T follicular helper cells are the main CD4(+) T cells specialized in supporting B-cell responses, but their role in driving transfusion-associated alloimmunization is not fully characterized. Reports ...of T follicular helper subsets displaying various markers and functional activities underscore the need for better characterization/identification of markers with defined functions. Here we show that a previously unidentified subset of human circulating T follicular helper cells expressing TIGIT, the T-cell immunoreceptor with Ig and immunoreceptor tyrosine-based inhibitory domains, exhibit strong B-cell help functions. Compared to the subset lacking the receptor, T follicular helper cells expressing this receptor up-regulated co-stimulatory molecules and produced higher levels of interleukins (IL-21 and IL-4) critical for promoting B-cell activation/differentiation. Furthermore, this subset was more efficient at inducing the differentiation of B cells into plasmablasts and promoting immunoglobulin G production. Blocking antibodies abrogated the B-cell help properties of receptor-expressing T follicular helper cells, consistent with the key role of this molecule in T follicular helper-associated responses. Importantly, in chronically transfused patients with sickle cell anemia, we identified functional differences of this subset between alloimmunized and non-alloimmunized patients. Altogether, these studies suggest that expression of the T-cell immunoreceptor with Ig and immunoreceptor tyro-sine-based inhibitory domains not only represents a novel circulating T follicular helper biomarker, but is also functional and promotes strong B-cell help and ensuing immunoglobulin G production. These findings open the way to defining new diagnostic and therapeutic strategies in modulating humoral responses in alloimmunization, and possibly vaccination, autoimmunity and immune deficiencies.
The human colonic mucosa contains regulatory type 1-like (Tr1-like, i.e., IL-10-secreting and Foxp3-negative) T cells specific for the gut
, which are both decreased in Crohn's disease patients. ...These data, together with the demonstration, in mice, that colonic regulatory T cells (Treg) induced by
bacteria are key players in colon homeostasis, support a similar role for
-specific Treg in the human colon. Here we assessed the mechanisms whereby
induces human colonic Treg. We demonstrated that
, but not related Clostridia, skewed human dendritic cells to prime IL-10-secreting T cells. Accordingly,
induced dendritic cells to express a unique array of potent Tr1/Treg polarizing molecules: IL-10, IL-27, CD39, IDO-1, and PDL-1 and, following TLR4 stimulation, inhibited their up-regulation of costimulation molecules as well as their production of pro-inflammatory cytokines IL-12 (p35 and p40) and TNFα. We further showed that these potent tolerogenic effects relied on
-induced TLR2/6 triggering, JNK signaling and CD39 ectonucleotidase activity, which was induced by IDO-1 and IL-27. These data, together with the presence of
-specific Tr1-like Treg in the human colon, point out to dendritic cells polarization by
as the first described cellular mechanism whereby the microbiota composition may affect human colon homeostasis. Identification of
-induced mediators involved in Tr1-like Treg induction by dendritic cells opens therapeutic avenues for the treatment of inflammatory bowel diseases.
In mice, microbiota-induced Tregs both maintain intestinal homeostasis and provide resistance to immuno-pathologies in the adult. Identifying their human functional counterpart therefore represents ...an important goal. We discovered, in the human colonic lamina propria and blood, a FoxP3-negative IL-10-secreting Treg subset, which co-expresses CD4 and CD8α (hence named DP8α) and displays a TCR-reactivity against
, indicating a role for this symbiotic bacterium in their induction. Moreover, supporting their role in intestinal homeostasis, we previously reported both their drastic decrease in IBD patients and their protective role
against intestinal inflammation, in mice. Here, we aimed at identifying the genomic, phenotypic and functional signatures of these microbiota-induced Tregs, towards delineating their physiological role(s) and clinical potential. Human
-reactive DP8α Treg clones were derived from both the colonic lamina propria and blood. RNA-sequencing, flow cytometry and functional assays were performed to characterize their response upon activation and compare them to donor- and tissue-matched FoxP3
Treg clones. DP8α Tregs exhibited a unique mixed Tr1-like/cytotoxic CD4
T cell-profile and shared the RORγt and MAF master genes with mouse gut microbiota-induced FoxP3
Tregs. We revealed their potent cytotoxic, chemotactic and IgA-promoting abilities, which were confirmed using
assays. Therefore, besides their induction by a
bacterium, DP8α Tregs also partake master genes with mouse microbiota-induced Tregs. The present identification of their complete signature and novel functional properties, should be key in delineating the
roles and therapeutic applications of these unique human microbiota-induced Tregs through their study in pathological contexts, particularly in inflammatory bowel diseases.
