Antigen concentration determines helper T cell subset participation in IgE antibody responses

Effects of increasing sensitizing doses of ovalbumin on airway hyperresponsiveness in asthmatic mice

BACKGROUND

The dosage of ovalbumin (OVA) during the sensitization stage is considered a crucial factor in the development of airway hyperresponsiveness (AHR). However, the inconsistent dosages of sensitizing OVA used in current studies and the lack of research on their impact on AHR are notable limitations.

METHODS

We examined the impact of increasing sensitizing doses of OVA in a murine asthma model, which entailed initial sensitization with OVA followed by repeated exposure to OVA aerosols. BALB/c mice were primed with doses of OVA (0, 10, 20, 50, and 100 μg) plus 1 mg Alum on Days 0 and 7, and were challenged with OVA aerosols (10 mg/mL for 30 min) between Days 14 and 17. Antigen-induced AHR to methacholine (MCh), as well as histological changes, eosinophilic infiltration, and epithelial injury were assessed.

RESULTS

The result indicated that there are striking OVA dose-related differences in antigen-induced AHR to MCh. The most intense antigen-induced AHR to MCh was observed with sensitization at 50 μg, while weaker responses were seen at 10, 20, and 100 μg. Meanwhile, there was a significant increase in eosinophil count with sensitization at 50 μg. The changes of AHR were correlated with total cells count, lymphocytes count, eosinophils count, and basophils count in bronchoalveolar lavage fluid; however, it did not correlate with histological changes such as cellular infiltration into bronchovascular bundles and goblet cell hyperplasia of the bronchial epithelium.

CONCLUSION

Overall, this study demonstrated that sensitization with 50 μg of OVA resulted in the most significant AHR compared to other dosages. These findings may offer valuable insights for future research on mouse asthma modeling protocols.

A mechanism for hunchback promoters to readout morphogenetic positional information in less than a minute

Cell fate decisions in the fly embryo are rapid: hunchback genes decide in minutes whether nuclei follow the anterior/posterior developmental blueprint by reading out positional information in the Bicoid morphogen. This developmental system is a prototype of regulatory decision processes that combine speed and accuracy. Traditional arguments based on fixed-time sampling of Bicoid concentration indicate that an accurate readout is impossible within the experimental times. This raises the general issue of how speed-accuracy tradeoffs are achieved. Here, we compare fixed-time to on-the-fly decisions, based on comparing the likelihoods of anterior/posterior locations. We found that these more efficient schemes complete reliable cell fate decisions within the short embryological timescales. We discuss the influence of promoter architectures on decision times and error rates, present concrete examples that rapidly readout the morphogen, and predictions for new experiments. Lastly, we suggest a simple mechanism for RNA production and degradation that approximates the log-likelihood function.

An Experimental Model of Eosinophilic Chronic Rhinosinusitis Induced by Bacterial Toxins in Rabbits

Background

The pathophysiology of chronic rhinosinusitis (CRS) is still not well known due to the multifactorial etiologies involved. Bacteria play a role in the pathogenesis of CRS by various means, including biofilm adhesion, intracellular persistence, or inducing inflammation secondary to toxins. Endotoxins and exotoxins, especially Staphylococcus aureus superantigens, can produce significant immune responses in the host and are implicated in patients with CRS. The majority of animal models described for CRS revalidates the pathophysiology of acute sinusitis, ostium occlusion, or foreign body associated infection.

Objectives

To evaluate an experimental model of eosinophilic CRS using prolonged exposure to bacterial toxins. The histological changes in rabbits exposed to S. aureus enterotoxin B (SEB), lipopolysaccharide (LPS), or lipoteichoic acid (LTA) were compared.

Methods

After induction with ovalbumin (OVA) sensitization with subcutaneous injection for 2 weeks, rabbits underwent surgery to insert an indwelling catheter into the maxillary sinus. The sinus was irrigated with OVA 3 times weekly for 2 weeks, followed by sinus irrigation with bacterial toxin (SEB: 1 µg/mL, LPS: 100 ng/mL, or LTA: 100 ng/mL) 3 times weekly for 4 weeks. The histological changes in the treated sinus were compared with control rabbits.

