH to dietary BLG by modulating the priming of BLG-specific T and B cell responses during oral sensitization and enhancing mast cell degranulation.

Therapy with anti-TNFα antibody enhances number and function of Foxp3(+) regulatory T cells in inflammatory bowel diseases.

BACKGROUND: Inflammatory bowel diseases (IBDs) are associated with up-regulation of TNFα, hyperactivation of proinflammatory effector T cells (Teffs) and inefficient control by regulatory CD4(+) CD25(+) Foxp3(+) T cells (Tregs). The aim of this prospective study was to investigate the short-term impact of treatment of IBD patients with anti-TNFα antibodies (infliximab or adalimumab) on the frequency, phenotype, and suppressive function of Tregs. METHODS: Active IBD patients including 16 with Crohn's disease and 9 with ulcerative colitis were treated with anti-TNFα mAb. PBMCs were harvested immediately before and 2 weeks after the first injection. The frequency and phenotype of circulating CD4(+) CD25(+) Foxp3(+) Tregs were analyzed by flow cytometry, and their suppressive function was assessed by the ability of purified CD4(+) CD25(+) CD127(-) Tregs to inhibit the proliferation of allogenic CD4(+) CD25(-) Teffs. RESULTS: CD4(+) CD25(+) Foxp3(+) Treg frequency was significantly lower in active IBD patients than in controls (2.8% ± 0.4% vs. 4.6% ± 0.6%, respectively; P = 0.01). On day 14 following the first anti-TNFα infusion, the frequency of circulating Tregs was significantly enhanced in IBD patients (4.0% ± 0.5% vs. 2.8% ± 0.4%, before treatment; P = 0.001), with a 2- to 3-fold increase in the intensity of Foxp3 expression. In addition, infliximab treatment enhanced the suppressive function of circulating Tregs, as shown by inhibition of Teff proliferation at a 1:8 Treg/Teff ratio (28% ± 5% vs. 66% ± 10%, after treatment; P = 0.04). CONCLUSIONS: These data demonstrate that anti-TNFα treatment of active IBD rapidly enhances the frequency of functional Foxp3(+) Tregs in blood and potentiates their suppressive function. This indicates that Treg potentiation may represent an unanticipated outcome of anti-TNFα biotherapy in IBD.