Transfusions are the main treatment for patients with sickle cell disease. However, alloimmunization remains a major life-threatening complication for these patients, but the mechanism underlying ...pathogenesis of alloimmunization is not known. Given the chronic hemolytic state characteristic of sickle cell disease, resulting in release of free heme and activation of inflammatory cascades, we tested the hypothesis that anti-inflammatory response to heme is compromised in alloimmunized sickle patients, increasing their risk of alloimmunization. Heme-exposed monocyte-derived dendritic cells from both non-alloimmunized sickle patients and healthy donors inhibited priming of pro-inflammatory CD4(+) type 1 T cells, and exhibited significantly reduced levels of the maturation marker CD83. In contrast, in alloimmunized patients, heme did not reverse priming of pro-inflammatory CD4(+) cells by monocyte-derived dendritic cells or their maturation. Furthermore, heme dampened NF-κB activation in non-alloimmunized, but not in alloimmunized monocyte-derived dendritic cells. Heme-mediated CD83 inhibition depended on Toll-like receptor 4 but not heme oxygenase 1. These data suggest that extracellular heme limits CD83 expression on dendritic cells in non-alloimmunized sickle patients through a Toll-like receptor 4-mediated pathway, involving NF-κB, resulting in dampening of pro-inflammatory responses, but that in alloimmunized patients this pathway is defective. This opens up the possibility of developing new therapeutic strategies to prevent sickle cell alloimmunization.
The FUT2 α1,2fucosyltransferase contributes to the synthesis of fucosylated glycans used as attachment factors by several pathogens, including noroviruses and rotaviruses, that can induce ...life-threatening gastroenteritis in young children.
genetic polymorphisms impairing fucosylation are strongly associated with resistance to dominant strains of both noroviruses and rotaviruses. Interestingly, the wild-type allele associated with viral gastroenteritis susceptibility inversely appears to be protective against several inflammatory or autoimmune diseases for yet unclear reasons, although a
influence on microbiota composition has been observed. Here, we studied a cohort of young healthy adults and showed that the wild-type
allele was associated with the presence of anti-RVA antibodies, either neutralizing antibodies or serum IgA, confirming its association with the risk of RVA gastroenteritis. Strikingly, it was also associated with the frequency of gut microbiota-induced regulatory T cells (Tregs), so-called DP8α Tregs, albeit only in individuals who had anti-RVA neutralizing antibodies or high titers of anti-RVA IgAs. DP8α Tregs specifically recognize the human symbiont
, which strongly supports their induction by this anti-inflammatory bacterium. The proportion of
in feces was also associated with the
wild-type allele. These observations link the
genotype with the risk of RVA gastroenteritis, the microbiota and microbiota-induced DP8α Treg cells, suggesting that the anti-RVA immune response might involve an induction/expansion of these T lymphocytes later providing a balanced immunological state that confers protection against inflammatory diseases.
Abundance of
Faecalibacterium prausnitzii
, a dominant bacterium of the human microbiota that exhibits antiinflammatory effects, is decreased in patients with inflammatory bowel diseases (IBD). In ...humans, colonic lamina propria contains IL-10–secreting, Foxp3
–
Tregs characterized by a double expression of CD4 and CD8α (DP8α) and a specificity for
F. prausnitzii
. This Treg subset is decreased in IBD. The in vivo effect of DP8α cells has not been evaluated yet to our knowledge. Here, using a humanized model of a NSG immunodeficient mouse strain that expresses the HLA D–related allele HLA-DR*0401 but not murine class II (NSG-Ab° DR4) molecules, we demonstrated a protective effect of a HLA-DR*0401–restricted DP8α Treg clone combined with
F. prausnitzii
administration in a colitis model. In a cohort of patients with IBD, we showed an independent association between the frequency of circulating DP8α cells and disease activity. Finally, we pointed out a positive correlation between
F. prausnitzii
–specific DP8α Tregs and the amount of
F. prausnitzii
in fecal microbiota in healthy individuals and patients with ileal Crohn’s disease.