Results

Sinuses exposed to bacterial toxins (SEB, LPS, and LTA) produced significant mucosal thickening with infiltration of inflammatory cells, notably eosinophils. SEB was the only toxin that promoted a mixed pattern of inflammation, including eosinophilic and neutrophilic infiltration.

Conclusion

Our experimental model of eosinophilic CRS in rabbits produced significant mucosal thickening and inflammation in the sinuses exposed to bacterial toxins, with histological changes analogous to what is observed in patients with CRS with nasal polyps. This model may serve as a basis for future investigation of the pathogenesis of eosinophilic CRS in relation to bacterial toxins or as a model for testing new therapeutic modalities for this disease.

Staphylococcus aureus enterotoxin B contributes to induction of nasal polypoid lesions in an allergic rhinosinusitis murine model

BACKGROUND

Studies on the pathophysiology of nasal polyps in human subjects have been limited; thus an animal model is needed. There is increasing evidence supporting the role of Staphylococcus aureus enterotoxin B (SEB) in the pathogenesis of nasal polyposis. The aim of this study was to investigate the histological and immunologic effects of SEB on the formation of nasal polypoid lesions in an allergic rhinosinusitis murine model.

METHODS

After induction of an ovalbumin (OVA)-induced allergic rhinosinusitis, OVA with SEB (5 or 500 ng) was instilled into the nasal cavity of mice for 8 weeks. Control mice did not receive SEB or OVA instillation. Histopathological changes were observed using hematoxylin and eosin, Sirius red, Giemsa, Masson's trichrome, and Alcian blue stains. The levels of interleukin (IL)-4, IL-5, IL-8, IL-13, eotaxin, interferon gamma, total IgE, and OVA-specific IgE from serum or nasal lavage fluid were measured using enzyme-linked immunosorbent assay.

RESULTS

The group treated with OVA plus 5 ng of SEB had significantly more mucosal lesions with epithelial disruption and nasal polypoid lesions than mice treated with OVA only, showing a significant increase in the infiltration of total inflammatory cells, eosinophils, and lymphocytes than the other groups. Levels of IL-5, eotaxin, and OVA-specific IgE in nasal lavage fluid were increased in the group treated with OVA plus 5 ng of SEB than in the other groups. A higher number of secretory cells in the groups treated with OVA plus SEB was observed than in other groups.

CONCLUSION

Low-dose SEB induced nasal polypoid lesions with an increased eosinophilic infiltration in an allergic rhinosinusitis murine model.

Immunological and metabolomic impacts of administration of Cry1Ab protein and MON 810 maize in mouse

We have investigated the immunological and metabolomic impacts of Cry1Ab administration to mice, either as a purified protein or as the Cry1Ab-expressing genetically modified (GM) MON810 maize. Humoral and cellular specific immune responses induced in BALB/cJ mice after intra-gastric (i.g.) or intra-peritoneal (i.p.) administration of purified Cry1Ab were analyzed and compared with those induced by proteins of various immunogenic and allergic potencies. Possible unintended effects of the genetic modification on the pattern of expression of maize natural allergens were studied using IgE-immunoblot and sera from maize-allergic patients. Mice were experimentally sensitized (i.g. or i.p. route) with protein extracts from GM or non-GM maize, and then anti-maize proteins and anti-Cry1Ab–induced immune responses were analyzed. In parallel, longitudinal metabolomic studies were performed on the urine of mice treated via the i.g. route. Weak immune responses were observed after i.g. administration of the different proteins. Using the i.p. route, a clear Th2 response was observed with the known allergenic proteins, whereas a mixed Th1/Th2 immune response was observed with immunogenic protein not known to be allergenic and with Cry1Ab. This then reflects protein immunogenicity in the BALB/c Th2-biased mouse strain rather than allergenicity. No difference in natural maize allergen profiles was evidenced between MON810 and its non-GM comparator. Immune responses against maize proteins were quantitatively equivalent in mice treated with MON810 vs the non-GM counterpart and no anti-Cry1Ab–specific immune response was detected in mice that received MON810. Metabolomic studies showed a slight “cultivar” effect, which represented less than 1% of the initial metabolic information. Our results confirm the immunogenicity of purified Cry1Ab without evidence of allergenic potential. Immunological and metabolomic studies revealed slight differences in mouse metabolic profiles after i.g. administration of MON810 vs its non-GM counterpart, but no significant unintended effect of the genetic modification on immune responses was seen.

