Co-administration of CD40 agonistic antibody and antigen fails to overcome the induction of oral tolerance

PLGA nanoparticles loaded with beta-lactoglobulin-derived peptides modulate mucosal immunity and may facilitate cow's milk allergy prevention

Beta-lactoglobulin (BLG)-derived peptides may facilitate oral tolerance to whey and prevent cow's milk allergy (CMA). Loading of BLG-peptides in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (Pep-NP) may improve this. Here we studied the uptake of NP and the capacity of NP and Pep-NP to activate bone marrow dendritic cells (BMDC). Furthermore, CMA prevention was evaluated by orally exposing three-week-old female C3H/HeOuJ mice to Pep-NP, NP or free peptides (PepMix) for 6 days before oral sensitization with whole whey protein and effects on the spleen and small intestine lamina propria (SI-LP) were studied. In BMDC, NP and Pep-NP enhanced CD40 expression and IL-6 and TNF-α secretion, while tended to decrease CD80 expression and prevented PepMix-induced IL-12 secretion. In vivo, oral exposure to Pep-NP, but not NP or PepMix, prior to whey sensitization tended to partially prevent the acute allergic skin response to whole whey protein. Splenocytes of NP-pre-exposed mice secreted increased levels of whey-specific IL-6, but this was silenced in Pep-NP-pre-exposed mice which also showed reduced TNF-α and IFN-γ secretion. In the SI-LP, Pep-NP pre-exposure reduced the CD4⁺ T cell frequency in CMA mice compared to PBS pre-exposure. In addition, while NP increased whey-specific IL-6 secretion in the SI-LP, Pep-NP did not and maintained regulatory TGF-β secretion. This study presents a proof-of-concept that PLGA nanoparticles facilitate the capacity of BLG peptides to suppress the allergic response to whole whey protein. Hence, PLGA nanoparticles may be further developed as an adjunct strategy for BLG-peptide-based oral tolerance induction and CMA prevention.

Functional maturation of lamina propria dendritic cells by activation of NKT cells mediates the abrogation of oral tolerance

We previously showed that although systemic administration of alpha-galactosylceramide (alphaGalCer) or agonistic anti-CD40 induced functional maturation of dendritic cells (DC) in mesenteric lymph nodes, only the former treatment succeeded in breaking the induction of oral tolerance. In this study, we looked for the essential factor responsible for the disruption of oral tolerance. We found that lamina propria (LP)-DC was responsible for the oral OVA presentation and that Peyer's patch was not essential for the induction of oral tolerance. Therefore, we investigated the role of LP-DC. Treatment with alphaGalCer but not with anti-CD40 induced the full maturation of LP-DC at an early time point. This functional activation of LP-DC was mediated by strong activation of NKT cells that reside abundantly in the small intestinal lamina propria (SI-LP) and interferon-gamma partially contributed to the LP-DC activation. LP-DC isolated from alphaGalCer-treated OVA-fed mice induced the differentiation of naïve CD4+ T cells into Th1 and Th2 and was associated with the reduced Foxp3+ population. In contrast, LP-DC isolated from anti-CD40-treated OVA-fed mice failed to generate Th cell differentiation but induced more Foxp3+ CD4+ T cells. Our results demonstrate that triggered by NKT cells in SI-LP, functional maturation of Ag-capturing DC from SI-LP is necessary for the abrogation of oral tolerance induction.

CD40/CD154 interactions are required for the optimal maturation of skin-derived APCs and the induction of helminth-specific IFN-gamma but not IL-4