Toll-like receptor (TLR) agonists are promising adjuvants for immune therapy of cancer, but their potential efficacy as single or combinatorial agents has yet to be fully evaluated. Here, we report ...that among all TLR agonists tested, dendritic cells (DC) stimulated with the TLR3 agonist polyI:C displayed the strongest activity in stimulating proinflammatory responses and the production of melanoma antigen-specific CD8(+) T cells. Simultaneous treatment with TLR7/8 agonists further improved these responses, but the inclusion of bacterial lipopolysaccharide (LPS), a TLR4 agonist, suppressed proinflammatory cytokine production. This inhibition was contingent upon rapid induction of the suppressive cytokine interleukin (IL)-10 by LPS, leading to dysregulated immune responses and it could be reversed by signal transducers and activators of transcription 3 knockdown, p38 blockade or antibodies to IL-10 and its receptor. Our findings show how certain TLR agonist combinations can enhance or limit DC responses associated with antitumor immunity, through their relative ability to induce IL-10 pathways that are immune suppressive.
Matrix metalloproteinase-2 (MMP-2) is involved in several physiological mechanisms, including wound healing and tumor progression. We show that MMP-2 directly stimulates dendritic cells (DCs) to both ...upregulate OX40L on the cell surface and secrete inflammatory cytokines. The mechanism underlying DC activation includes physical association with Toll-like receptor-2 (TLR2), leading to NF-κB activation, OX40L upregulation on DCs, and ensuing TH2 differentiation. Significantly, MMP-2 polarizes T cells toward type 2 responses in vivo, in a TLR2-dependent manner. MMP-2-dependent type 2 polarization may represent a key immune regulatory mechanism for protection against a broad array of disorders, such as inflammatory, infectious, and autoimmune diseases, which can be hijacked by tumors to evade immunity.
HLA-E are nonclassical MHC molecules with poorly characterized tissue distribution and functions. Because of their capacity to bind the inhibitory receptor, CD94/NKG2A, expressed by NK cells and CTL, ...HLA-E molecules might play an important role in immunomodulation. In particular, expression of HLA-E might favor tumor cell escape from CTL and NK immunosurveillance. To address the potential role of HLA-E in melanoma immunobiology, we assessed the expression of these molecules ex vivo in human melanoma biopsies and in melanoma and melanocyte cell lines. Melanoma cell lines expressed no or low surface, but significant intracellular levels of HLA-E. We also report for the first time that some of them produced a soluble form of this molecule. IFN-gamma significantly increased the surface expression of HLA-E and the shedding of soluble HLA-E by these cells, in a metalloproteinase-dependent fashion. In contrast, melanocyte cell lines constitutively expressed HLA-E molecules that were detectable both at the cell surface and in the soluble form, at levels that were poorly affected by IFN-gamma treatment. On tumor sections, a majority of tumor cells of primary, but a low proportion of metastatic melanomas (30-70 and 10-20%, respectively), expressed HLA-E. Finally, HLA-E expression at the cell surface of melanoma cells decreased their susceptibility to CTL lysis. These data demonstrate that HLA-E expression and shedding are normal features of melanocytes, which are conserved in melanoma cells of primary tumors, but become dependent on IFN-gamma induction after metastasis. The biological significance of these findings warrants further investigation.
The matrix metalloproteinase-2 (MMP-2), overexpressed in most cancers, induces TH2 polarization by conditioning dendritic cells to over-express OX40L and downregulate IL-12p70 through the degradation ...of the type-I IFN receptor IFNAR1. Elucidating mechanisms underlying detrimental tumor-associated type-2 responses represent a crucial step in designing effective immune therapies to treat cancer patients.
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