Are we getting enough allergens?

This paper proposes that reduced allergen exposure is one of the factors underlying the higher risk of IgE-mediated allergic disease in populations with an urbanized, westernized, and affluent lifestyle. This lower allergen exposure results in the failure to induce and maintain immune tolerance to common environmental allergens. The paper summarizes different lines of evidence that may support or contradict this hypothesis and points to areas where more knowledge is needed.

Intranasal exposure to bacterial superantigens induces airway inflammation in HLA class II transgenic mice

Staphylococcus aureus is widely prevalent in the nasopharynges of healthy individuals (carriers) but can also cause serious infections. S. aureus can elaborate a variety of superantigen exotoxins in "carrier" or "pathogenic" states. Streptococcus pyogenes can also colonize the nasopharynx and elaborate superantigens. Unlike the acute effects of superantigen exotoxins absorbed through the gut or vaginal mucosa, little is known regarding the pathogenesis of superantigens entering through the intranasal route. In the current study, we evaluated the local and systemic effects of staphylococcal enterotoxin B (SEB) and streptococcal pyrogenic exotoxin A (SPEA) delivered through the intranasal route. Superantigens were administered intranasally on multiple occasions, and experimental animals were sacrificed on day 8 for experimental analyses. SEB-induced airway inflammation was more pronounced for HLA-DR3 transgenic mice than for BALB/c mice, consistent with bacterial superantigens binding more efficiently to human than murine major histocompatibility complex class II. The nature of the airway inflammation in HLA-DR3 mice was determined by the concentration of SEB applied intranasally. Low concentrations (20 ng) induced eosinophilic airway inflammation as well as eosinophil degranulation, whereas intranasal exposure to higher concentrations (2,000 ng) resulted in neutrophilic airway inflammation, permanent airway destruction, toxic shock, and mortality. SEB-induced eosinophilic inflammatory response was enhanced in signal transducer and activator of transcription (STAT)-4-deficient HLA-DQ8 transgenic mice with defective interleukin-12 signaling. Intranasal administration of SPEA induced airway inflammation and systemic immune activation in HLA-DQ8 transgenic mice. In conclusion, repeated chronic intranasal exposure to bacterial superantigens causes airway inflammation and systemic immune activation.

Induction of allergic inflammation in the lungs of sensitized sheep after local challenge with house dust mite

BACKGROUND

Previous sheep models of asthma are based on sheep sensitized to nematode (Ascaris) allergens and these have been used to evaluate the physiological and pharmacological effects of potential anti-asthma agents. The immunological mechanisms associated with the allergic response in sheep lungs has not been examined in detail.

OBJECTIVE

To develop an experimental sheep model of allergic lung inflammation based on a relevant major human allergen, house dust mite, and to define the immunological features of the allergic response in this model.

METHODS

Sheep immunized subcutaneously with solubilized house dust mite extract were given a single bronchial challenge with house dust mite. Bronchoalveolar lavage (BAL) and peripheral blood leucocytes were collected before and after challenge for flow cytometry, and tissue samples were taken post-mortem (48 h post-challenge) for histology and immunohistochemical analyses.