The mechanisms through which Schistosoma mansoni larvae induce Th1 rather than Th2 immune responses are not well understood. In this study, using CD154-/- mice exposed to radiation-attenuated S. mansoni larvae, we demonstrate roles for CD154/CD40 in the activation of skin-derived APCs and the development of Th1 cells in the skin-draining lymph nodes (sdLN). The presence of CD154 was important for optimal IL-12p40 and essential for Ag-specific IFN-gamma, but CD154 expression by wild-type CD4- cells was insufficient to rescue recall responses of CD4+ cells from CD154-/- mice. This defect is probably due to impaired CD40-dependent IL-12 production in vivo, because administration of anti-CD40 Ab, or rIL-12, restored IFN-gamma production by sdLN cells from CD154-/- mice. CD154 ligation of CD40 was not required for the migration of skin-derived APCs, but did have a limited role in their maturation (increased MHC II and CD86). Unexpectedly, although CD4 cells from CD154-/- mice were deficient in their ability to produce IFN-gamma, they produced significant amounts of IL-4 and IL-5 in the presence of skin-derived APCs from wild-type and CD154-/- mice. Thus, in contrast to IFN-gamma, the production of Th2-associated cytokines is (in this model) independent of CD154. We conclude that whereas the priming of Th1 responses soon after exposure to schistosome larvae is completely CD40/CD154 dependent, IL-4, IL-5, and IL-13 are independent of CD154, suggesting a dichotomy in the specific mechanisms that induce these cytokines by CD4+ cells in the sdLN.

CD1d-restricted T cells license B cells to generate long-lasting cytotoxic antitumor immunity in vivo

Although resting B cells are known for being poorly immunogenic and for inducing T-cell tolerance, we have here attempted to test whether their immunogenicity could be enhanced by CD1d-restricted invariant T cells (iNKT) to a point where they could be used in cellular vaccines. We found that the addition of the iNKT ligand alpha-galactosylceramide (alphaGalCer) to peptide-loaded B cells overcame peptide-specific T-cell unresponsiveness and allowed for the generation of peptide-specific memory CTL immunity. This CTL was induced independently of CD4 T and natural killer cells but required iNKT and CD8 T cells. B cells directly primed CTL, and the alphaGalCer and the peptide must be presented on the same cell. Importantly, our B-cell-based vaccine is comparable in efficiency with dendritic cell-based vaccines, inducing similar CTL responses as well as providing an effective regimen for preventing and suppressing s.c. and metastatic tumors. Therefore, with the help of iNKT, peptide-pulsed B cells can establish long-lasting antitumor immunity and so show promise as the basis for an alternative cell-based vaccine.

Oral tolerance and allergic responses to food proteins

PURPOSE OF REVIEW

The default response to protein antigens in the intestine is the induction of systemic and local hyporesponsiveness, ensuring the prevention of coeliac disease and food allergies. Interest is increasing in the role of dietary manipulation and probiotics in treating allergic and other diseases, but less is known about how these regimens might influence systemic and local immune responses. This paper addresses the mechanisms at the interface of innate and adaptive immunity that determine how the body responds to orally administered proteins and how local bacteria modify these.

RECENT FINDINGS

This paper discusses evidence that dendritic cells in the intestinal mucosa are the critical cells that take up dietary proteins and migrate to the draining mesenteric lymph node, where they induce regulatory CD4 T-cell differentiation. The properties of tolerized T cells are discussed and it is proposed that the gut microenvironment maintains homeostasis by conditioning dendritic cells to remain in a quiescent state. Inhibitory signalling by commensal bacteria possibly contributes to this process.

SUMMARY

A regulatory network controls how dietary antigens are taken up and presented to T lymphocytes by specialized antigen-presenting cells. Elucidating their nature and how they are influenced by external factors such as probiotics may help develop novel therapies for allergy and help understand diseases such as coeliac disease.

Kinetics of costimulatory molecule expression by T cells and dendritic cells during the induction of tolerance versus immunity in vivo

Steady-state dendritic cells (DC) present peptide-MHC complexes to T cells in a tolerogenic manner, presumably because of deficient costimulation. However, it is clear that the path to tolerance involves initial T cell activation, suggesting that the deficit may lie in late-acting costimulatory molecules. With this in mind we have investigated the kinetics of expression of several costimulatory pairs on DC and OVA-reactive T cells after i.v. injection of mice with peptide and LPS (immunity), or peptide alone (tolerance). We find that T cells up-regulate CD154, OX40, RANKL and PD-1 whether they are destined for tolerance or immunity, although there are some differences in the levels and length of expression. In contrast, when analyzing DC, we found that up-regulation of CD80, CD86, CD40, RANK and PDL-1 occurred only when peptide was co-administered with LPS. These data give a picture of the T cell looking for costimulatory cues that are not forthcoming when pMHC is presented by steady-state DC, leading to tolerance. However, we did see a strong and rapid up-regulation of RANKL on T cells that occurred specifically when peptide was given in the absence of LPS, suggesting a possible positive signal influencing the decision between tolerance and immunity.