RESULTS

Immunizations with 50 microg house dust mite induced an allergen-specific IgE response in 50 to 60% of sheep (allergic sheep), with higher antigen doses increasing specific IgG1 but not IgE. Lung challenge of allergic sheep with house dust mite led to the initial recruitment of neutrophils (at 6 h post-challenge) followed by eosinophils and activated lymphocytes into the lung tissue and BAL, similar to the late-phase allergic response seen in human asthma. Eosinophil recruitment peaked at 48 h post-challenge, representing 10 to 33% of BAL leucocytes in allergen-challenged allergic sheep compared to 0 to 3% in allergen-challenged control (naïve) sheep. Lymphocytes recovered from the lung after allergen challenge were enriched for CD4+ T cells and were more activated than lymphocytes in blood. There was significant down-regulation of CD62L (L-selectin) and CD49d (VLA-4) expression after allergen challenge on BAL eosinophils and lymphocytes compared to blood. In addition, VCAM-1 (ligand for VLA-4) was up-regulated on blood vessels of allergen-challenged lungs. Eosinophils, CD4+ T cells and CD45R+ B cells were the most prominent leucocytes found in lung tissue 48 h after allergen challenge.

CONCLUSION

This study demonstrates, for the first time, the ability of house dust mite to induce allergic responses in sheep lungs. This novel sheep model of allergic lung inflammation using relevant human allergens, exhibits similarities to human asthmatic disease and will be a useful tool for studies of the immunological and physiological mechanisms of allergic asthma.

Effect of different sensitizing doses of antigen in a murine model of atopic asthma

The dose of antigen is assumed to be one of the important factors in the polarized development of helper T cell subsets, i.e. Th1 or Th2 cells. We investigated the effect of the sensitizing antigen dose in a murine model of atopic asthma, which involved sensitization with ovalbumin (OVA) followed by repeated exposure to OVA aerosols. BALB/c mice were primed with varying doses of OVA (0, 10, 100 and 1000 microg) plus Al(OH)3 on days 0, 7 and 14, and were challenged with OVA aerosols (50 mg/ml for 20 min) on days 15-20. There were striking antigen dose-related differences in OVA-specific antibodies: high IgE and low IgG2a titres were found in mice sensitized at 10 microg, while low IgE and high IgG2a titres were seen at 1000 microg. The sensitizing dose was inversely correlated with the total cell count and the eosinophil count in bronchoalveolar lavage fluid (BALF), as well as with the extent of histological changes such as goblet cell hyperplasia of the bronchial epithelium and cellular infiltration into bronchovascular bundles. Antigen-induced bronchial hyper-responsiveness (BHR) to methacholine was observed with sensitization at 10 microg but not at 1000 microg. Splenic mononuclear cells (SMNC) obtained from mice sensitized at either dose showed proliferation in response to OVA. Production of IL-4 and IL-5 by OVA-stimulated SMNC was inversely correlated with the dose of sensitizing antigen. High-dose sensitization resulted in general suppression of cytokine production by SMNC, including interferon-gamma (IFN-gamma). The BALF levels of IL-4 and IL-5 were increased by low-dose sensitization, whereas IFN-gamma and IL-12 levels were increased by high-dose sensitization. These results suggest that the dose of sensitizing antigen defines the phenotypic changes in the present murine asthma model, presumably by influencing the pattern of cytokine production.

Antigen dose-dependent differences in IgE antibody production are not due to polarization towards Th1 and Th2 cell subsets

The quality of the humoral immune response against protein antigens in CBA/J mice is dependent on the antigen dose used for immunization: low doses induce high titers of IgE antibodies, whereas high doses promote the production of IgG2a antibodies but inhibit IgE formation. To investigate whether the reciprocal regulation of antibody production is possibly due to a differential activation of Th1 and Th2 cell populations in the two immunization groups, the cytokine pattern of spleen cells from both groups, cultured with antigen in vitro, was analyzed by measurement of intracellular and secreted cytokine levels. The data presented show that in vitro restimulated spleen cells from mice primed with low as well as with high doses of antigen produce predominantly the Th2 cytokines IL-4 and IL-10 but reduced levels of IL-12. The release of IFN-gamma is only slightly enhanced compared to unstimulated control cultures. The results indicate that CD4+ T cells in both groups belong mainly to the Th2 cell subset. This finding is contradictory to the general allegation that the antigen dose is decisive for the polarization of Th1 versus Th2 immune responses and shows that the antigen dose-dependent regulation of IgE antibody production is not due to differential polarization towards Th1 and Th2 cells.