Preventing intolerance: the induction of nonresponsiveness to dietary and microbial antigens in the intestinal mucosa

The gut-associated lymphoid tissue (GALT) is constantly exposed to a variety of Ags and must therefore decipher a large number of distinct signals at all times. Responding correctly to each set of signals is crucial. When the GALT receives signals from the intestinal flora or food Ags, it must induce a state of nonresponsiveness (mucosal tolerance). In contrast, when pathogenic bacteria invade the intestinal mucosa, it is necessary to elicit strong T and B cell responses. The GALT is therefore in the position of constantly fighting intolerance to food and the commensal flora while effectively battling infectious microbes. Determining precisely which type of response to generate in each case is key to the prevention of immune dysregulation and tissue damage.

Split peripheral tolerance: CD40 ligation blocks tolerance induction for CD8 T?cells but not for CD4 T?cells in response to intestinal antigens

The role of antigen-presenting cells in the balance between immunity and tolerance to intestinal antigens remains poorly understood. In this study, we examined whether CD40 ligation affects the induction of CD4 and CD8 T cell tolerance in response to intestinal antigens. We show that an agonistic anti-CD40 mAb treatment did not block the induction of OVA-specific CD4 T cell tolerance, whereas this approach enabled strong priming of OVA-specific cytotoxic T cells (CTL), preventing CTL tolerance to intestinal antigen. Such CTL priming was independent of CD4 T cell help but required B7 costimulation. Co-administration of anti-CD40 mAb increased the synthesis of IL-2 and the expression of CD25 by CD8 T cells, but neither IL-2 production nor CD25 expression by CD4 T cells was enhanced by anti-CD40 mAb. However, neutralization of TGF-beta together with addition of agonistic anti-CD40 mAb was able to reverse CD4 T cell tolerance. These findings suggest that the induction of tolerance versus immunity against intestinal antigens is determined by the status of the antigen-presenting cells and that signals via CD40 differently regulate the outcome of CD4 and CD8 T cells in vivo.

CTLA-4 signaling regulates the intensity of hypersensitivity responses to food antigens, but is not decisive in the induction of sensitization

Although food allergy has emerged as a major health problem, the mechanisms that are decisive in the development of sensitization to dietary Ag remain largely unknown. CTLA-4 signaling negatively regulates immune activation, and may play a crucial role in preventing induction and/or progression of sensitization to food Ag. To elucidate the role of CTLA-4 signaling in responses to food allergens, a murine model of peanut allergy was used. During oral exposure to peanut protein extract (PPE) together with the mucosal adjuvant cholera toxin (CT), which induces peanut allergy, CTLA-4 ligation was prevented using a CTLA-4 mAb. Additionally, the effect of inhibition of the CTLA-4 pathway on oral exposure to PPE in the absence of CT, which leads to unresponsiveness to peanut Ag, was explored. During sensitization, anti-CTLA-4 treatment considerably enhanced IgE responses to PPE and the peanut allergens, Ara h 1, Ara h 3, and Ara h 6, resulting in elevated mast cell degranulation upon an oral challenge. Remarkably, antagonizing CTLA-4 during exposure to PPE in the absence of CT resulted in significant induction of Th2 cytokines and an elevation in total serum IgE levels, but failed to induce allergen-specific IgE responses and mast cell degranulation upon a PPE challenge. These results indicate that CTLA-4 signaling is not the crucial factor in preventing sensitization to food allergens, but plays a pivotal role in regulating the intensity of a food allergic sensitization response. Furthermore, these data indicate that a profoundly Th2-biased cytokine environment is insufficient to induce allergic responses against dietary Ag.