Antigen dose-dependent predominance of either direct or sequential switch in IgE antibody responses

Priming of CBA/J mice with minute doses of protein antigens (Ag) leads to high IgE antibody (Ab) titres in the immune sera of these animals. In contrast priming with large doses elicits only a marginal production of IgE Ab. In vitro restimulation of spleen cells from animals primed with large doses and lacking in vivo IgE Ab leads to a burst of IgE Ab-forming cells. This in vitro anamnestic response is lacking in mice primed with minute doses of Ag. In order to trace the cellular basis of the in vitro IgE memory response we have extended the analysis of the distribution of Ab isotypes to Ag-primed IgG1-deficient delta 5'S gamma 1 mice. The data presented here must be interpreted as followed. Priming of mice with minute doses of Ag leads to a direct switch from IgM to IgE Ab expression in both strains. These animals have high IgE Ab titres without establishing an IgE memory. The direct switch was verified by polymerase chain reaction and Southern blot analysis of switch circle DNA isolated from Ag-specific B cells of CBA/J mice primed with minute doses of Ag. In contrast to immunization with minute doses, priming with large doses of Ag fails to induce in vivo IgE Ab production in CBA/J and delta 5'S gamma 1 mice but establishes a B epsilon memory in CBA/J mice which involves IgG1-bearing intermediate B cells. In vivo these B epsilon memory cells do not enter the status of IgE Ab-producing cells. In vitro they can be released from this anergy and presumed suppression and develop in an anamnestic response into a large population of IgE Ab-forming B cells. This increase in the number of IgE Ab-producing cells after restimulation in vitro is lacking in delta 5'S gamma 1 mice, apparently because of their inability to generate IgG1-expressing precursor cells. The notion of a sequential switch and an IgG1 intermediate B epsilon memory status is also supported by depletion and inhibition experiments. Elimination of IgG1-expressing B cells in CBA/J mice primed with high doses of Ag prevents the IgE Ab burst after in vitro challenge with Ag. The data further suggest that the two switch pathways are not mutually exclusive and that the Ag dose can decide which pathway is preferentially used.

Induction of Th1 and Th2 CD4+ T cell responses: the alternative approaches

T helper lymphocytes can be divided into two distinct subsets of effector cells based on their functional capabilities and the profile of cytokines they produce. The Th1 subset of CD4+ T cells secretes cytokines usually associated with inflammation, such as IFN-gamma and TNF and induces cell-mediated immune responses. The Th2 subset produces cytokines such as IL-4 and IL-5 that help B cells to proliferate and differentiate and is associated with humoral-type immune responses. The selective differentiation of either subset is established during priming and can be significantly influenced by a variety of factors. One of these factors, the cytokine environment, has been put forward as the major variable influencing Th development and is already well reviewed by others. Instead, in the current review, we focus on some of the alternative approaches for skewing Th1/Th2 responses. Specifically, we discuss the effects on Th priming of (a) using altered peptide ligands as antigens, (b) varying the dose of antigen, and (c) altering costimulatory signals. The potential importance of each of these variables to influence immune responses to pathogens in vivo is discussed throughout.

In vitro investigation of factors influencing IgE synthesis

Cytokines play an important role in the induction or inhibition of synthesis of the particular isotypes of immunoglobulin after antigenic stimulation. Studies of these effects in vivo require substantial amounts of reagents that are difficult and time-consuming to prepare. The present paper describes methods for immunization and in vitro culture that permit the investigation of effects of cytokines and anti-cytokines on a secondary, antigen-specific IgE response, using much lower quantities of materials than are required in vivo. The results are compared with those reported from in vivo studies.

Interleukin 4 production by CD4+ T cells from allergic individuals is modulated by antigen concentration and antigen-presenting cell type

We have previously shown that CD4+ T cells from allergic individuals are predisposed to produce interleukin (IL)-4 in response to allergens, and that allergen immunotherapy greatly reduced IL-4 production in an allergen-specific fashion. The mechanism that results in the reduction of IL-4 synthesis in treated individuals is unknown, but because clinical improvement during immunotherapy is associated with the administration of the highest doses of allergen, we hypothesized that high concentration of allergen results in the downregulation of IL-4 synthesis in CD4+ T cells. In this report, we demonstrated that CD4+ T cells from allergic donors produced high levels of IL-4 when stimulated with low concentrations of allergen (0.003-0.01 micrograms/ml), particularly when B cell-enriched populations presented the antigen. In contrast, the same responding CD4+ T cell population produced little IL-4 when stimulated with high concentrations of allergen (10-30 micrograms/ml), especially when monocytes were used as antigen-presenting cells (APC). The quantity of IL-4 produced was also found to be inversely related to the extent of proliferation of the CD4+ T cells in response to allergen/antigen; maximal proliferation of CD4+ T cells occurred in response to high concentrations of antigen when IL-4 production was minimal. Antigen presentation by B cell-enriched populations, instead of monocytes, induced less CD4+ T cell proliferation, but induced much greater IL-4 synthesis. Moreover, the addition of increasing numbers of APC (either B cells or monocytes) to cultures containing a constant number of responder T cells resulted in increased T cell proliferation and decreased IL-4 production. These results indicate that the circumstances under which memory T cells are activated, as well as the strength of the proliferative signal to T cells, greatly affect the quantity of IL-4 produced. Thus, our observations that the cytokine profile of allergen-specific memory CD4+ T cells can indeed be modulated by the antigen dose and APC type suggest that methods that preferentially enhance allergen uptake by monocytes and that enhance T cell proliferation will improve the clinical efficacy of immunotherapy in the treatment of allergic disease.

Regulation of the interaction between Th1 and Th2 T cell clones to provide help for antibody production in vivo

On the premise that an individual with an intact immune system has the capability to develop both cellular and antibody immune responses supported by the balance between the lymphokines secreted by T helper (Th) cells, we studied the interaction between different types of Th cell clones in vivo and the parameters that may affect this interaction. We used an adoptive transfer system in which nude or lethally irradiated mice were reconstituted with histocompatible CD4+ keyhole limpet hemocyanin (KLH)-specific T cell clones with defined lymphokine profiles. This approach allowed us to study the effects of the cognate interaction between T and B cells in the presence of a defined set of lymphokines. We demonstrated that the co-transfer of both subsets of Th cells resulted in increased production of IgA, and decreased production of IgE and IgG2a. The concomitant presence of both cell types also increases their functional survival in vivo. We have shown that in the presence of a Th2 clone, higher immunization doses (above 100 micrograms trinitrophenol (TNP)-KLH/mouse) result in increased production of IgE and IgG1. In contrast, when a Th1 clone is present, low immunization doses (less than 50 micrograms TNP-KLH/mouse) resulted in increased production of IgG2a. We were also able to show that the neutralization of interleukin-4(IL-4) and or interferon-gamma (IFN-gamma) was sufficient to abrogate most of the regulatory effects caused by the Th2 or the Th1 clone respectively. Our results indicate that the subset of T cell(s) transferred determines the type of response obtained. In addition, the data presented indicate that the antigen dose used for immunization can modulate the quantitative parameters of the response. Furthermore, we have shown that the interaction between the two subsets of T cells in vivo is characterized by both antagonistic and agonistic effects and that most of the regulatory effects exerted by one subset over the other are mediated by IL-4 or IFN-gamma.